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Graft Polymerization: Starch as a Model Substrate
V. D. Athawale a; S. C. Rathi b
a
Department of Chemistry, University of Mumbai, Mumbai, India
b
Department of Chemistry, University of Mumbaim, Vidyanagari, Mumbai, India
Online Publication Date: 08 December 1999
To cite this Article: Athawale, V. D. and Rathi, S. C. (1999) 'Graft Polymerization:
Starch as a Model Substrate', Polymer Reviews, 39:3, 445 - 480
To link to this article: DOI: 10.1081/MC-100101424
URL: http://dx.doi.org/10.1081/MC-100101424
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J.M.S.—REV. MACROMOL. CHEM. PHYS., C39(3), 445–480 (1999)
Graft Polymerization:
Starch as a Model Substrate
V. D. ATHAWALE* and S. C. RATHI
Department of Chemistry
University of Mumbai, Vidyanagari
Mumbai 400 098, India
1. INTRODUCTION.................................................................................. 446
2. REVIEW PROFILE OF STARCH GRAFT COPOLYMERS .............
2.1. Grafting Parameters .....................................................................
2.2. Syntheses of Starch Graft Copolymers .......................................
2.3. Evidence for Grafting ..................................................................
2.4. Monomer Reactivity.....................................................................
2.5. Kinetics of Graft Polymerization.................................................
2.6. Copolymer Composition: Molecular Weight and Frequency
of Grafts .......................................................................................
2.7. Physicomechanical Properties......................................................
2.8. Characterization of Graft Copolymers.........................................
2.9. Applications..................................................................................
446
447
448
460
460
461
462
465
468
470
3. CONCLUDING REMARKS ................................................................. 474
LIST OF ACRONYMS ......................................................................... 474
REFERENCES ....................................................................................... 475
*To whom correspondence should be addressed.
445
Copyright  1999 by Marcel Dekker, Inc.
www.dekker.com
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ATHAWALE AND RATHI
1. INTRODUCTION
A graft copolymer is a polymer of molecules with one or more species of
block connected to the main chain as a side chain(s); these side chains have
constitutional or configurational features that differ from those in the main
chain. In the graft copolymer, the distinguishing feature of the side chains is
constitutional, that is, the side chains comprise units derived from at least one
species of the monomer different from those which supply the units of the main
chain [1].
The simplest case of a graft copolymer can be represented as : poly(A)-graftpoly(B), where the monomer named first (A in this case) supplies the backbone
(main-chain) units, while that named second (B) is in the side chain.
An approach to chemically bonded natural-synthetic copolymer compositions
is through graft polymerization. Grafting has been utilized as an important technique for modifying the chemical and physical properties of the polymer. Graft
copolymers are assuming increasing importance because of their tremendous
industrial potential. Some of the graft copolymers with high commercial utility
are (a) acrylonitrile-butadiene-styrene (ABS) (a graft copolymer obtained by
grafting polyacrylonitrile and polystyrene onto polybutadiene); (b) alkali-treated
cellulose-graft-polyacrylonitrile and starch-graft-polyacrylonitrile, which are
used as “superabsorbents” in diapers, sanitary napkins, and the like; and (c)
high-impact polystyrene (i.e., polystyrene-graft-polystyrene) copolymer.
Grafting technique has received considerable attention from scientists all over
the world, especially regarding those systems in which the natural polymer is
starch, probably due to its abundant availability at a very low cost. Its constant
price level over many years is impressive and makes it especially attractive as
an industrial raw material.
2. REVIEW PROFILE OF STARCH GRAFT COPOLYMERS
Starch, a high molecular weight polymer composed of repeating 1,4-α-Dglucopyranosyl units (anhydroglucose unit [AGU]) is generally a mixture of
linear and branched components, namely, amylose and amylopectin. Starch has
been used as a model substrate for graft investigations mainly because of the
ease with which vinyl monomers undergo grafting onto it. The forthcoming
interest in this field of chemistry is manifested in the increasing number of
publications in the last 15 years that highlight the different outstanding properties of these copolymers. Some of them are useful candidates that have commercial importance as hydrogels, flocculants, ion exchangers, and so on.
The present article summarizes the research work in the field of graft polymerization of vinyl monomers onto starch; some facets of this material compiled
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447
here have been treated under different aspects by different authors. Fanta and
Doane [2] published an excellent review on starch graft copolymers, principally
on acrylonitrile (ACN) and water-soluble vinyl monomers. Chinnaswamy and
Hanna’s review [3] on extrusion grafting starch onto vinylic polymers outlines
the rationale behind starch-based thermoplastic resin production. Many reviews
[4–13] are also available on the characteristics and trends in development of
applications of water-absorbing starch graft copolymers.
In contrast with the earlier reviews, the current review specifically covers the
reaction chemistry involved in graft polymerization of vinyl monomers onto
starch.
2.1. Grafting Parameters
The compositional parameters of this type of copolymer are usually expressed on a weight basis as follows [14–16]:
Total weight of polymer produced
(i.e., grafted plus homopolymer)
Monomer conversion (%) =
× 100
Weight of monomer charged
Grafting ratio (%) =
Weight of grafted polymer
× 100
Weight of starch
Grafting efficiency (%) =
Weight of grafted polymer
× 100
Weight of grafted polymer
plus homopolymer
(1)
(2)
(3)
or
=
Weight of grafted polymer
× 100
Weight of monomer charged
Add-on or grafting (%) =
Homopolymer (%) =
Weight of grafted polymer
× 100
Weight of copolymer sample
Weight of homopolymer
× 100
Total weight of polymer produced
(i.e., grafted polymer plus homopolymer)
or
(4)
(5)
(6)
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=
ATHAWALE AND RATHI
Weight of homopolymer
× 100
Weight of monomer charged
(7)
From the literature survey, it can be seen that a variety of formulas exist for
studying the copolymer composition and related parameters. However, grafting
efficiency and add-on/grafting (%) are the most important parameters that completely describe the copolymer system. Unfortunately, different authors use different equations to calculate these parameters (Eqs. 3–7), and there is a need
for uniformity. We personally feel that, during the graft polymerization reaction,
the homopolymer formation is a side reaction; hence it should not be used in
the determination of grafting efficiency GE of a monomer as a true picture is
not revealed, and one obtains higher values using Eq. 3. Therefore, we think
that Eq. 4 rather than Eq. 3 should be preferred.
2.2. Syntheses of Starch Graft Copolymers
As the interest in graft copolymers has increased over the years owing to
their multifaceted applications in many domains, a large variety of methods has
been developed for their syntheses.
Graft polymerization results in the formation of an active site at a point on a
substrate polymer molecule except at its end, and its exposure to a second monomer. Most graft copolymers are formed by radical polymerization. The major
activation reaction is chain transfer to a substrate polymer. In many instances,
the transfer reaction involves abstraction of a hydrogen atom. Ultraviolet or
ionizing radiation or redox initiation, among other methods, can also be used to
produce the polymer radicals that lead to graft copolymers.
In the following text, various systems used in graft polymerization of vinyl
monomers onto starch are discussed.
2.2.1. Ceric Ion Initiation
Mino and Kazerman [17] found that certain ceric salts [Ce(IV)], such as the
nitrate and sulfate, form very effective redox systems in the presence of organic
reducing agents such as alcohols, thiols, glycols, aldehydes, and amines. The
oxidation-reduction produces cerous [Ce(III)] ions and transient free-radical species capable of initiating vinyl polymerization.
Duke and coworkers [18, 19] have shown that ceric salts form complexes
with alcohols and glycols, and that the disproportionation of these complexes is
the rate-determining step of the oxidation-reduction reaction. In the case of alcohols, the mechanism of the initiation reaction can be written quite generally as
follows:
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Ce 4+ + RCH2OH
K
Kd
B
449
•
> Ce 3+ + H + + RCHOH (or RCH2O?)
where B represents the ceric complexes, and K and Kd are reaction constants.
The most important feature of the oxidation with ceric ion is that it proceeds
via single electron transfer with the formation of free radicals on the reducing
agent. Thus, if the reducing agent is a polymeric substrate such as starch, cellulose, or polyvinyl alcohol, and the oxidation is carried out in the presence of
vinyl monomer, the free radical produced on the substrate molecule (backbone)
initiates polymerization to produce a graft copolymer. This method of grafting
yields substantially pure graft copolymers since the free radicals are produced
exclusively on the backbone. An added advantage of this method is that it proceeds in a quite facile manner even at ambient temperature.
A number of investigations of graft polymerization onto starch have been
made using ceric ion initiator. Modified starches that had been reduced in molecular weight by acid, hypochlorite, or enzyme treatment were subjected to
graft polymerization of ACN using ceric ammonium nitrate (CAN) as initiator
[20]. With highly soluble starch, much of the starting material was recovered as
ungrafted carbohydrate, and the reaction product was largely soluble in dimethyl
formamide with a high poly(ACN) content. Fanta, Burr, and Doane [21] investigated the ceric-initiated polymerization of methyl methacrylate (MMA) onto
poly(ACN) with carbohydrate end groups and reported the formation of ACNMMA graft copolymer rather than the expected ACN-MMA block copolymer.
The evidence for the graft copolymer structure also was presented.
Employing Ce4+ initiator, styrene and ACN were graft polymerized onto
starch to give starch-graft-poly(ACN-co-styrene) copolymer, even though styrene alone does not graft onto starch [22]. The graft polymerization was attributed to the formation of ACN-styrene radicals, followed by copolymerization
with styrene.
Vazquez et al. [23] studied the Ce4+ consumption in the graft polymerization
of alkyl methacrylate (alkyl = methyl, ethyl, or butyl) mixtures with methacrylonitrile. The Ce4+ consumption increased with increasing mole fraction of the
methacrylate in the monomer feed and by increasing the alkyl group length of
the methacrylate, but in no case was the consumption total.
The optimum conditions for graft polymerization of some vinyl monomers
onto starch using Ce4+ initiator are given in Table 1.
Styrene, α-methyl styrene, 4-vinyl pyridine, and ethyl vinyl ether do not graft
polymerize onto starch in the presence of Ce4+ initiator at ambient temperature
[31]. Water-soluble monomers (namely, acrylamide, methacrylamide, acrylic
acid [AA], methacrylic acid, etc.) show a very low grafting percentage using
Ce4+ initiator. These monomers probably require a different initiating system
and/or different reaction conditions.
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ATHAWALE AND RATHI
TABLE 1
Optimum Conditions for Graft Polymerization of Some Vinyl Monomers onto
Starch Using Ce4+ Initiator
Monomer concentration,
mol/L
Acrylic acid,a 0.769
Methyl methacrylate, 0.400
Methyl methacrylate, 0.100
Ethyl methacrylate, 0.210
Butyl methacrylate, 0.220
Methacryl amide, 0.118
Ethyl acrylate (0.5–0.6)
Butyl acrylate, 1.105
N-Methylol acrylamide, 0.118
Vinyl acetate, 1.35
Acrylonitrile, 1–1.5
a
Ce4+,
mmol/L
Temperature,
°C
Time,
hours
Reference
no.
2.632
4.500
6.000
6.000
6.000
2.000
10–12
8.800
6.000
7.500
5.0–7.5
40
30–40
40
40
40
30
40
55
45
50
20–30
2
4
3
3
3
3
3
3
3
1.5–2
—
24
25
26
26
26
27
28
28
14
29
30
Starch pretreatment temperature 85°C.
2.2.2. Persulfate Initiation
Generally, ammonium persulfate or potassium persulfate are used as initiators for graft polymerizations. When an aqueous solution of persulfate is heated,
it decomposes to yield sulfate radical along with the other free-radical species.
The mechanism for grafting is [32]
S2O 8−?
SO 4−? + H2O
2HO •
HO • + HOOH
> 2SO 4−?
> HSO4 + HO ?
> HOOH
> H2O + HO •2
S2O 8−? + HO •2
> HSO −4 + SO 4−? + O2
St− OH + R •
> St− O • + RH
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St− O • + CH2=CH → St− O− CH 2−HC •
*
*
X
X
Monomer molecules
> Graft copolymer
where St− OH = starch, R • = free-radical species such as HO • and HO •2.
Starch-g-polystyrene copolymer was prepared by heating a semisolid mixture
containing starch and styrene and an aqueous solution of K2S2O8 [33]. The polymerization took place through the starch granular matrix, as well as on the
surface, and the maintenance of birefringence after graft polymerization suggested that grafting took place in amorphous regions of the granule. Starch-gpoly(N-methylol acrylamide–methacrylic acid) cation exchange composites
were synthesized by polymerizing the highly concentrated mixture using ammonium peroxydisulfate as initiator and with different reductants, such as sodium
thiosulfate, sodium pyrosulfite, and glucose [34]. Sodium thiosulfate was the
best reductant to produce the composite at the lowest solidification time and the
highest insoluble yield and carboxyl content.
The optimum conditions for graft polymerization of some vinyl monomers
using persulfate as the initiator are given in Table 2.
TABLE 2
Optimum Conditions for Graft Polymerization of Some Vinyl Monomers onto
Starch Using Persulfate Initiator
Monomer concentration,
mol/L
Acrylic acid,a 2.5–5.0
Methyl methacrylate
Butyl methacrylateb
Ethyl acrylate, 0.45–1.0
Butyl acrylate, 0.97
a
b
Initiator
concentration
mmol/L
(NH4)2S2O8
3.0
K2S2O8
8.0
K2S2O8-Na2S2O3
(3.0–4.0)-(2.0)
K2S2O8
6.36–8.17
(NH4)2S2O8
0.91
Solid-liquid ratio 2:100.
Starch concentration 4%; pH = 7.
Temperature,
°C
Time,
hours
Reference
no.
—
—
35
40
4
36
60
6
37
—
—
39
68
3
38
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ATHAWALE AND RATHI
2.2.3. Fe2+-Hydrogen Peroxide Initiation
As in the other systems in which grafting is accomplished via free-radical
reactions, in the case of Fe2+-H2O2 system it also may be presumed to involve
formation of radical sites on the backbone polymer.
The possible steps in the grafting process are [40]
H2O2 + Fe +2 → HO • + OH − + Fe +3
HO • + M
> M•
M • + n − 1M
HO • + Starch−H
> M •n
> Starch • + H2O
M •n + Starch−H → Starch • + MnH
Starch • + M
> Starch−M •
Starch−M • + n-1M
> Graft copolymer
where M = monomer.
Mixtures of acrylamide (AM) and dimethylaminoethyl methacrylate nitric
acid salt were graft copolymerized onto swollen and unswollen wheat starch
with ferrous ammonium sulfate–hydrogen peroxide initiation [41]. Polymer
grafted on swollen starch granules contained a higher dimethylaminoethyl methacrylate content than that grafted on unswollen starch because of the effect of
granule swelling on the graft copolymer structure, which could be minimized
by using 25–30% dimethylaminoethyl methacrylate in the monomer mixture.
Long poly(MMA) side chains attached to the starch at infrequent intervals
were obtained in graft copolymers prepared by initiation of MMA with H2O2
and an activator [42]. The grafting frequency was about one side chain per
230–250 glucose units in starch. Oxidized starch showed more frequent grafting
than unmodified starch. The effects of initiator/activator level and the gradual
addition of monomer and inhibitor have also been studied.
Vazquez et al. [43] studied the graft polymerization of methacrylic acid onto
potato starch using an H2O2-(NH4)2Fe(SO4)2 redox system and found that the
optimum graft yield was obtained at 7.3 × 10−3 mol/L H2O2 concentration. Grafting was also favored by increasing the monomer concentration and reaction
time.
2.2.4. Manganese Initiation
Mn4+ (as MnO2 from a KMnO4-acid system) and Mn3+ (as manganic pyrophosphate) have been employed for graft polymerization of vinyl monomers
onto starch.
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2.2.4.1. Mechanism of Grafting Using Mn4+ Initiator [44]. Starch is generally immersed in KMnO4 solution to deposit MnO2 on it. In the presence of
acid, formation of primary radical species occurs as a result of the action of the
acid on the deposited MnO2. Hence, different primary radical species are created
depending on the type and nature of the acid used. The initiation has been
explained using different acids as follows.
In the case of oxalic acid, the carboxyl radical ions constitute the primary
radical species and are possibly formed as given below:
Mn 4+ + C2O 42−
Mn 4+ + •COO −
Mn 3+ + 2C2O 42−
Mn 3+ + C2O 42−
Mn 3+ + •COO −
Measurable
Rapid
> Mn 3+ + CO2
Rapid
[Mn(C2O4)2] −1
Measurable
Rapid
> Mn 3+ + CO2 + •COO −
> Mn 2+ + •COO + CO2
> Mn 2+ + CO2
(8)
(9)
(10)
(11)
(12)
In the case of tartaric acid, creation of primary radical species occurs most
probably according to the reaction mechanisms suggested by Equations 13
and 14.
•
CH(OH)− COOH
Mn 4+ + *
CH(OH)− COOH
Slow
•
CH(OH)
Mn + *
CH(OH)− COOH
4+
Fast
CH(OH)
*
> CH(OH)− COOH + Mn 3+
+ CO2 + H +
(13)
CHO
> *
CH(OH)− COOH + Mn 3+ + H + (14)
and, in the case of citric acid, similar mechanisms are suggested:
CH− COOH
*
Mn 4+ + CH(OH)− COOH
*
CH− COOH
•
C− COOH
*
2+
+
> CH(OH)− COOH + Mn + 2H
*
•
C− COOH
(15)
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ATHAWALE AND RATHI
With respect to sulfuric acid, it appears that sulfate ion is oxidized by fresh
MnO2 to produce the sulfate ion radical, which acts as the primary radical species.
Mn 4+ + H2SO4
>
•
SO −4 + Mn 3+ + 2H +
(16)
Other free-radical species, namely, the hydroxyl radical, may also be formed:
Mn 4+ + H2O
> Mn 3+ + H ++ •OH
(17)
Once the free-radical species R • are created, they produce starch macroradicals via direct abstraction of hydrogen atom from the hydroxyl groups of the
starch molecules. This reaction may be represented as follows:
St− OH + R •
> St− O • + RH
(18)
where St− OH represents the starch molecule.
Starch macroradicals may also be formed by direct attack of Mn4+ or Mn3+
ions on starch molecule via abstraction of hydrogen atom.
St− OH + Mn 4+
> St− O • + Mn 3+ + H +
(19)
St− OH + Mn 3+
> St− O • + Mn 2+ + H +
(20)
In the presence of vinyl monomer, the starch macroradical is added to the
double bond of the vinyl monomer, resulting in a covalent bond between the
monomer and starch and the creation of free radical on the monomer (i.e., a
chain is initiated). Subsequent addition of monomer molecules to the initiated
chain propagates the grafting onto starch as shown by
H
*
St− O • + CH2= C
*
X
•
> St− O− CH2−C
*
X
H
*
St− O− CH2−C • + nCH2=C
*
*
X
X
> St− O−[CH2−CH]n
*
X
(21)
(22)
Termination of the growing grafted chain may occur via coupling, disproportionation, reaction with the initiator, and/or chain transfer.
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2.2.4.2. Grafting Mechanism of Manganic Pyrophosphate Initiator [45].
The following reaction mechanism has been presented to account for the synthesis of starch graft copolymers: Cleavage of the glycol groups of the AGUs in
amylose and amylopectin by manganic pyrophosphate, with the dissociation of
the glycol-Mn3+ complex considered as the rate-determining step:
Initiation:
Starch + [Mn(H2P2O7)3] 3−
> Starch-[Mn(H2P2O7)2] −complex
+ Mn(H2P2O7)2] 2−complex
>
Starch macroradical + H +
+ [Mn(H2P2O7)2] 2−
Propagation:
Starch macroradical + Monomer
> Starch graft copolymer
Termination:
(M)xM • + Mn +3
> Mn +2 + H + + Copolymer
Graft polymerization of ACN onto cassava starch gelatinized by alkali at
room temperature was studied using KMnO4 as the initiator in sulfuric acid
solution [46]. An 85% conversion of monomer and 95% grafting efficiency
were observed.
Hebeish et al. [47] grafted ACN onto rice starch in the presence of KMnO4
at 50°C; the graft yield, as percentage nitrogen, increased with increasing concentration of KMnO4 up to 25 ml, then leveled off within the range 30–60 ml
of KMnO4 solution, and the carboxyl content of the grafted starch increased
with increasing KMnO4 concentration. Increasing the ACN concentration up to
40% had no effect on graft yield, whereas a significant enhancement in grafting
could be achieved when an ACN concentration of 60% or greater was used.
Increasing the reaction time from 0.5 to 1.0 h was accompanied by a significant
increase in grafting. Practically no polymerization occurred at 20°C and 35°C,
although oxidation of starch occurred, as indicated by the creation of carboxyl
groups on the starch molecules.
Graft polymerization of AA onto rice starch using potassium permanganate/
acid (citric, tartaric, oxalic, and hydrochloric acid) was investigated [48]. The
dependence of the MnO2 amount deposited was related directly to the KMnO4
solution. The graft yield increased by increasing the concentration of acid to a
certain concentration beyond which grafting leveled off. The highest grafting
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yield was obtained with citric acid and the least with hydrochloric acid, with
intermediate yields for tartaric and oxalic acids. The more MnO2 deposited on
the starch, the higher was the graft yield. With the increase in the polymerization
temperature from 30°C to 50°C the graft yield increased, but at 60°C the yield
decreased.
The emulsion polymerization of styrene onto starch was investigated using
manganic pyrophosphate [Mn(H2P2O7)3]3− as the initiator and hexadecyl trimethyl ammonium bromide as the emulsifier [49]. The grafting percentage was
found to be 150%.
The Mn3+ initiation system was used to prepare ACN starch graft copolymer
[50]. Conversion of monomer, grafting ratio, and percentage add-on increased
with increasing amounts of monomer charged. The amount of homopolymer
formed was extremely low (,1%). The efficiency, measured as conversion, was
consistently higher with gelatinized starch as the substrate.
Manganic pyrophosphate initiated the graft polymerization of potato starch
with ACN and methyl acrylate (MA), although AM showed a tendency to homopolymerize. A reaction mechanism involving cleavage of glycol groups of
the AGUs and oxidation of carbonyl groups to yield oxidized starch has also
been proposed [45].
2.2.5. Irradiation
In addition to chemical methods of initiation, free radicals on the starch backbone can be produced with both 60Co and electron beam irradiation [2]. Two
techniques have been used to initiate graft polymerization. In simultaneous irradiation, mixtures of starch and monomer are irradiated first, and the activated
starch is then allowed to react with monomer. Low temperature, low moisture
content, and exclusion of oxygen increase free-radical stability; under favorable
conditions, a significant percentage of the free radicals in irradiated starch still
can be detected by electron spin resonance even after a number of days at room
temperature. Preirradiation often produces less homopolymer than simultaneous
irradiation since monomer is absent during the irradiation step. With simultaneous irradiation, however, there is a better opportunity for the reaction of shortlived free radicals with monomer. Irradiated starch has also been allowed to
react with oxygen to form hydroperoxy groups, and graft polymerization is then
initiated by reaction of the activated starch with a reducing agent, such as ferrous sulfate.
A mixture of AM and 2-acrylamido-2-methyl propanesulfonic acid was
grafted on starch by γ-irradiation [51]. In the grafting, the conversion of the
monomers to graft copolymer was nearly quantitative when pregelatinized
wheat starch was irradiated simultaneously.
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The grafting of AA to starch was investigated with γ-preirradiated starch and
an aqueous solution of AA [52]. The rate of grafting increased initially with
time, then decreased, and approached zero when the percentage of grafting
reached a maximum. At a given radiation dose, the rate of grafting was proportional to the first power of the concentration of irradiated starch and to the 1.5
power of the initial concentration of AA.
Styrene and MA were grafted onto wheat starch by γ-radiation and chemical
initiation, respectively, giving a 54:46 starch-graft-polystyrene copolymer and a
55:45 starch-graft-poly(methyl acrylate) copolymer [53]. In the polymerization,
68% of styrene and 41% of MA were grafted onto starch.
2.2.6. Miscellaneous Initiation Systems
Besides the five chief grafting processes described above, a number of ways
of synthesizing starch graft copolymers have been developed that are not easy
to classify unambiguously.
The anionic graft polymerization [54] of lauryl methacrylate on the potassium alkoxide derivative of starch gave increasing graft yields with increasing
alkoxide concentration. With increasing monomer concentration and temperature, the extent of poly(lauryl methacrylate) formed increases. The graft polymer
composition depended on the reaction conditions; graft polymers containing 30–
65% poly(lauryl methacrylate) were obtained.
The anionic grafting of methacrylonitrile on starch in dimethyl sulfoxide,
initiated by the lithium and sodium alkoxide derivatives, has been studied [55].
The results were compared with those obtained previously with potassium alkoxide. With lithium, the results were not highly reproducible, but with sodium
the results were reproducible, as indicated by the monomer-starch balance at the
end of the polymerization. The yield of pure graft polymer with different alkoxides was in the order potassium > sodium > lithium; lower alkoxide concentrations were required for attaining complete conversion and optimal yield in the
case of potassium alkoxide.
Using metal acetylacetonate complexes M(acac)n (M = manganese, cobalt, or
chromium, and n = 3; M = V, n = 2) MMA, ACN, AM, and AA were grafted
onto starch [56]. Highest grafting yields were obtained in the case of Mn(acac)3.
MMA has been grafted onto starch using copper acetylacetonate–trichloroacetic acid as the initiator system [57]. The grafting percentage G and grafting
efficiency GE increased with increasing copper acetylacetonate concentration
up to 7.0 × 10−3 mol/L and then decrease. The values of G and GE were maximum at an MMA concentration of 0.805 mol/L. The values of G and GE were
maximum at a starch concentration of 0.220 mol/L and 0.309 mol/L, respectively, when other reaction conditions were kept constant. The suitable trichloroacetic concentration for the grafting system was 5.0 × 10−3 mol/L.
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Photograft polymerization of ACN on potato starch using potassium peroxyvanadate (KVO4) as a photoinitiator in neutral aqueous methanolic media at
32°C has been studied [58]. A 100% grafting efficiency with no homopolymer
formation was observed. Maximum conversion and grafting were obtained for
a concentration of about 2:3 methanol-water (vol/vol). The initiation of graft
polymerization was probably a consequence of direct oxidation of starch macromolecules into starch macroradicals by V7+, which was the consequential oxidizing species in the pervanadate solution. Termination was mostly due to a combination of growing chain with starch macroradicals.
MMA has also been grafted onto potato starch in a methanol-water mixture
in the presence of KVO4 under visible light [59]. The highest grafting (,95%)
and total conversion (,85%) were obtained when polymerization was carried
out using methanol-water mixture at a 0.96:1 ratio, 0.5 × 10 2 mol/L KVO4, and
2 ml MMA. The grafting percentage decreased with increasing starch content,
and the total conversion passed through a maximum when the starch quantity
was 1.7 g.
The H2O2/FeSO4/thiourea dioxide (TUD) redox system has been used effectively as an initiator system for grafting glycidyl methacrylate onto starch [60].
The graft polymerization of AM onto starch using a CS2–ferrous ammonium
sulfate–K2S2O8 redox system has been investigated under different reaction conditions, including alkali concentration in the pre-CS2, K2S2O8 concentration, ferrous ion concentration, monomer concentration, pH of the polymerization medium, polymerization temperature, use of a solvent-water mixture instead of
aqueous medium, and the liquor ration [61]. The effect of the rate of thiocarbonation on the magnitude of grafting of AM onto starch was studied with respect
to K2S2O8 and ferrous ion concentration. The graft yield was favored significantly in acidic medium, as well as by increasing the persulfate concentration,
AM concentration, and polymerization temperature. CCl4 was the best medium
for polymerization. AM has been grafted onto cornstarch by a hydrogen peroxide–thiourea (TU) initiation system [62]. The monomer conversion Cm, grafting
percentage G, and grafting efficiency GE were affected considerably by [H2O2],
[TU], [AM], pH value, temperature, and polymerization time. Good Cm, G, and
GE were obtained at [H2O2] = 1.6 × 10−3 mol/L, [TU] = 8 × 10−4 mol/L, [AM] =
1.0 mol/L, pH = 5, and 5 h at 45°C.
MMA and 4-vinyl pyridine have been grafted onto starch using acetic acid–
H2O2 at 60°C; however, along with the graft copolymer, a considerable amount
of homopolymer formation was observed [63]. Benzoyl peroxide and azo-bisisobutyronitrile have been used as initiators for grafting ACN and MA [64]. The
degree of grafting of vinyl monomers onto starch depended on the radical initiator concentration, monomer concentration, time, and temperature. The relative
reactivities of monomers used were ACN > MA.
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The reaction of MMA with potato starch in a methanol-water mixture in the
presence of potassium trioxalato manganate and in the absence of visible light
gave the corresponding graft copolymer [65]. The highest grafting percentage
G (,95%) was obtained when polymerization was carried out at 35°C using
the methanol-water mixture in a 2.19:1 ratio and 10.5 × 10−4 mol/L. The G and
total conversion TC increased with increasing polymerization time up to 120
min and then levelled off, whereas grafting efficiency remained steady at
,80%. The TC also increased with increasing MMA concentration, and P decreased with increasing amount of starch.
Potassium bromate–TUD redox initiating system has been used to graft polymerize AA onto native and hydrolyzed cornstarches [66]. The optimum conditions for the graft copolymer formation were with native starch (NS):[KBrO3] =
6 mmol/100 g (NS), AA, 30%, polymerization temperature 40°C, and polymerization time 30 min. Whistler and Goatley [67] obtained starch-graft-polyacrylamide copolymer by ball milling cornstarch along with AM.
2.2.7. Grafting Efficiency of Initiators
The efficiency of different metal salt initiators such as ceric ammonium nitrate, ferrous sulfate–hydrogen peroxide, and manganese phosphate in graft
polymerization of ACN on potato starch has been investigated [68]. The highest
grafting degree (83–95%) was obtained when the cerium salt was used as the
initiator. The kind of initiator used considerably affected the viscosity of the
aqueous solution of saponified starch-graft-poly(ACN). Similar results were observed by Feng and Wu [69] during the graft polymerization of AM onto starch,
and the grafting yield was found to decrease in the order ceric ammonium nitrate
> KMnO4 > H2O2-Fe2+.
Brzozowski and Noniewicz [70] compared the yield of starch-graft-polyacrylamide using Na2S2O8, KMnO4, Ce(SO4)2?4H2O, and a system consisting of
Ce(SO4)2?4H2O + KMnO4 as the initiator. The last system was the most effective; the yield of grafting was up to 70%.
The graft polymerization of AM onto starch, initiated by the Ce4+-S2O 8−2 binary system, has been studied and compared with those using ceric or persulfate
initiator [71]. The Ce3+ formed during graft polymerization was reoxidized back
to Ce4+ by S2O 8−2 in situ to achieve a Ce4+ → Ce3+ → Ce4+ cycle that led to cyclic
use of Ce4+ ions and the decrease of the initial concentrations of Ce4+.
Trimnell, Fanta, and Salch [72] compared the ability of Fe2+-H2O2 and ceric
initiating systems to graft polymerize methyl acrylate on to granular starch. In
the case of Fe2+-H2O2, a significant amount of acetone-extractable MA homopolymer was produced, while CAN gave quantitative conversions of MA to
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graft copolymer with a low homopolymer percentage. The authors have attributed this to the difference between Fe2+-H2O2 and CAN initiation mechanisms.
The efficiencies of three initiators—potassium persulfate, iron (2+)–hydrogen
peroxide, and potassium permanganate—in grafting AM on to starch have been
studied [73]. KMnO4 gave the best grafting efficiency compared to the other
initiators. The graft polymerization of AM on to rice starch was investigated
under different reaction conditions using K2S2O8, benzoyl peroxide (Bz2O2), and
KMnO4 as the initiators [31]. Under those conditions, grafting was characterized
by two stages regardless of the initiator used. The rates of grafting exhibited the
order of the efficiency of the initiators as K2S2O8 > Bz2O2 > KMnO4. Substantial
differences in solubility were observed between the graft copolymer and unmodified starch, as well as among the copolymers prepared using the three initiators.
Gao et al. [74] claim that a manganese (VII)–TU redox system is the best
among such other initiators as Fe(III)-TU, V(V)-TU, Cr(VI)-TU for grafting ACN onto starch. They further pointed out that acids played an important
role in grafting, and the order of their influence was found to be HClO4 >
H2SO4 > HCl.
2.3. Evidence for Grafting
In general, due to the lack of solubility of the graft copolymers in most of
the common organic solvents, the nuclear magnetic resonance (NMR) technique
cannot be used. However, the confirmation of the graft copolymer can be obtained indirectly by the acid hydrolysis technique, in conjunction with infrared
spectroscopy, and in a few cases by 13C-NMR spectroscopy.
The appearance of the characteristic bands of starch and the grafted polymer
in the infrared (IR) spectrum is taken as the prime evidence [14, 26, 27, 30].
However, this technique cannot be applied to those copolymers for which the
bands merge such as starch-g-polyacrylamide, starch-g-poly(N-methylol acrylamide), and the like. In such cases, help is sought from the acid hydrolysis
method, by which one can indirectly, but unambiguously, conclude the graft
copolymer formation. During acid hydrolysis, starch hydrolyzes, and the grafted
chains are isolated. Generally, 1 N HCl is preferred to hydrolyze selectively
starch without affecting the grafts. The purified isolated chains are identified
and confirmed from IR spectroscopy.
2.4. Monomer Reactivity
Employing ceric ammonium sulfate as the initiator for graft polymerization,
Nagaty, Mouti, and Mansour [75] studied the reactivity of three vinyl monomers
toward grafting onto starch and found that the order of reactivity was ACN >
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ethyl acrylate > MMA. Similar observations have been reported in the case of
graft polymerizations of ethyl acrylate and ACN onto starch [76].
Khalil, Mostafa, and Hebeish [77], by varying the reaction conditions that
included the persulfate and monomer concentration, polymerization time and
temperature, and liquor ratio, obtained the optimum conditions for grafting different vinyl monomers onto starch. The AM showed the highest grafting ability,
AA the lowest, and intermediate abilities were shown by ACN and methacrylic
acid.
Reyes et al. [52], in their study of graft polymerization of vinyl monomers in
aqueous medium using CAN as the initiator, reported that the grafting efficiency
decreased with the decrease in polarity in the order ACN > AA > MMA > vinyl
acetate (VAc) > styrene. Misra et al. [64] initiated graft polymerization of ACN
and MA onto starch employing benzoyl peroxide in aqueous medium; they reported that the former shows higher grafting efficiency compared to the latter
and attributed this to the greater polarity and solubility of ACN over MA. However, it was found that some vinyl monomers, in spite of having comparable
polarity/solubility, showed a very large difference in their grafting percentage.
A study [31] suggested that the results of Reyes et al. [52] and Misra et al. [65]
(i.e., the greater the polarity and solubility of the vinyl monomer is, the greater
will be the grafting) are mere generalizations based on the experiments carried
out on a few selected monomers. There do not necessarily exist any hard and
fast rule correlating the polarity and solubility of vinyl monomer and its ability
to graft polymerize.
Gao et al. [74] concluded that, in graft polymerization using the Mn(VII)TU system, the grafting capability of the different monomers was MMA > AN
> AM > AA.
2.5. Kinetics of Graft Polymerization
Gugliemelli, Swanson, and Doane [78] studied the kinetics of grafting ACN
onto starch. The polymerization rate was related directly to the square root of
the Ce(IV) concentration and to the 1.3 power of the ACN concentration.
The rate of graft polymerization of MMA in the presence of aqueous mixtures containing dibutyltin dilaurate (DBTL) and CuCl2 at 85°C increased with
the first power of DBTL concentration and with the 1.3 power of MMA concentration [79].
Graft polymerization of 2-hydroxyethyl methacrylate and ethylene dimethacrylate onto starch using ceric (IV) as an initiator has been investigated [80].
The rate of graft polymerization had a first-order dependence on the monomer
concentration, suggesting that grafting followed typical free-radical polymerization kinetics. Similar results have been reported by Egboh and Jinadu [81] in
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the case of graft polymerization of MMA onto starch in the presence of CAN
as the initiator.
A kinetic study was made of the CAN-initiated graft polymerization of MA
onto potato starch (S) [82]. From the experimental results, a radical mechanism
was propounded, and a new kinetic equation of the graft polymerization was
established as Rp-Kdd [CAN] + Kkpkd /kt[S][[MA], where K, kd, kp, and kt are polymerization, dissociation, propagation, and termination constants, respectively.
Pan et al. [83] studied the kinetics of graft polymerization of AM onto starch.
The rate of reaction Rp and average degree of polymerization Xs were expressed
as follows:
Rp = Kpd −E/RT [Mn 7+] 0.5 [S] 0.5 [H2SO4] 1.0 [AM] 1.0,
and
X s = K [AM] 1.0/{[Mn 7+] 0.5 [S] 0.5 H2SO4] 1.0}
By determining the rate of graft polymerization at different temperatures,
the authors calculated the activation energy value E = 23.8 kJ/mol. This study
confirmed that starch is a basic material taking part in chain initiation, and that
termination is essentially a biradical reaction.
The kinetics of grafting ACN onto starch by manganic pyrophosphate initiation has been studied [84]. The rate equation of the grafting was derived, and
the apparent rate constant and the activation energy were determined as 3.37 ×
10 2 L/mol and 25.90 kJ/mol, respectively.
The expression of polymerization rate [85], obtained from the graft polymerization of MMA onto starch using acetyl acetonate as the initiator, was expressed
as Rg = K [Initiator]1/2 [Starch]1/2 [MMA]. The activation energy of graft polymerization was found to be 59.2 kJ/mol.
2.6. Copolymer Composition:
Molecular Weight and Frequency of Grafts
Grafted polymer is generally separated from the starch backbone by the acid
hydrolysis technique. In the acid hydrolysis technique, the graft copolymer is
refluxed in a 1 N HCl solution to hydrolyze starch, and the separated grafts are
purified. The average molecular weight is determined, providing the basis for
calculation of the frequency of the AGU graft:
AGU/Graft = Mn of grafted polymer × (wt% of starch in graft copolymer/
Wt% of grafted polymer) × (1/162)
where 162 = molecular weight of the AGU repeating unit, and wt% of starch +
wt% of grafted polymer = 100.
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Effects of reaction conditions such as temperature (2°C and 50°C), concentration of initiator, and addition order of initiator and monomer on both grafting
frequency and molecular weight of grafted polyacrylonitrile have been studied
for the reaction of gelatinized wheat starch with ACN initiated by CAN [86].
The method of addition of initiator and monomer and the fivefold increase in
the amount of CAN had no effect on the composition of the graft copolymer.
The major fraction, which was insoluble in dimethyl sulfoxide, had a frequency
of 3920 AGU/graft and a molecular weight of 655,000 for grafted polyacrylonitrile. The failure of increased amounts of ceric ions to produce more grafted
chains was because of the further reaction of free radicals on the starch backbone with excess ceric ion to yield oxidized products incapable of initiating
polyermization. In short, the excess ceric ion competes with monomer molecules
to reach the free-radical site on the starch backbone and consume it faster than
the monomer molecules. Consequently, there is no increase in grafting percentage.
Whistler and Goatley [67] have found that the polyacrylamide obtained from
acid hydrolysis of starch-g-polyacrylamide copolymer had an osmotic molecular
weight of 84,000.
The Ma values for polyacrylonitrile were found to be 4000–90,000, and the
frequencies of attachment of side chains ranged from 300 to 1100 AGU/graft
chain [87].
The influence of various chain modifiers on both the molecular weight of
grafted polyacrylonitrile and the grafting frequency of the starch-g-polyacrylonitrile copolymer has been investigated [88]. No significant grafting was observed
when ethyl mercaptan, ethyl acetate, and chloroform were used, while considerable grafting occurred with 1-dodecanethiol. Acetaldehyde gave some chain
shortening, but the product had a higher graft frequency. The use of 4.97 × 10−3
and 4.97 × 10−2 mol/L Cu(NO3)2?3H2O gave products with 5075 and 10,000
AGU/graft, respectively, while the use of 4.97 × 10−3 mol/L of Cu(OAc)2?3H2O
gave a product with a grafting frequency of 19,300 AGU/graft and a reduced
molecular weight. In the presence of CuCl2?2H2O, a 10-fold reduction in the
molecular weight of the grafted poly(ACN) was observed.
Tahan and Zilkha [89] have shown that, by anionic graft polymerization of
methacrylonitrile, it is possible to obtain graft copolymers having more densely
packed grafted side chains of relatively low molecular weight than those obtained by free-radical graft polymerization. The effect of starch granule swelling
on graft copolymer composition was studied using seven monomers varying
widely in water solubility and ionic charge [90]. ACN and AM gave higher
molecular weight products and less frequent graft with swollen starch than with
unswollen starch, while methyl methacrylate, N,N-dimethyl aminoethyl methacrylate (HNO3 adduct), N-tert-butylaminoethyl methacrylate (HNO3 adduct),
and [2-hydroxy-3-(methacryloyloxy)propyl] trimethylammonium chloride gave
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less frequent grafts of higher molecular weight with swollen starch than with
unswollen starch. With acrylic acid, the graft molecular weight was independent
of starch granule swelling, although grafting was less frequent when using swollen starch.
The influence of swelling and disruption of the starch granules on the composition of starch-g-polyacrylonitrile copolymer has been studied [91]. Copolymers with a wide range of molecular weights and grafting frequencies were
obtained by varying the temperature at which starch was swollen. Shorter and
more frequent grafts were produced in unswollen granules. Starch swollen at
85°C gave extremely high molecular weight grafts and a completely disrupted
granular structure with increased solubility.
It has been reported that the influence of granule swelling on copolymer
composition is due to the faster termination rate for growing poly(ACN) chains
in unswollen starch [92].
Gugliemelli et al. [78], in their study of starch-g-poly(ACN) reported that the
Mn of poly(ACN) from gelatinized starch systems was about one order higher
than that from granular systems. The M was small at low temperature in the
granular system and decreased with increasing reaction time. In the gelatinized
system, Mn increased with time to a maximum and then decreased. Molecular
size dispersity values were 2–4 and 5–10 for poly(ACN) from the gelatinized
and granular starches, respectively.
In the grafting of MMA onto starch in the presence of manganic pyrophosphate at 30°C, the frequency of grafts decreased. The Mn grafts were of the
order 10 6 [93], while grafting ACN onto starch in the presence of manganic
pyrophosphate, the Mn and frequency of grafts increased by a factor of about 10
after swelling and gelation of starch [94]. An increase in the amount of starch
increased grafting frequency, obviously because of the availability of a large
number of substrate molecules for grafting with a consequent decrease in the
Mn of grafts.
The graft polymerization of ACN onto starch gelatinized in water at ≤94°C
gave less frequent grafting of higher molecular weight poly(ACN) than comparable graft polymers onto gelatinized starch [95].
Starch-g-poly(ACN) copolymer prepared in several aqueous-organic solvent
systems with CAN as the initiator had more graft chains and were of lower
molecular weights than those prepared in water alone [96]. Methanol:water
80:20 vol/vol produced grafted chains with a molecular weight of 15,700 and a
grafting frequency of 253 AGU/graft.
On grafting ACN onto starch in the presence of (NH4)Fe(SO4)2-H2O2, the
yield and conversion increased and the molecular weight of the graft decreased
with increasing concentration of ferrous ion and peroxide in the system [97].
The gelation of starch greatly reduced the grafting efficiency and the number of
grafting sites and increased the molecular weight of the grafted poly(ACN). The
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molecular weight increased considerably as the reaction in temperature increased. As the ratio of ACN to starch increased, the molecular weight of the
graft increased, while the number of grafting sites, the conversion, and the grafting efficiency remained constant. Mehrotra and Ranby [98] reported that, in
grafting ACN on potato starch in the presence of Na4P2O7 and Mn3+ ion formed
from acidic MnSO4 and KMnO4 at 30°C, the graft frequency (AGU/grafted
chain) and average molecular weight of grafts decreased when the Mn3+ ion
concentration was increased from 0.15 to 3.0 × 10−3 mol/L. The graft frequency
increased with increasing concentration ratio of starch to ACN during polymerization by a factor of 3.
2.7. Physicomechanical Properties
2.7.1. Water-Absorbing Property
In general, the graft copolymers prepared from gelatinized starch, rather than
granular starch, show very high water-absorbing properties. Of the various vinyl
monomers, chiefly ACN, AM, and AA have been frequently employed as the
grafting monomer to obtain superabsorbents.
A Japanese patent [99] describes the preparation of water-absorbing starch
graft copolymer as follows: cornstarch 25.0 g, ACN 100 g, and 15 g of CAN
in HNO3 were mixed in H2O at 35°C for 3 h to give 113.6 g starch graft copolymer, which was saponified with 66.9 g of NaOH at 90°C for 2 h, neutralized
with 30.1 g AA at room temperature, and mixed with 2.6 g H2O2 at 138°C–
145°C to give a film showing a water absorption of 823 g versus 87 g in the
absence of AA.
Starch-graft superabsorbents have been prepared by graft copolymerizing either with poly(ACN) and saponifying the resulting copolymer or with trimethyl
aminoethyl acrylate chloride and methylene bis-acrylamide as cross-linking
agent [100]. The water absorbency was found to decrease with an increase in
the cross-link density. It increased with the ionic content of the graft copolymer
up to a maximum; however, excess charges led to a decrease in swelling. The
swelling increased with increasing molecular weight of poly(ACN) up to 5 ×
10 5. In alkaline solution, the absorbency of both the ionic gels decreased significantly. However, in the presence of multivalent ions, their behavior was different. For cationic absorbents, the swelling was found to depend on the ionic
strength, but not on the ion valency. Anionic absorbents were affected significantly by multivalent cations.
Sulfonated saponified starch-g-poly(ACN) copolymers were prepared, and
their properties were compared with other water absorbents [101]. The absorption performance of different water absorbents decreased in the following order:
sulfonated saponified starch-g-poly(ACN) copolymer > saponified starch-g-
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poly(ACN) copolymer @ cross-linked starch-g-poly(AA) sodium salt copolymer
> sulfonated saponified starch-g-poly(AM) copolymer > saponified starch-gpoly(AM) copolymer > carboxymethyl starch. The water absorption of the
starch-g-poly(ACN) copolymer was dependent on the relative humidity, degree
of grafting, dispersion medium, pH of the solution, and heat pretreatment. The
starch-g-poly(ACN) copolymer showed good water retention properties at less
than 50°C.
A report also concerns the preparation of starch-g-poly(ACN) copolymer that
could absorb ≤ 2000 times of its weight of water (g/g) [46]. The graft copolymerization of ACN onto cassava starch, gelatinized by alkali at room temperature, was studied using KMnO4 as the initiator in H2SO4 solution. A water-absorptive resin has also been prepared from starch and ACN, it absorbed 500–1500
ml water per gram and 40–80 ml synthetic urine per gram copolymer [102].
The water absorbency of saponified starch-g-poly(ACN) copolymer films (prepared from gelatinized starch varieties) was 530–1200 g H2O per gram, depending on the type of starch [103], but the absorbency of the hydrolyzed and saponified grafted films was 600 g/g. The absorbency decreased significantly when
the films were heat treated at temperatures greater than or equal to 135°C.
Rodehed and Ranby [104] studied the structure and water-absorbing properties of starch-g-poly(ACN) hydrogels. The alkaline hydrolysis of the grafted
copolymer converted the nitrile groups to carboximide (,30%) and sodiumcarboxylate (,70%) groups. The swelling of the copolymer formed, which retained about 700 g water per gram of the dry copolymer, was studied in alcohol/
water mixtures of increasing alcohol content at 21°C, 31°C, and 41°C. The
liquid retention versus alcohol content indicated one minor transition for ethanol/water mixtures and two small transitions for methanol/water mixtures. The
main transition for both the alcohol/water mixtures was a collapse of the gel at
50–60 vol% ethanol and 60–70 vol% methanol, respectively. Increasing the
temperature from 21°C to 41°C increased the liquid retention and moved the
transition to higher alcohol concentrations by 5–10 vol%. When the starch copolymer was hydrolyzed in dilute mineral acid to remove the starch moiety, the
retention values increased by a factor of about 3 for both pure water and alcohol/
water mixtures. The retention-versus-methanol-concentration curves showed
three transitions that were similar to those of the starch copolymer before acid
hydrolysis.
Starch graft copolymer prepared from ACN and 2-acrylamido-2-methylpropanesulfonic acid (62.5:37.5 feed ratio) showed water absorbency of 580 g per
gram of copolymer [105]. Saponified starch-g-poly(ACN) copolymers, prepared
using (NH4)2Fe(SO4)2-H2O2 as the initiator system, showed water absorption of
80–440 ml/g and 20–70 ml synthetic urine [96], while the saponified starch-gpoly(ACN) copolymer prepared from persulfate initiator showed water absorption of 400–490 ml/g [106].
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Water-absorbent resin has also been prepared from hydrolyzed starch-g-poly(acrylamide-N,N-bis acrylamide) copolymer, which absorbed 100 times its original weight [107]. However, the presence of NaCl, ethanediol, propanetriol in
aqueous solution decreased its water absorbency. The maximum water absorption occurred at pH 3.5–8.5.
Epichlorohydrin cross-linked starch-g-poly(AA) sodium salt copolymer was
prepared using ammonium persulfate as an initiator. It absorbed deionized water
more than 1000 times its own weight [108].
2.7.2. Solubility/Swellability and Gelatinization
The solubility of starch graft copolymers synthesized from n-alkyl acrylates
and methacrylates (where alkyl = methyl, ethyl, buytl), N-methylol acrylamide,
methacrylic acid, and the like in various polar and nonpolar solvents was found
to be as negligible as that of the substrate material (viz., starch). However,
interestingly, dimethyl sulfoxide is a good solvent for starch, but the graft copolymers do not dissolve in it; even on heating, they just swell, indicating the
cross-linked nature of the starch graft copolymers. The cross-linking was probably due to chain combination of the growing graft molecules.
Starch gelatinizes in water at around 70°C. However, the graft copolymers
do not gelatinize even after heating at 100°C, which further confirms the crosslinking of starch graft copolymers [14, 109].
2.7.3. Mechanical Properties
The effect of water on starch-g-polystyrene and starch-g-poly(MA) extrudates was investigated [45]. Both the graft copolymers lost strength during soaking in water and regained their original tensile strength during drying. Starch-gpoly(MA) swelled in water and did not recover the original dimensions during
drying. The tensile and mechanical properties of the extruded and molded graft
copolymers have been reported, along with the plasticizing effect of water.
Swanson et al. [110] have reported that the ultimate tensile strength (UTS) of
starch-g-poly(MA) copolymer was affected adversely by high levels of grafted
poly(MA), high homopolymer content, and extended contact with HNO3-CAN
initiator. The molecular weight of the grafted side chains had no apparent effect
on UTS, and there was a drastic reduction in the tensile strength of graft copolymer on incorporation of 10% levels of polar solvents. It has also been reported
that the addition of 15 parts di-butyl phthalate or glycerol/100 parts starch-gpolystyrene reduced the ultimate tensile strength of the extruded polymer from
2.8 kg/mm 2 to 1.5 kg/mm 2 and 0.34 kg/mm 2, respectively, without significantly
affecting brittleness [33].
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Lim and Im [111] studied the structure and tensile properties of starch-gpoly(MA) films. They have reported that the tensile properties of the copolymers were reduced when stored at high relative humidity, which was attributed
to the plasticizing action of water molecules in the film. Crystallinities of copolymer films also gradually disappeared. Water molecules swelled amorphous
regions and then destructed relatively unstable crystalline regions in copolymer
films. Tensile properties of starch-g-poly(MA) copolymer films were dependent
on starch content and starch composition (the ratio of amylose vs. amylopectin).
Graft copolymer with rubbery poly(MA) and linear amylose showed lower tensile strength and higher elongation at break point.
Extrusion processing and tensile testing of ribbons of starch-g-poly(MA-coVAc) copolymer indicated that, although increasing amounts of VAc (≤30:70
VAc:MA) did not affect the extrudate formation, the presence of VAc increased
the brittleness over that for starch-g-(MA) graft copolymers [112].
A Japanese patent [113] describes a biodegradable polymer composition of
starch-g-poly(VAc) and linear low-density polyethylene (LDPE), which on extrusion showed a yield strength of 1.56 kg/mm 2, bursting strength of 2.31 kg/
mm, and elongation of 571% and complete breakdown after embedding in an
active soil for 100 days at 40°C. Tensile properties of starch-g-poly(MA) varied
with the method used for the initiator addition and also with the starch variety
used in graft polymerization [114]. Since water acts as a plasticizer for starch,
samples extruded at a high moisture content exhibited higher percentage elongation (%E) value than the same polymers extruded at low temperature. Values
for percentage elongation also increased with higher percentages of poly(MA)
in the graft copolymer. Another patent [115] describes moisture-shrinkable biaxially oriented films from starch-g-(MA) copolymers. The films are said to be
useful as shrink-wrapping materials and can be easily removed by soaking
briefly in water.
2.8. Characterization of Graft Copolymers
2.8.1. Infrared Spectroscopy
Infrared (IR) spectroscopy has been used extensively for the confirmation of
graft copolymer formation [49, 70, 72, 116–120].
The percentage of poly(ACN) graft chains in starch-g-poly(ACN) copolymer
was determined quantitatively by IR spectrometry, taking the 855 cm−1 characteristic absorption frequency as the internal standard peak and the 2245 cm−1
characteristic absorption frequency as the quantitative analysis peaks [121]. This
analysis method has the advantages of being easy to operate, high speed, microanalytic, and it has relatively high accuracy.
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469
13
C-NMR Spectroscopy
The starch graft copolymers, prepared from a mixture of methacrylonitrile
and C1-6 alklyl methacrylate, have been characterized by 13C-NMR spectroscopy
[117]. This method has also been used to analyze copolymers of hydrophobic
and hydrophilic polymethacrylates grafted on starches [122–124]. The grafted
chains were released by hydrolysis and analyzed. All the grafted chains were
syndiotactic, as expected from a radical initiation method. The syndiotacticity
increased slightly as the alkyl group of the methacrylate ester increased, indicating a steric hindrance effect on stereoregularity. Triad, tetrad, pentad, and hexad
signals were resolved.
The dynamic states of water and of the polymer were studied by two-dimensional heteronuclear 13C- 1H solid-state NMR spectroscopy [125]. The method
was demonstrated in the study of the hydration in hydrolyzed starch-g-poly(ACN) copolymer.
2.8.3. X-ray Diffraction and Scanning Electron Microscopy
Starch-g-poly(ACN) copolymer has been characterized by scanning electron
microscopy (SEM) and X-ray diffraction (XRD) [75, 124]. The granular size of
the graft copolymer was larger, the surface was rough, and the shape changed
compared with the ungrafted starch. The crystallinity of the graft copolymer
granules decreased. The SEM of starch-g-poly(ACN) showed that the poly(ACN) was grafted both on the surface and in the interior of the granule [127,
128]. At higher grafting ratios, the products contained increasing amounts of
grafts inside the granule, but the center of the granule was always hollow.
Starch-g-polyacrylamide copolymers have also been characterized by SEM
[118]. Graft copolymers of methyl methacrylate onto canna starch have been
characterized by SEM and XRD [119]. The X-ray diffraction patterns of starchg-polyacrylamide copolymers revealed their amorphous character regardless of
the grafting degree [70]. The X-ray powder diffraction study of starch and starch
graft copolymers from methyl-, ethyl-, and butylmethacrylate [26], and N-methylol acrylamide [14] also showed similar results, that is, grafting decreases the
crystallinity of starch. Starch showed four distinct crystalline peaks in the X-ray
diffractions, which merged into one on grafting.
2.8.4. Thermal Analysis
Starch-g-polyacrylamide showed thermal stability up to 200°C–250°C, as determined by derivatographic analysis [70]. The starch content in the starch-gpoly(methyl acrylate) copolymer was determined by both side-chain separation
and thermogravimetric analysis (TGA) methods [120]. The TGA method gave
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somewhat smaller values than the side-chain separation method. However, the
TGA method was a faster and more convenient method for determining the
level of starch in graft copolymer than side-chain separation.
Using the TGA method, Tian and Wei [126] reported that the thermal stability of the starch-g-polyacrylonitrile copolymer is higher compared with the ungrafted starches. Sandle, Singh, and Verma [80] studied the graft polymerization
of 2-hydroxyethyl methacrylate (HEMA) and ethylene dimethacrylate onto
starch. The thermal behavior of the graft copolymer with different percentages
of graft add-on of HEMA (from 19.7% to 95.7%) resulted in an increase in
thermal stability; however, at higher percentages (i.e., 163.4%), a reduction in
thermal stability was observed. An improvement in thermal stability of starch
was observed on grafting with ACN [120]. An increase in grafting level resulted
in an increase in anaerobic char yield at 550°C. A graft copolymer sample having 97.7% grafting had a char yield of 52%, which was higher than that for
poly(ACN). The TGA and DSC of starch-g-poly(AM) copolymer indicated that
grafting lowers the initial decomposition temperature of starch [129]. An increase in percentage of graft add-on in the copolymer led to an overall improvement in the thermal stability.
The TGA of starch-g-poly(N-methylol acrylamide) and starch showed their
similarity in thermal stability, probably due to low grafting percentage [14]. For
alkyl methacrylates [26] (for which alkyl = methyl, ethyl, and butyl), the thermal
stability of the graft copolymers decreased. However, in general, the starch graft
copolymers showed a thermal stability between 200°C and 250°C.
The glass transition temperature Tg of starch graft copolymers is invariably
found near that of starch, not withstanding the Tg of the grafted polymer [14,
26]. Table 3 gives the Tg’s obtained by DSC for various graft copolymers.
2.9. Applications
2.9.1. Flocculant
Efficient flocculants with shear and biodegradable resistant properties were
synthesized by grafting polyacrylamide on a starch backbone [130]. The settling
rates and filtration rates following flocculation of iron ore were measured as a
function of time. It was found that the graft copolymer was as effective as a
commercially obtained flocculant, Magnafloc-1011.
Chan and Chiang [131] demonstrated the use of water-soluble and waterinsoluble starch grafted with AM and sodium sulfonate as flocculants in the
flocculation of clay suspension. Studies were also conducted on the synthesis
of starch-g-poly(acrylamide-co-sodium allylsulfonate) and its application to the
flocculation of kaolin suspension [119]. Cationic starch-g-polyacrylamide copolymer showed good flocculation ability which can be used in the paper indus-
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TABLE 3
Glass Transition Temperature of Starch and
Various Starch Graft Copolymersa
Polymer
Glass transition
temperature, °C
Starch
Starch-g-poly(methyl methacrylate)
Sarch-g-poly(ethyl methacrylate)
Starch-g-poly(butyl methacrylate)
Starch-g-poly(acrylonitrile)
Starch-g-poly(methacrylonitrile)
Starch-g-poly(N-methylol acrylamide)
Starch-g-poly(methacrylic acid)
80.7
72.8
77.4
78.9
83.3
87.1
75.0
74.8
a
Determined by differential scanning calorimetry.
try to increase the retention of filter, water drainage rate of slurry, and paper
strength [69].
Starch-g-poly(acrylic acid), starch-g-poly(acrylamide-co-acrylic acid), and
starch-g-poly(acrylamide-co-[β-(methacryloyloxy)ethyl]trimethylammonium
ethyl sulfate) copolymers were used as flocculants for bauxite ore red mud suspensions [132]. Flocculation of 5% kaolinite suspensions was accelerated by the
addition of starch-g-poly(AM) copolymer [133]. The sedimentation rate, residual turbidity, and filtration rate were increased with the increase in the concentration of the copolymer in suspension. The sedimentation rate of the suspension
containing 0.1% copolymer (based on kaolinite) was 12-35 cm/min compared
with 1 cm/min for the suspension without the copolymer.
Acrylamide and N-methylol acrylamide were grafted onto starch, and their
flocculating ability was tested for kaolin suspensions [134]. Starch-g-polyacrylamide showed about the same flocculation action as the common polymer flocculants. The use of starch-g-poly(acrylamide-co-acrylic acid) as a flocculant for
kaolin has also been reported [135]. Gu [136] has reported the use of cationic
starch-graft-polyacrylamide copolymer as a flocculant in the treatment of paper
mill white water. The results showed that the graft copolymer treatment of white
water resulted in a higher solid recovery rate, shorter flocculation time, and
smaller amount compared to the anionic polyacrylamide. The synthesis, characterization, and testing of starch-graft-polyacrylamide has been reported by Singh
[137]. He observed that the flocculant prepared from the graft copolymer was
shear, as well as biodegradation, resistant and showed a good drag reduction.
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2.9.2. Ion-Exchange and Chelating Resins
The efficiency of starch-g-poly(AA) for removing Hg2+, Cd2+, Pb2+, Cu2+, and
Cr from wastewater was studied, and the removal mechanism and influencing
factors have been discussed [137]. Starch-g-poly(ACN), treated with sodium
hydroxide, was found to be effective for the removal of Zn2+ and Cd2+ from
waste water [139]. Cation-exchange resins containing phosphoric acid groups
were prepared by grafting glycidyl methacrylate onto starch [60].
The evaluation of the alkali-treated starch-g-polyacrylamide copolymer as a
cation exchanger has been carried out [140]. The absorption efficiency of different cations was found to be dependent on the associated anions and follows the
order Cu2+ > Zn2+ > Co2+ > Mg2+. Different types of cationic starches were prepared via reacting methylolated starch-g-poly(AM) copolymer with different
aminating agents [141]. Heavy metal anion removal efficiency depends on the
cationic starch used, as well as the removed anion. The removal efficiency of
anions and the sorption efficiency of all the metal ions of different cationic
starches followed the order NH3 derivative > triethylamine derivative > ethylamine derivative > ethylenediamine derivative > diethylamine derivative. The
metal ion sorption behavior of the cationic starches followed the order Pb2+
> Cd2+ > Zn2+ > Cu2+ > Co2+. The cationic starch bearing primary amino groups
showed the highest metal ion sorption efficiency, irrespective of the sorbed
metal ion.
Starch was grafted with N-acryloyl-N′-cyanoacetohydrazide to produce gels
that showed a great tendency toward complexation with many cations [142].
Chelation with CuCl2, NiCl2 and CrCl3 solutions were spectrophotometrically
investigated. Stability constants of the formed complexes were of the order of
10 7. The use of starch-g-poly(glycidyl methacrylate-co-acrylic acid) as a cation
exchange composite has also been reported. Acrylic acid, methacrylic acid, or
ethyl acrylate were grafted polymerized onto starch and neutralized with sodium
hydroxide to give polymers that were useful dispersants, having both chelating
ability for heavy metal ions and biodegradability by enzyme [143].
Okieimen, Nikumah, and Egharevba [144] studied the grafting of AA onto
starch and reported that the attachment of the grafts to starch led to marked
improvement in water retention capacity and metal ion binding capacity of the
polymeric substrate. The equilibrium sorption data for Cu(II) on starch graft
copolymers fitted the Freundlich isotherm, with the coefficient and exponent of
isotherm being 0.40 and 0.60, respectively. The distribution coefficient for
Cu(II) between the polymeric substrate and the bulk aqueous phase depended
on the concentration of the metal ion solution, indicating that Cu(II) ions were
adsorbed strongly on the starch graft copolymers. Starch-g-poly(AM) copolymer
was found to be useful as a flocculant for treating wastewater containing Hg2+
from the paper industry [145].
3+
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2.9.3. Superabsorbents
Starch-g-poly(AA) sodium salt copolymer has been used as an absorbent in
the treatment of radioactive wastewater coming from power equipment [146].
The water absorbents do not generate toxic substances even on firing to solidify
them. Starch-g-poly(AA) sodium salt has also been used as gelling agent in
alkaline zinc batteries [147]. A Japanese patent [148] describes the use of starchg-poly(AA) sodium salt copolymer in the manufacture of three-layer wound
dressings. The wound dressings act as a barrier for microorganisms and prevent
the adhesive from leaking. Starch graft copolymers prepared from AA and 3chloro-2-hydroxypropyl acrylate were found to be good water absorbents for
use in diapers and as cosmetic thickeners [149].
A European patent [150] describes the use of starch-graft-poly(acrylic acid)
sodium salt in a controlled-release transdermal therapeutic system as a waterabsorbing resin. A water-absorbing resin prepared from starch-graft-poly(AA)
sodium salt was used to control road dust [151]. When the copolymer gel was
sprayed on a dusty road, it was observed to retain sufficient water for effective
control for 15–20 days.
Starch-graft-poly(AM) has been applied as an environmentally friendly agent
for the following purposes: (1) as a formaldehyde scavenger from formaldehyde
resins, especially urea-formaldehyde resins used in chipboards and (2) as an
agent for reducing drag flow in pipelines for waste liquids. The proposed
method of the production of the formaldehyde scavenging agent was reported
to be wastefree. The copolymer is a harmless and nontoxic product useful for
environmental protection [152].
2.9.4. Sizing Agents and Thickeners
Sizes for spun yarns with good storage stability and good miscibility were
prepared from starch-g-poly(AA) [153]. Hebish, El-Alfy, and Bayazeed [154]
graft polymerized AM, AA, methyacrylic acid, and ACN independently onto
starch to synthesize vinyl polymer–starch composites for serving as size base
materials.
Gugliemelli, Weaver, and Russell [155] reported that the dispersions of
starch-g-poly(ACN) copolymer in brine had high viscosity and limited sensitivity to high salt concentrations, which made them useful as bodying agents for
use in secondary marine recovery operations.
Jones and Elmquist [156] found that starch-g-poly(AM-co-AA) copolymer
was very effective as printing paste thickener if used together with commercial
thickener such as sodium alginate. The graft reaction of AM on lintnerized
potato starch produced a water-soluble thickener with molecular properties of
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the product controlled, in part, by the gel effect induced in all the syntheses
[157].
Application of starch-graft-poly(methacrylic acid) treated with either polyethylene glycol or silicate compound as the surface size resulted in significant
improvement of surface properties of paper, such as gloss, oil absorbency,
smoothness, porosity, and printability [158]. Mostafa and El-Sanabary [159] has
reported that the physicomechanical properties of cotton textiles, such as tensile
strength, elongation at break, and abrasion resistance, were highly enhanced
when starch-graft-polyacrylamide copolymers were used as the size base materials, while the poorest textile properties were observed when the original starch
was used as a sizing agent.
2.9.5. Other Uses
The use of starch-graft-poly(methacrylic acid) in cotton fabric finishing
showed an increase in tensile strength, elongation at break, and abrasion resistance, but the dry wrinkle recovery angle decreased [160, 161].
Starch graft copolymers prepared from AM, AA, and dimethylaminoethyl
methacrylate, when used as additive in papermaking, showed an enhancement
in the bursting strength [162, 163].
3. CONCLUDING REMARKS
In this paper, a systematic attempt has been made to present the subject
matter of graft polymerization using starch as the model substrate. The different
methods used for initiating the graft polymerization of vinyl monomers have
been discussed at length. In the present article, although starch has been used
as the substrate, either one or all of the initiation techniques (depending on the
nature of substrate) can be used for the graft polymerization of vinyl monomers
onto other polymers. Thus, using the graft polymerization technique, tailor-made
polymers suitable for particular end-use requirements can be synthesized.
LIST OF ACRONYMS
AA
ACN
AGU
BMA
CAN
EMA
MA
MMA
acrylic acid
acrylonitrile
anhydroglucose unit
butyl methacrylate
ceric ammonium nitrate
ethyl methacrylate
methyl acrylate
methyl methacrylate
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REFERENCES
1. J. Brandrup, in Polymer Handbook, 3rd ed. (J. Brandrup and E. H. Immergut,
Eds.), John Wiley and Sons, New York, 1989, pp. 1–36.
2. G. F. Fanta and W. M. Doane, in Modified Starches: Properties and Uses (O. B.
Wurzburg, Ed.), CRC Press, Boca Raton, FL, 1987, p. 149.
3. R. Chinnaswamy and M. Hanna, Starch/Staerke, 43(10), 396 (1991).
4. F. L. Bucholz, Trends Polym. Sci. (Cambridge, U.K), 2(8), 277 (1994); Chem.
Abstr., 122, R135045 (1994).
5. Y, Zhang and G. Li, Tianran Chanwu Yanjiu Yu Kaifa, 2(4), 65 (1990); Chem.
Abstr., 115, R160349s (1991).
6. F. Masuda, CEER, Chem. Econ. Eng. Rev., 15(11), 19 (1983); Chem. Abstr., 100,
R86787e (1984).
7. K. Nukashina, Yuki Gosei Kagaku Kyokaishi, 38(6), 546 (1980); Chem. Abstr.,
94, R66783e (1981).
8. J. Schurz, Int. Congr. Pure Appl. Chem. [Proc], 27, 307 (1980); Chem. Abstr., 93,
R150671d (1980).
9. F. Masuda, Sanyo Kasei Nyusu, 278, 1 (1980); Chem. Abstr., 92, R216343m
(1980).
10. H. Kubota, Kagaku Kogyo, 30(9), 928 (1979); Chem. Abstr., 91, R194232z
(1979).
11. H. G. Elias, Polym. News, 4(1), 26 (1977); Chem. Abstr., 88, R23918m (1978).
12. I. Sakurada, Kobunshi Kako, 25(7), 208 (1976); Chem. Abstr., 85, R179346x
(1976).
13. G. F. Fanta, in Block Graft Copolymers (R. J. Ceresa, Ed.), Wiley, London, 1973,
chap. 1, p. 29.
14. V. D. Athawale and S. C. Rathi, J. Polym. Mater., 13, 335 (1996).
15. M. Vera-Pacheco, H. Vazquez-Torres, and G. Canche-Escamilla, J. Appl. Polym.
Sci., 47, 53 (1993).
16. D. R. Patil and G. F. Fanta, J. Appl. Polym. Sci., 47, 1765 (1993).
17. G. Mino and S. Kaizerman, J. Polym. Sci., 31(122), 212 (1958).
18. F. R. Duke and A. A. Froist, J. Am. Chem. Soc., 71, 2790 (1949).
19. F. R. Duke and R. F. Bromer, J. Am. Chem. Soc., 73, 5179 (1951).
20. G. F. Fanta, R. C. Burr, C. R. Richard, and C. E. Rist, J. Polym. Sci., Part A-1,
7(7), 1675 (1969).
21. G. F. Fanta, R. C. Burr, and W. M. Doane, J. Polym. Sci., Poly. Chem. Ed., 21(7),
2095 (1983).
22. L. A. Gugliemelli, C. L. Swanson, W. M. Doane, and C. R. Russell, J. Polym.
Sci., Polym. Lett. Ed., 15(12), 739 (1977).
23. B. Vazquez, I. Goni, M. Gurruchaga, J. Areizaga, M. Valero, and G. M. Guzman,
Makromol. Chem., 193(9), 2189 (1992).
24. M. Liu, S. Zhang, and J. Wu, Lanzhou Daxue Xuebao, Ziran Kexueban, 28(12),
112 (1992); Chem. Abstr., 119, 250661z (1993).
25. G. Wu and Y. Huang, Jilin Daxue Ziran Kexue Xuebao, 4, 79 (1986); Chem.
Abstr., 106, 102792j (1987).
26. V. D. Athawale and S. C. Rathi, Eur. Polym. J., 33(7), 1067 (1996).
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
ORDER
476
REPRINTS
ATHAWALE AND RATHI
27. V. D. Athawale, S. C. Rathi, and V. Lele, Eur. Polym. J., 34(2), 159 (1998).
28. G. Wu, C. Jia, D. Lu, X. Yu, and Y. Sun, Jilin Daxue Ziran Kexu Xuebao, 3, 93
(1988); Chem. Abstr., 110, 155257c (1989).
29. M. Liu, J. Wu, and G. Yue, Lanzhou Daxue Xuebao, Ziran Kexueban, 29(4), 132
(1993); Chem. Abstr., 122, 266204a (1995).
30. H. Lia and L. Huang, Guangzhou Huagong, 24(2), 30 (1996).
31. V. D. Athawale and S. C. Rathi, React. Funct. Polym., 34, 11 (1997).
32. A. Hebeish, A. Bayazeed, E. El-Alfy, and M. I. Khalil, Starch/Staerke, 40(6), 223
(1988).
33. G. F. Fanta, C. L. Swanson, R. C. Burr, and W. M. Doane, J. Appl. Polym. Sci.,
28(7), 2455 (1983).
34. M. H. Abo-Shosha and N. A. Ibrahim, Starch/Staerke, 44(8), 296 (1992).
35. B. Cao and R. Song, Huaxue Shijie, 33(1), 19 (1992); Chem. Abstr., 115, 132035j
(1992).
36. G. Wu and S. Sun, Shiyou Huagong, 20(4), 242 (1991); Chem. Abstr., 115,
257313p (1991).
37. G. Wu and L. Zhou, Shiyou Huagong, 22(5), 287 (1993); Chem. Abstr., 121,
256894r (1994).
38. X. Wang, J. Qi, and H. Xue, Gaofenzi Cailiao Kexue Yu Gongcheng, 13(1), 135
(1997); Chem. Abstr., 126, 144851w (1997).
39. G. Wu, F. Yang, and G. Zhang, Jilin Daxue Ziran Kexue Xuebao, 2, 101 (1989);
Chem. Abstr., 112, 139964s (1990).
40. C. E. Brockway and K. B. Moser, J. Polym. Sci. Part A., 1, 1025 (1963).
41. G. F. Fanta, R. C. Burr, W. M. Doane, and R. C. Russell, J. Appl. Polym. Sci.,
16(11), 2835 (1972).
42. C. E. Brockway, J. Polym. Sci., Part A: Polym. Chem., 3721 (1964).
43. B. Vazquez, I. Goni, M. Gurruchaga, M. Valero, and G. M. Guzman, J. Polym.
Sci., Part A: Polym. Chem., 27(2), 595 (1989).
44. M. I. Khalil, K. M. Mostafa, and A. Hebeish, Starch/Staerke, 42, 107 (1990).
45. R. Mehrotra and B. Ranby, J. Appl. Polym. Sci., 21(6), 1647 (1977).
46. K. Tan, K. J. Wang, A. Liu, X. Xu, and Z. Zhang, Yingyong Huaxue, 6(1), 9
(1989); Chem. Abstr., 111, 7960g (1989).
47. A. Hebeish, I. H. El-Thalouth, M. A. El-Kashouti, and S. H. Abdel-Fattah, Angew.
Makromol. Chem., 78, 101 (1979).
48. K. M. Mostafa, J. Appl. Polym. Sci., 56(2), 263 (1995).
49. C. Zhang, L. Bao, and Z. Tong, Gaofenzi Cailiao Kexue Yu Gongcheng, 10(1),
33 (1994); Chem. Abstr., 112, 11235u (1995).
50. C. Rodehed and B. Ranby, J. Appl. Polym. Sci., 32(1), 3323 (1986).
51. G. Fanta, R. C. Burr, and W. M. Doane, J. Appl. Polym. Sci., 24(9). 2015 (1979).
52. Z. Reyes, M. G. Syz, L. M. Huggins, and C. R. Russell, J. Polym. Sci., Part C.,
23(1), 401 (1966).
53. A. M. Henderson and A. Rudin, J. Appl. Polym. Sci., 27(11), 4115 (1982).
54. E. Cohen and A. Zilkha, Isr. J. Chem., 11(1), 45 (1973); Chem. Abstr., 80, 27520h
(1974).
55. M. Tahan and A. Zilkha, Eur. Polym. J., 5(2), 347 (1969).
56. J. Yu, R. Tian, and X. Liu, Tianjin Daxue Xuebao, 6, 71 (1993); Chem. Abstr.,
122, 107213m (1995).
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
ORDER
STARCH AS A MODEL SUBSTRATE
REPRINTS
477
57. R. Tian and X. Liu, Gaofenzi Xuebao, 1, 103 (1992); Chem. Abstr., 120, 108439k
(1994).
58. P. Ghosh and S. K. Paul, Indian J. Technol., 24(3), 111 (1986).
59. P. Ghosh and S. K. Paul, J. Macromol. Sci., Chem., A20(2), 261 (1983).
60. M. I. Khalil, A. Wally, S. I. Farag, and A. Hebeish, J. Appl. Polym. Sci., 43(12),
2303 (1991).
61. A. Bayazeed, S. Farag, and A. Hebeish, Starch/Staerke, 38(8), 268 (1986).
62. G. Wu, D. Lu, Y. Hu, and Y. Sun, Jilin Daxue Ziran Kexue Xuebao, 1, 86 (1989);
Chem. Abstr., 111, 78762e (1989).
63. B. Ranby, Modif. Cellul. (Symp. Cellul., Pap. Text. Div. Am. Chem. Soc.) (R. M.
Rowell and R. A. Youngs, Eds), Academic, New York, 1977, p. 171.
64. B. N. Misra, R. Dogra, I. Kaur, and D. Sood, Indian J. Chem., Sec. A., 17A(4),
390 (1979).
65. P. Ghosh and S. K. Paul, J. Macromol. Sci., Chem., A20(2), 179 (1983).
66. M. H. El-Rafie, M. K. Zahran, F. K. El-Tahlaury, and A. Hebeish, Polym. Degrad.
Stab., 47(1), 75 (1995); Chem. Abstr., 122, 188948c (1995).
67. R. L. Whistler and J. L. Goatley, J. Polym. Sci., 62(174), 123 (1962).
68. F. Wolf, H. J. Mallon, and H. Gerlach, Starch/Staerke, 32(7), 229 (1980).
69. B. Feng and S. Wu, Hebei Gongxueyuan Xuebao, 18(4), 75 (1989); Chem. Abstr.,
115, 9993b (1991).
70. Z. K. Brzozowski and K. Noniewicz, Polimery (Warsaw), 39(2), 82 (1994); Chem.
Abstr., 122, 242655x (1995).
71. Y. Wang, W. Yang, and D. Cui, Gaofenzi Xuebao, 1, 111 (1996); Chem. Abstr.,
124, 261945z (1996).
72. D. Trimnell, G. F. Fanta, and J. H. Salch, J. Appl. Polym. Sci., 60(3), 285 (1996).
73. G. Yang, W. Guo, Q. Li, S. Lu, X. Cui, S. Mo, and Y. Shi, Chin. Chem. Lett.,
2(12), 913 (1991); Chem. Abstr., 116, 256099y (1992).
74. J. Gao, R. Tian, and L. Zhang, Chin. J. Polym. Sci., 14(2), 163 (1996); Chem.
Abstr., 125, 115943b (1996).
75. A. Nagaty, A. E. Mouti, and O. Y. Mansour, Eur. Polym. J., 16(4), 343 (1980).
76. F. E. Okieimen and F. Egharevba, Makromol. Chem., Rapid Commun., 10(11),
579 (1989).
77. M. I. Khalil, K. M. Mostafa, and A. Hebeish, Agnew. Makromol. Chem., 213, 43
(1993); Chem. Abstr., 120, 77857p (1994).
78. L. A. Gugliemelli, C. L. Swanson, and W. M. Doane, J. Polym. Sci., Polym.
Chem. Ed., 11(10), 2451 (1973).
79. Y. Nakamura, T. Ouchi, and M. Imoto, Kobunshi Ronbunshu, 31(11), 678 (1974);
Chem. Abstr., 82, 86676c (1975).
80. N. K. Sandle, O. P. Singh, and I. K. Verma, Angew. Makromol. Chem., 154, 87
(1987).
81. S. H. O. Egboh and B. Jinadu, Angew. Makromol. Chem., 163, 93 (1988).
82. L. Mingzhu, C. Rongshi, W. Jingjia, and M. Cheng, J. Polym. Sci., Part A: Polym.
Chem., 31(13), 3181 (1993).
83. S. Pan, G. Li, Z. Wang, and Z. Wang, Shiyuo Huagong, 22(3), 177 (1993); Chem.
Abstr., 121, 58169v (1994).
84. T. Ruchan and W. Yuchun, Gaofenzi Xuebao, 2, 129 (1990); Chem. Abstr., 114,
102886h (1991).
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
ORDER
478
REPRINTS
ATHAWALE AND RATHI
85. J. Yu, R. Tian, and X. Liu, Tianjin Daxue Xuebao, 5, 35 (1993); Chem. Abstr.,
122, 107219t (1995).
86. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Polym. Sci., Part B,
4(10), 765 (1966).
87. C. E. Brockway and P. A. Seaberg, J. Polym. Sci., Part A-1, 5(6), 1313 (1967).
88. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Appl. Polym. Sci., 11(3)
457 (1967).
89. M. Tahan and A. Zilkha, J. Polym. Sci., Part A-1, 7(7), 1839 (1969).
90. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Appl. Polym. Sci., 11(10),
2451 (1973).
91. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Macromol. Sci., Chem.,
1(7), 1381 (1968).
92. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Macromol. Sci., Chem.,
4(2), 331 (1970).
93. R. Mehrotra and B. Ranby, J. Appl. Polym. Sci., 22(10), 3003 (1978),
94. R. Mehrotra and B. Ranby, J. Appl. Polym. Sci., 22(10), 2991 (1978).
95. N. W. Taylor, G. F. Fanta, W. M. Doane, and C. R. Russell, J. Appl. Polym. Sci.,
22(5), 1343 (1978).
96. G. F. Fanta, R. C. Burr, C. R. Russell, and C. E. Rist, J. Macromol. Sci., Chem.,
2(1) 93 (1968).
97. E. I. Stout, D. Trimnell, W. M. Doane, and C. R. Russell, J. Appl. Polym. Sci.,
21(9), 2565 (1977).
98. R. Mehrotra and B. Ranby, J. Appl. Polym. Sci., 21(12), 3407 (1977).
99. S. Takagi, T. Weda, T. Nakajima, N. Hishiki, and N. Ogura, Jpn. Pat. 63,193,910
(1988); Chem. Abstr., 110, 193657r (1989).
100. D. Castle, A. Richard, and R. J. Audebert, J. Appl. Polym. Sci., 39(1), 11 (1990).
101. R. Tian, C. Lin, J. Yu, and M. Duan, Tianran Chanwu Yanjiu Yu Kaifa, 2(2), 1
(1990); Chem. Abstr., 115, 160365u (1991).
102. G. Wu, D. Lu, Y. Sun, and G. Zhang, Jilin Daxue Ziran Kexue Xueabo, 1, 122
(1988); Chem. Abstr., 109, 23498b (1988).
103. M. Yamagachi, H. Watamoto, and M. Sakamota, Carbohydr. Polym., 7(1), 7
(1987).
104. C. Rodehed and B. Ranby, Polymer, 27(2), 313 (1986).
105. R. C. Burr, G. F. Fanta, and W. M. Doane, J. Appl. Polym. Sci., 24(5), 1387
(1979).
106. G. Ma, S. Du, and C. Luo, Chin. Pat. 1,058,972 (1992); Chem. Abstr., 118,
103593e (1993).
107. M. Jin and Q. Yin, Shuichuli Jishu, 13(4), 208 (1987); Chem. Abstr., 108,
151423q (1988).
108. D. Huang, Y. Xue, H. Qiu, M. Huang, S. Lu, and Jiang, Gaofenzi Cailiao Kexue
Yu Gongcheng, 7(1), 105 (1991); Chem. Abstr., 116, 10791m (1992).
109. V. D. Athawale and S. C. Rathi, J. Appl. Polym. Sci., 66, 1399 (1997).
110. L. C. Swanson, G. F. Fanta, R. G. Fecht, and R. C. Burr, Polym. Sci. Technol.
(Polym. Appl. Renewable-Resource Mater.), 17, 59 (1983).
111. D. L. Lim and S. S. Im, Pollimo, 18(3), 368 (1994); Chem. Abstr., 121, 135788a
(1994).
112. G. F. Fanta, D. Trimnell, and J. Salch, J. Appl. Polym. Sci., 49(9), 1679 (1993).
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
ORDER
STARCH AS A MODEL SUBSTRATE
REPRINTS
479
113. T. Nakajima, S. Takagi, and T. Ueda, Jpn. Pat. 04,202,567 (1992); Chem. Abstr.,
118, 40174w (1993).
114. D. R. Patil and G. F. Fanta, Starch/Staerke, 46(4), 142 (1994).
115. G. F. Fanta and O. H. Otey, U.S. Pat. 123,411 (1988); Chem. Abstr., 110:9365v
(1989).
116. G. F. Fanta, D. Trimnell, and J. H. Salch, Polym. Prepr., 34(2), 594 (1994).
117. B. Vazquez, I. Goni, M. Gurruchaga, M. Valero, and G. M. Guzman, J. Polym.
Sci., Part A: Polym. Chem., 30(8), 1541 (1992).
118. K. J. Yao and Y. B. Tang, J. Appl. Polym. Sci., 45(2), 349 (1992).
119. J. Gao, R. Tian, J. Yu, and M. Duan, J. Appl. Polym. Sci., 53(8), 1091 (1994).
120. N. K. Sandle, O. P. Singh, and I. K. Verma, Angew. Makromol. Chem., 121, 187
(1984).
121. X. Jian, X. Zeng, and W. He, Guangxi Shifan Daxue Xuebao, Ziran Kexueban,
11(1), 47 (1993); Chem. Abstr., 122, 57261c (1995).
122. I. Goni, M. Gurruchaga, M. Valero, and G. M. Guzman, Polymer, 33(14), 3089
(1992).
123. M. Gurruchaga, I. Goni, B. Vazquez, M. Valero, and G. M. Guzman, Makromolecules, 25(12), 3009 (1992).
124. B. Vazquez, M. Gurruchuga, I. Goni, M. Valero, G. M. Guzman, and San Roman,
J. Macromol., 26(16), 4298 (1993).
125. S. Ganapathy, P. R. Rajamohan, S. S. Ray, A. B. Mandhare, and R. A. Mashelkar,
Macromolecules, 25(12), 3009 (1992).
126. R. Tian and Y. Wei, Yingyong Huaxue, 6(5), 83 (1989); Chem. Abstr., 112,
139995c (1990).
127. C. Rodehed, B. Ranby, M. D. L. Bayona, and R. Mehrotra, Starch/Staerke,
37(11), 367 (1985).
128. V. D. Athawale and V. Lele, Carbohydr. Polym., 35, 21 (1998).
129. O. P. Singh, N. K. Sandle, and I. K. Verma, Angew. Makromol. Chem., 121, 187
(1984).
130. G. P. Karmarkar, R. P. Bhagat, D. M. Chakraborty, and R. P. Singh, in Polymer.
Science, Vol. 2 (I. S. Bhardwaj, Ed.), Allied, New Delhi, India, 1994, p. 990.
131. W. Chan and C. Chiang, J. Appl. Polym. Sci., 58(10), 1721 (1995).
132. D. A. Jones and L. F. Elmquist, Starch/Staerke, 25(3), 83 (1973).
133. T. Hirano and T. Hasegawa, Kogyo Kagaku Zasshi, 74(1), 91 (1971); Chem. Abstr., 74, 142942t (1971).
134. M. Inano, Kogyo Kagaku Zasshi, 72(10), 2298 (1969); Chem. Abstr., 72, 68445r
(1970).
135. R. Zhu and D. Zhao, Huaxue Shijie, 30(11), 495 (1989); Chem. Abstr., 113,
414642z (1990).
136. Y. Gu, Guangzhou Huagong, 24(1), 59 (1996); Chem. Abstr., 125, 95342z (1996).
137. R. P. Singh, in Polym. Other Adv. Mater. (Proc. Int. Conf. Front Polym. Adv.
Mater.), 3rd ed., (P. N. Prasad, J. E. Mark, and J. F. Tung, Eds.), Plenum, New
York, 1995, p. 227.
138. Y. Wang, Q. Han, Z. Huang, and Y. Tang, Water Treat., 6(3), 339 (1991); Chem.
Abstr., 116, 112889s (1992).
139. C. Jin, D. Zhou, and H. Liu, Huaxue Shijie, 26(11), 415 (1985); Chem. Abstr.,
104, 89575c (1986).
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
ORDER
REPRINTS
480
ATHAWALE AND RATHI
140.
141.
142.
143.
M. I. Khalil, S. Farag, and A. S. El-Fataeh, J. Appl. Polym. Sci., 57(3), 335 (1995).
M. I. Khalil and S. Farag, Starch/Staerke, 46(1), 17 (1994).
M. G. Mikhael and W. M. Kulichke, Starch/Staerke, 44(7), 264 (1992).
I. Park, T. S. Park, and Y. Kim, PCT Int. 93 02,118 (1993); Chem. Abstr., 119,
96966u (1993).
F. E. Okieimen, J. E. Nikumah, and F. Egharevba, Eur. Polym. J., 25(4), 423
(1989).
G. Wu, Y. Sun, Q. Li, and G. Zhang, Jilin Daxue Ziran Kexue Ziran, 123 (1989);
Chem. Abstr., 110, 154973w (1989).
T. Seto, R. Yoshikawa, and A. Komatau, Jpn. Pat. 06,238,261 (1994); Chem.
Abstr., 121, 310161q (1994).
K. Tada, M. Kurimura, and M. Yano, Jpn. Pat. 04,286,865 (1992); Chem. Abstr.,
118, 106324d (1993).
K. Yamamoto, T. Watanabe, and T. Yamamoto, Jpn. Pat. 06 00,201 (1994);
Chem. Abstr., 120, 173553g (1994).
W. G. Chiang, Can. Pat. 2,097,885 (1993); Chem. Abstr., 121, 257417z (1994).
M. Mori, Eur. Pat. 739,626 (1995); Chem. Abstr., 125, 309098a (1996).
H. Wang, Shanghai Huanjing Kexue, 15(4), 21 (1996); Chem. Abstr., 126,
228797w (1997).
Z. K. Brozozowski, Zywn., Technol., Jakosc., 2, 110 (1996); Chem. Abstr., 126,
20347s (1997).
T. Katayama, H. Myazaki, N. Hishiki, T. Nakajima, and Y. Watenabe, Jpn. Pat.
06 73,666 (1994); Chem. Abstr., 121, 159336c (1994).
A. Hebeish, E. El-Alfy, and A. Bayazeed, Starch/Staerke, 40(5), 191 (1988).
L. A. Gugliemelli, M. O. Weaver, and C. R. Russell, U.S. Pat. 3,425,971 (1969);
Chem. Abstr., 70, 69444k (1969).
D. A. Jones and L. F. Elmquist, Starch/Staerke, 24(1), 23 (1972).
J. J. Meister and M. L. Sha, J. Appl. Polym. Sci., 33(6), 1859 (1987).
P. Aravindakshan and V. N. G. Kumar, U.S. Pat. 5,583,193 (1996); Chem. Abstr.,
126, 105662r (1997).
K. M. Mostafa, Polym. Degrad. Stab., 55(2), 125 (1997); Chem. Abstr., 126,
132843g (1997).
K. M. Mostafa, Am. Dyest. Rep., 85(9), 85 (1996); Chem. Abstr., 125, 278452e
(1996).
K. M. Mostafa and A. A. El-Sanabary, Am. Dyest. Rep., 85(5), 37 (1996); Chem.
Abstr., 125, 60848 (1996).
E. Natsuhara and N. Abu, Jpn. Pat. 08,109,594 (1996); Chem. Abstr., 125,
117866c (1996).
E. Natsuhara and N. Abu, Jpn. Pat. 08,06,591 (1996); Chem. Abstr., 125, 36173x
(1996).
144.
145.
146.
147.
148.
149.
150.
151.
152.
153.
154.
155.
156.
157.
158.
159.
160.
161.
162.
163.
Downloaded By: [Technical University of Wien] At: 09:12 20 November 2007
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