Indian Journal of Chemical Technology
Vo l. 8, November 200 I. pp. 510-514
Phase transfer catalysed polymerisation of butyl methacrylate using potassium
peroxydisulphate as initiator-A kinetic study
M J Umapathy & D Mohan
De partment of Chemical Engineering, AC College of Technology, Anna University, Chennai 600 O.:c5, India
Received 3 February 2000; revised 23 May 2001; accepted 28 Jun e 2001
The kineti cs of phase transfer catalysed free radical polymerisation of butyl methacrylate using potassium peroxydisulphate as water soluble initiato r and propiophenonebenzyldimethylammonium chlo ride (PPBDAC) as phase transfer catalyst
were studi ed. The po lymeri sa tion reactions were carried out in cyclohexanone-water biphase media at 60°C in an inert atmos phere und er un stirred conditio n. The effect of various experimental co nditions such as different concentrations o f
mo no mer, initiato r, phase tran sfer catalyst (PTC) and different ionic strength , temperature and the volume frac tion of aqueo us phase is studi ed. The order wi th respect to monomer, initiator and the phase transfer catalyst is found to be I, 0.5 and 0.5
respecti vely. The rate of polymeri sati o n (Rp) is independent of ionic strength and pH. However, an increase in the polarity of
so lvent and vo lume fraction of aqueous phase slightly increases the RP value. Based on the results obtained, a mechani sm
has bee n proposed for the po ly meri sati o n reaction.
Phase transfer catalysed polymerisation has been an
interesting area of research in recent years since high
molecular weight polymers with high yield under
mild reaction condition can be obtained compared to
conventional free radical polymerisation method.
Polymers prepared by this technique include polycar1
2
3
bonates , polysulphonates , polyphosphonates , poly5
esters4, polyethers etc. Generally in nucleophilic substitution reactions , the substrate which is soluble in
organic solvent and the reactant soluble in water may
not mix thoroughly for the reaction to complete. A
catalyst capable of carrying the reactant from the
aqueous phase to the organic phase in order to make it
available completely for the substrate to react is the
principle of phase transfer catalysis. Many attempts
have been made on phase transfer catalysed free radical polymerisation. The first report on phase transfer
catalysed free radical polymerisation was by Rasmussen and Smith 6 . They reported the polymerisation of
butyl acrylate using various crown ethers in acetone
as phase transfer catalysts and potassium peroxydisulph ate as water soluble initiator. Jayakrishnan and
Shah7·8 investigated the polymeri sation of acrylonitrile
and methyl methacrylate usin g hex adecylpyridirium
chloride in ethyl acetate-water medium. Mandai and
Gosh9 reported the free radical pol y merisation of styre ne and methyl methacrylate using potassium peroxydi sulphate as the initiator and tetrabutylammonium bromide as phase transfer catalysts. Choi and
Lee 10 studied the kinetics of bulk (free radical)
polymerisation of methyl methacrylate with potassium peroxydisulphate-18-crown-6 catalyst system.
In this work the kinetics of the free radical polymerisation of butyl methacrylate using PPBDMAC as
phase transfer catalyst and potassi um peroxydisulphate as the water soluble initiator in cyclohexanonewater biphase medium has been studied. Based on the
results obtained under varying experimental parameters a mechanism has been proposed.
Experimental Procedure
The monomer butyl methacrylate (LR CDH), cyclohexanone (LR BDH), methanol (LR BDH), potassium peroxydisulphate (LR BDH) were purified by
standard procedure. The phase tran sfer catalyst viz. ,
propiophenonebenzyldimethyl-amrnonium chloride''
was synthesised and used for this study. Polymerisation was carried out in the presence of nitrogen
atmosphere at 60°C under unstirred condition in a
long pyrex glass polymerisation tube (4 x 20 em) of
80 mL capacity with B-24 sockets B-24 concentrations with a provision for inlet and outlet of nitrogen
gas. The reaction mixture comprised 10 mL of
organic phase containing monomer and solvent and
I 0 mL of aqueous phase containing potassium peroxydisulphate, phase transfer catal ys t, sulphuric acid
and potassium bisulphate. Sulphuric acid and potassium bisulphate were used to maintain acid and ionic
strength respectively . Polymerisation started on adding the initiator and precipitate formed continuously
UMAPATH Y & MOHAN: PHASE TRANSFER CATAL YSED POL YMERISATION OF BUTYL METHACRYLATE
.
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Time, min
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70
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2.6
2.0
2.1
2.4
A : 2 + lo~ lBMAl: B : I BMAI. moldm
3.0
-
3.2 - A
8
4
Fig. !-Steady state rate of Polymerisation
Fig. 2-Effect of [monomer] on Rp
during polymerisation. The reaction was arrested by
pouring the reaction mixture into ice-cold methanol
containing traces of hydroquinone. The rate of
12
polymerisation (Rp) was determined by gravimetry
and the conversion was restricted to within 15 percent. Viscosity measurements of the fractionated
polymer were carried out in butanone at 30°C using
Ubbelohde suspended level viscometer equipped with
a large reservoir permitting dilutions to be made in the
viscometer itself. Intrinsic viscosities were evaluated
from the linear plots of ll sp/c versus C. Average degree
sus log [BMA] and the value was found to be unity . A
plot of RP versus [BMA]' -0 is linear passing through
the origin (Fig. 2).
of polymerisation (l;,) were calculated from the intrinsic viscosity data by making use of the Mark.
. k'1· equatiOn.
Houwm
Results and Discussion
The steady state rate of polymerisation was first arrived by determining Rp at different time intervals and
it was found to be 50 min. The reaction time was
fixed at 50 min to carry out the experiments with
variation in other parameters (Fig. 1).
Effect of monomer concentration on rate of polymerisation (Rp)
The effect of monomer concentration on Rp was
studied by varying [BMA] in the range 0.7 to 2.1 M at
fixed concentrations of initiator, catalyst, acid
strength, ionic strength and volume ratio of aqueous
to organic phase. The rate of polymerisation increases
with increasing monomer concentration and the order
of the reaction was obtained from a plot of log Rp ver-
Effect of initWtor concentration on rate of polymerisation (Rp)
The effect of initiator concentration on Rp was
studied by carrying out the reaction at varying initiator concentration in the range 0.08 to 0.18 M at fixed
concentration of monomer, catalyst, acid strength,
ionic strength and volume ratio of aqueous to organic
phase. RP was found to increase with increasing concentration of the initiator. The plot of log Rp versus
log [K2S20 8] is linear with a slope of 0.5, indicating
the half order dependence of Rp on [K 2S 20 8]. A plot
0
of Rp versus [K 2S2 0 8] ·5 is linear passing through the
origin confirming the above observation (Fig 3). The
order with respect to initiator is observed to be 0.5
wherever termination is bimolecular in the free radical
polymerisation process. It also suggests that the
monomer induced decomposition of Q2 S2 0 8 is absent
where Q2S20 8 is the complex formed between the
phase transfer catalyst (Q) and the initiator peroxydisulphate (S20s).
A similar rate of polymerisation with respect to
[K2S 20 8) has been reported for the polymerisation of
acrylo nitrile with same phase transfer catalyst initi14
ated system
and methyl acrylate with benzyltributylammonium chloride as phase transfer catalyst15.
INDIAN J. CHEM . TECHNOL., NOVEMBER 2001
512
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1.7
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-
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1.6
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lil
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at
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0 .9
0 .02
1.0
0 .04
A : 3+1oQ [ S2
1.1
0.06
1.2
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o! J; B :
I. J
4
4
2
2
-A
uo 1.12 1.14- 8
[S 2 0 1 J0 · 5 xJOZ tmol.dm - 3 ) 0 ·1
0 .9
0 .04
1.0
0 .0&
1.1
0 .08
1.2
0 .10
1.3 - A
0 .12
0.14 - B
A : J•log IPPBOMAC); B : IPPBDMACivt x 102 tmoldm->JV1
Fig. 3-Effect of [initiator] on R"
Fig. 4-Effect of [PTC] on R"
Effect of phase transfer catalyst concentration on rate
ofpolymerisation (Rp)
The effect of concentration of phase transfer catalyst viz., propiophenonebenzyldimethylammonium
chloride on the polymerisation rate was studied by
varying the concentration in the range 0.07 to 0.17 at
definite concentrations of monomer, catalyst, initiator,
acid strength, ionic strength and volume ratio of
aqueous to organic phase. Rp is found to increase with
increase in concentration of the catalyst. The order
with respect to the concentration of the catalyst is
found to be arou nd 0.5 from a plot of log Rp versus
log [PTC] . A plot of Rp versus [PTC] 05 is linear
passing through the origin confirming the above result. It has al so been observed that in the absence of
phase transfer catalyst, no polymerisation occurred
even after several hours (Fig. 4).
there is a slight increase in RP with an increase m
V-/Vo ratio.
Effect of variation of volume fraction of aqueous
phase on Rp
To study the effect of variation in the volume fraction of aqueous phase on Rp the reaction was conducted with varyi ng volumes of aqueous phase with a
constant volume of organic phase at fixed concentration of monomer. initiator, catalyst, acid strength and
io nic strength. The ratio of volumes V-/V0 was varied
in th e range 0 .5 to 1.0 and it has been observed that
Effect of solvent on rate ofpolymerisation (Rp)
The effect of solvent on Rp was examined by carry ing out the polymeri sation reaction for BMA in
three different solvents viz., cyclohexane, ethyl acetate and cyclohexanone having the dielectric constant
2.02, 6.02 and 18.3 respectively. It was found that the
Rp decreased in the following order. Cyclohexanone >
ethyl acetate > cyclohexane. The decrease in the rate
of polymerisation may be due to the increase in the
polarity of the organic medium which facil itated
greater transfer of peroxydisulphate to the organic
phase.
Effect of variation of temperature
sation (Rp)
011
rate of polymeri··
The effect of temperature on Rp was studied, and it
was found that Rp increases with temperature. From a
plot of Jog Rp versus liT, the activation energy (Ea)
was calculated (Ea = 11 .00 k.cal.mol- 1) . The other
thermodynamic parameters were also calculated. (Mf
= 10.33, k.cal.mol- 1, !JS#=-57.68, eu) and !JG#=
29.39, k.cal. mor') (Fig. 5) .
513
UMAPATHY & MOHAN: PHASE TRANSFER CAT AL YSED POL YMERISATION OF BUTYL METHACRYLATE
1.4
0 .6
.. t
0.4
><
03
~
-l•n.c:
0 .2
0.6
2.94
2
3.1 0 -
Fig. 5- Effect of temperature on Rp
Phase Transfer
K
(W)
4
~
6
7
8
Fig. 6-Dependence of degree of polymerisation {Pn) on [K2S20sl
Mechanism and rate law
2Q + +S 2 o ~ -- (Q +) 2 S 2 o~-
3
... (l)
decomposition of this ion-pair takes place in the organic phase leading to the formation of Q+so4·-.
Applying the general principles of free radical polymerisation and stationary state hypothesis to the
radical species, the rate law for this mechanism can be
derived as
(0)
... (6)
Initiation
k"
(Q + )2s 2 o ~- -~2Q + so:-
(O)
(0)
. . . (2)
k;
.
Q+so:- +M--7M 1 (M - 0-SO ~ Q + )
0
(0)
. .. (3)
Propagation
(4)
k,,
M n-1+M--~M "
(5)
Termination
.
2M "
This expression satisfactorily explains all the experimental results and observations .
Dependence of degree of polymerisation (P.J on potassium peroxydisulphate concentration
Degree of polymerisation of polymers, obtained
employing various concentrations of potassium peroxydisulphate, were calculated from the intrinsic viscosity data and are found to decrease with increase of
potassium peroxydisulphate concentrations. A plot of
11~, versus [K 2S2 0 8t' gives a straight line passing
through the origin. This observation lends strong support to the mechanism proposed (Fig. 6)
k,
---7
Polymer
.. . (6)
The subscripts (w) and (o) refers to aqueous phase
and organic phase respectiv ely. This mechanism involves the formation of quaternary ammonium peroxydisulphate complex ((Q+h S2 0 l-) in aqueous
phase which is then tran sferred to organic phase. The
Conclusion
The kinetic features such as the rate of polymerisation (Rp) of free radical polymerisation of butyl methacrylate with the increasing concentration of monomer, initiator, catalyst and aqueous volume fraction s.
The [H+] and ionic strength of the medium do not
514
INDIAN J. CHEM. TECHNOL., NOVEMBER 2001
show any appreciable effect in the Rr. The reaction
rate increases with increas ing temperature. The reaction order of the polymerisation of BMA is in accordance with general rate law of radical polymerisation
with respect to the concentration of initiator and
catalyst. The effect of variation in the volume fraction
of aq ueous phase on Rr with constant volume of organ ic phase at fixed concentrations of monomer, peroxyd isulphate, phase transfer catalyst and at constant
acid and ionic strenght was studied. It has been observed that Rr increased slightly with increase in
V./V0 • A mechanism for the polymerisation of BMA
has been proposed and it has been confirmed by the
inverse rel ationship existing between the degree of
polymerisation P" and [K2S20 st'.
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