http://www.e-polymers.org
e-Polymers 2007, no. 025
ISSN 1618-7229
Comparison Of Reaction Pathway And Product Analysis
For Hydroxyalkylation Of Parabanic Acid With Oxiranes
And Alkylene Carbonates
Iwona Zarzyka-Niemiec
Rzeszów University of Technology, Department of Organic Chemistry, Al. Powstańców Warszawy 6, 35-959 Rzeszów, Poland, [email protected]
(Received: 30 November, 2006; published: 1 March, 2007)
Abstract: Reactions of parabanic acid (PA) with ethylene and propylene oxides
and carbonates lead to oligomeric products with hydroxyalkyl groups in both cases.
The parabanic acid ring undergoes scissions during reactions depending on kind of
reagent and reaction conditions. In some cases the trioxoimidazolidine ring remains untouched. Using the MALDI ToF technique the product analysis was performed. The by-products were determined quantitatively by GC. The thermostability
of oligomeric products was also determined.
Introduction
N-(2-Hydroxyalkyl) hydroparabanates (II) and N,N’-bis(2-hydroxyalkyl) parabanates
(III) can be obtained by direct reactions between PA (I) and 1 or 2 equivalents of ethylene oxide (EO) and/or propylene oxide (PO), respectively [1,2]:
O
O
C
C
HN
C
O
(I)
NH
H2C
CH
O
TEA
O
O
R C
HN
C
N CH2 CH OH
C
R
O
(II)
O
H2C
CH
O
TEA
O
C
C
R
HO CH CH2 N
N CH2CH OH (1)
C
R
R
O
(III)
where: R = H-, CH3-.
The products have sharp melting points [1, 2]. Syntheses were conducted in DMF or
without solvent in presence of triethylamine (TEA) as catalyst (<0.03 mole TEA/mole
PA) as well as in absence of catalyst at temperature not higher than 40 °C [1, 2]. We
have found that in the reaction of PA with PO only the products of normal ring opening of oxirane are formed (III, R= CH3-) [2].
At higher temperature (above 70 °C) or in presence of larger amount of catalyst, the
opening of trioxoimidazolidine ring takes place and T-shaped oligomeric products (IV)
are formed, containing secondary amide groups:
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O O
CH CH2 O C C N CH2 CH O
R
C O R
HN CH2 CH OH
R
The mechanism of reaction was discussed in details in [3].
(IV)
As hydroxyalkylating agents the alkylene carbonates (AC) can also be used. The reactions of PA with those reagents are either accompanied by evolution of carbon dioxide or with preservation of carbonate group in products [4-8]. The former processes
occur at temperatures above 120 °C with formation of various hydroxyalkylated products, similar to those obtained by reaction of PA with oxiranes [9, 10].
When PA is subjected to hydroxyalkylation with alkylene carbonates, it behaves in
different way than other azacyclic compounds. The major difference is trioxoimidazolidine ring opening during the reaction and formation of H-shaped oligomeric products (V) [11-13].
OO
HO CH2 CH O C C N CH2 CH O H
w
x
R
H
C O
R
O CH CH2 z N CH2 CH O H
(V)
R
y
R
where: R = H-, CH3.
The N,N’-bis(hydroxyalkyl)parabanates obtained by reaction of PA with oxiranes
were used as starting diols for synthesis of polymers of enhanced heat resistance
and thermal stability. Thus the polyurethanes, polyesters [14] and polyester resins
[15] with trioxoimidazolidine ring were obtained and their properties were compared
with standard polymers. It was found that introduction of trioxoimidazolidine ring to
polyurethane resulted in higher heat resistance but not thermal stability [14]. Different
result was obtained for polymethacrylates and acrylates, for which both heat resistance and thermal stability enhancement, was found [14].
Here we compare the structure and properties of the products of reaction between
PA and oxiranes with these obtained form PA and AC. The influence of condition of
the synthetic process on the trioxoimidazolidine ring percentage in the product and
the percentage of by-products is described. The use of MALDI ToF technique enabled identification of univocally the products of reaction between PA and oxiranes or
alkylene carbonates. The thermal stability studies on the products of reaction between PA with oxiranes are here described in detail for the first time.
Results and discussion
According to our previous studies the determination of acidic number of products of
reaction between PA and oxiranes by titration with KOH(aq) enables determination of
the percentage of trioxoimidazolidine rings in products [2]:
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O
C
R N
O
C
C
N R
O
+
O O
R HN C N
KOH
C C OK + H2O
(2)
R
O
Based on this method it has been demonstrated that upon reaction of PA with 1
equivalent of EO at 40 °C in DMF regardless of amount of catalyst about 65 mole %
of trioxoimidazolidine rings remains preserved in the product. When the temperature
of reaction is increased to 70 °C further diminishing of ring percentage to 25 mole %
is observed.
The ring percentage in products obtained in reaction of PA with 2 equivalents of EO or
PO in absence of solvent at the catalyst level higher than 0.03 mole/mole PA at 40 °C
varies from 100 to 30 mole %. When temperature of the process is increased to 80°C
the ring percentage increases to 60 mole % regardless of the concentration of the catalyst.
The reaction of PA with excess of EO also result in trioxoimidazolidine ring opening,
regardless of the presence of solvent, amount of catalyst (0-0.144 mole TEA / mole
PA) or temperature of process (25-70 °C). In case of reactions conducted at 1: ≥ 3
molar ratio of the substrates, the products contain 3 moles of fragments originated
from EO ring opening (oxyethylene) per mole of PA. The product obtained from PA
and 3 equivalents of EO precipitates from the reaction mixture and does not react
with excess of oxirane [2]. Those products contain 22-60 mole % of preserved trioxoimidazolidine rings. The highest ring percentage was found in products of reactions in
absence both of solvent and catalyst.
The reactions of PA with 3-8 molar excess of PO were performed without catalyst and
result in formation of N,N’-bis(2-hydroxypropyl) parabanate regardless of the temperature of the process. In presence of TEA the trioxoimidazolidine rings undergo opening
already at 35-40 °C. The products contain 60-85 mole % preserved ring, however the
higher excess of PO, the more rings remain preserved in products. At PA to PO 1:3 and
1:4 molar ratio the products still contain secondary amide groups, while higher excess
of PO leads to products with only ternary amide groups, like in (VI):
CH2CH O
R
H
x
OO
C CN
C O
O CH CH2 z N CH2 CH O
R
R
(VI)
y
H
Reactions of PA with excess of PO at 70-80 °C also result in partial decomposition of
trioxoimidazolidine rings (the amount of preserved rings is maintained at the level of
70-85 mole %). The products still contain secondary amide groups even at 1:8 molar
ratio of substrates.
The reaction between PA and AC can be conducted without solvent, because PA is
well soluble in carbonates at 120-180 °C. Upon the reaction the carbon dioxide is
released from reaction mixture [16] and the 2-hydroxyalkyl groups are included in the
product [12, 13].
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O
C
O
C
HN
C
O
NH + n H2C
O
CH R
C
O
- CO2
O O
H O CH2 CH zO C C N CH2 CH O zH
CH3
O
H
C O
CH3
(3)
O CH CH2 y N CH2 CH O H
x
CH3
(VII)
CH3
It has been found that N-(hydroxyalkyl) hydroparabanates and N,N’-bis-(hydroxyalkyl)
parabanates cannot be obtained in the reaction between PA and AC; the products
with preserved trioxoimidazolidine rings. During the reaction of PA with AC the consecutive processes of hydroxyalkyl derivatives with PA take place resulting in trioxoimidazolidine ring opening, which was described in [11-13]. In the reaction between
PA and 1 equivalent of AC in absence of catalyst the products have 0.6 equivalent of
oxyethylene units and 0.33 equivalents of oxypropylene units per mole of PA. The
isolated products contain primary and secondary amide groups, unreacted imide
groups and barely ca 2.3 mole % of preserved trioxoimidazolidine rings. During the
reaction between PA and PC the abnormal products are not formed, similarly to the
reaction of PA with PO [2].
Tab. 1. The comparison of reaction conditions and composition of products obtained
from PA and alkylene oxides or AC.
Catalyst
Loss of
reagent
[% wag.]
Number of PA rings
preserved in product
[mole %]
Percentage
of byproducts
[wt.-% ]
25 - 70
TEA and
no catalyst rows
should be
separated
not detected (≈
0)
29 - 100
with out or
don’t determined
110 - 160
K2CO3
7 ÷ 22
1.4 - 35
0 - 17
PO
DMF and
bulk reaction rows
should be
separated
25 - 70
TEA and
no catalyst rows
should be
separated
noy detected (≈
0)
22 - 100
0 - 37
PC
bulk reaction rows
should be
separated
140 - 180
DABCO
34 - 45
1.6 - 8
0 - 20
Temperature
[°C]
EO
DMF and
bulk reaction rows
should be
separated
EC
bulk reaction rows
should be
separated
Kind of
reagent
Solvent
The reaction of PA with AC at high starting molar ratio of substrates requires the
presence of catalyst, i.e. potassium carbonate for reaction with EC [11, 12] or diazabicyclo[2.2.2]octane (DABCO) for the reaction with PC [13] (Table 1). The products obtained from PA to PC 1:2 system contain secondary amide groups and slight
amount of imide groups, while the products obtained from EC contain additionally
primary amide groups.
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The products formed in the reaction between PA and EC at 1:2 molar ratio have low
percentage of trioxoimidazolidine groups (3-34 mole %). The percentage depends of
temperature of the process and amount of catalyst [12]. The products obtained at 110,
120 and 140 °C in presence of 0.06 mole catalyst / mole PA contain over 30 mole % of
PA rings, otherwise the ring percentage drops down below 5 mole %. Products from the
reaction with PC have 2-3 mole % of trioxoimidazolidine rings regardless the temperature of reaction (Table 1) [13].
Reactions of PA with 3-fold molar excess of EC or PC lead to products without primary
amide groups. Secondary amide and imide groups disappear in the products obtained
from the systems of PA to EC 1:8 and PA to PC 1:4. Structure of products is exemplified by formula (VII) [12, 13].
Tab. 2. Results of MALDI ToF determination of product obtained from PA : EC 1 : 12 in
the presence of 0.12 mole K2CO3 / mole PA at 160 °C.
Signal position
Signal intensity [%]
Probable structure of molecular ion
258.1
39.4
PA + 2EO + CH3OH + Na+
277.1
28.8
PA + 3EO + CH3OH + H+
302.1
50.0
PA + 3EO + CH3OH + Na+
321.1
57.5
PA + 4EO + CH3OH + H+
346.1
37.5
PA + 4EO + CH3OH + Na+
365.2
45.0
PA + 5EO + CH3OH + H+
390.2
25.0
PA + 5EO + CH3OH + Na+
409.6
24.2
PA + 6EO + CH3OH + H+
434.2
22.5
PA + 6EO + CH3OH + Na+
453.2
11.2
PA + 7EO + CH3OH + H+
478.2
18.1
PA + 7EO + CH3OH + Na+
497.3
8.1
PA + 8EO + CH3OH + H+
522.3
16.3
PA + 8EO + CH3OH + Na+
547.2
69.0
2PA + 6EO + CH3OH + Na+
566.2
11.9
PA + 9EO + CH3OH + Na+
591.4
5.0
2PA + 7EO + CH3OH + Na+
652.6
3.8
PA + 11EO + CH3OH + Na+
700.7
2.5
2PA + 10EO + CH3OH + H+
748.7
3.1
3PA + 8EO + CH3OH + Na+
PA – trioxoimidazolidine ring or the unit of its opening, EO – oxyethylene unit
In case of the products obtained from PA to EC 1:3 or 4 substrate molar ratio the percentage of trioxoimidazolidine rings does not exceed 6 mole %, while the larger EC
excess is used (1:8) the ring percentage increases above 20 mole % [12]. In the products obtained from PA and 3- and higher molar excess of PC, the number of preserved
trioxoimidazolidine rings slightly increases with increasing excess of PC and reaches 8
mole % at 1:10 molar ratio [13].
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Based upon the products analysis by MALDI ToF it has been found that products obtained from PA with excess of EC have 1-3 preserved units of PA (cyclic or opened),
however the highest percentage product contains only one such unit (Table 2). The
products from PA with larger amount of EC (higher than 3 moles per mole PA) cannot be
obtained due to irreversible removal of semiproduct (precipitating from the solution).
Thus the products of reaction of PA with excess of PO or EC cannot be compared.
Tab. 3. Results of MALDI ToF determination of product from PA : PO 1 : 8 in the
o
presence of 0.144 mole TEA/mole PA at temperature 80 C.
Signal position
Signal intensity [%]
Probable structure of molecular ion
134.2
17.5
DPG + H+
160.2
60.0
PO + TEA + H+
172
14.0
PA + PO + H+
188.2
16.3
DPG + CH3OH + Na+
204.2
27.5
PA + PO + CH3OH + H+
218.3
25.0
TEA + 2PO+ H+
228.2
11.2
PA + PO + CH3OH + Na+
230.3
4.7
PA + 2PO + H+
246.3
16.2
TRIPG + CH3OH + Na+
262.2
100
PA + 2PO + CH3OH + H+
273.2
11.9
PA + TEA + PO + H+
288
9.4
PA + 3PO + H+
304.3
10.0
TETRAPG + CH3OH + Na+
334.3
18.7
PA + 2PO + TEA + H+
361.3
7.5
PA + 2PO + TEA+ CH3OH + H+
387.4
11.9
PA + 3PO + TEA+ H+
406.4
7.5
PA + 5PO + H+
445.5
10.0
PA + 4PO + TEA + H+
507.5
5.5
PA + 5PO + TEA + H+
676.6
5.5
PA + 8PO + TEA + H+
PO - oxypropylene unit
However, the comparison of the products obtained from PA with 8-molar excess of PO
or PC indicates, that oligomeric products obtained from PO contain only one unit of PA
(cyclic or opened), while the product from PC have larger amount of PA units (2 and/or
3, see Tables 3 and 4).
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Tab. 4. Results of MALDI ToF determination of product from PA : PC 1:8 in the preso
ence of 0.140 mole DABCO/mole PA at temperature 180 C.
Signal position
Signal intensity [%]
Probable structure of molecular ion
150.2
76.6
PA + Na+
178.2
41.2
DPG+ CO2 + H+
190.3
27.5
DPG+ CH3OH + Na+
203.3
25.0
PA + PO + CH3OH + H+
216.3
22.5
PA + PO+ CO2 + H+
229.3
30.6
PA + PO + CH3OH + Na +
230.3
62.5
PA + 2PO + H+
246.3
26.2
TRIPG + CH3OH + Na+
261.4
31.9
PA + 2PO + CH3OH+ H+
275.4
68.1
PA + 2PO + CO2 + H+
287.4
31.9
PA + 3PO + H+
296.4
45.0
PA + 2PO + CO2 + Na+
311.4
36.2
PA + 3PO + Na+
331.4
20.9
2PA + PO + CO2 + H+
333.4
16.8
PA + 3PO + CO2 + H+
337.4
24.4
2PA + PO + CH3OH + Na+
351.4
100
PA + 3PO + CO2 + Na+
369.5
62.2
PA + 4PO + Na+
379.5
11.2
PA + 4PO + CH3OH + H+
387.5
15.6
PA + 3PO+ CO2 + CH3OH +Na+
409.5
52.5
2PA + 2PO+ CO2 + Na+
427.5
89.4
PA + 5PO+ Na+
467.5
12.5
2PA + 3PO + CO2 + Na+
485.6
59.4
PA + 6PO + Na+
504.7
18.1
PA + 5PO + CO2 + CH3OH + Na+
543.7
10
PA + 7PO + Na+
573.7
6.9
2PA + 5PO + CH3OH + Na+
671.8
5.6
PA + 9PO + CH3OH + H+
704.8
5.6
PA + 9PO + CO2 + Na+
754.9
5.0
4PA + 4PO + CO2 + Na+
CO2 – carbonate unit
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Also the products with 4 units of PA are present. Moreover, the products from PA and
PC have carbonate groups included at the level at most 1 carbonate unit per molecule of
the product.
Hydroxyalkylation of PA with oxiranes or AC is accompanied by side reactions resulting in
formation of ethylene glycol (EG) or propylene glycol (PG) and the products of consecutive
reaction between them and oxiranes or AC, i.e. diethylene glycol (DEG), triethylene glycol
(TRIEG), tetraethylene glycol (TETRAEG), dipropylene glycol (DPG), and tripropylene
glycol (TRIPG). The percentage of by-products obtained from PA:PO in 1:2 molar ratio is
at the level of 2-11 wt.-% as determined by GC. The side-product percentage decreases
for the high temperature process and the reaction at 70 °C leads to the products with
barely 2 wt.-% of glycols. The products obtained from starting molar ratio 1:3 and 1:4 contain 1 and 2 wt.-% of GDP, respectively, regardless the temperature or reaction. In the
products obtained from the PA to PO 1:8 system all three glycols (PG, DPG i TRIPG) are
present at the level of 15-37 wt.-%. The temperature of the process is crucial for byproduct percentage; the higher the temperature the more by-products are formed (Table
1).
In case of products of reaction between PA and PC at 1:2 molar ratio, the propylene glycol and polyglycols percentage is maintained at the level of 5-7 wt.-%, regardless the
temperature of the process. At higher excess of PC the percentage of side products increases from 5 to 20 wt.-%. However increase of temperature when using excess of PC
induces diminishing of by-product percentage by half [13].
Tab. 5. Thermal stability of reaction products PA with AC and PO based on thermal
analysis.
T5% [°C]
T10% [°C]
T20% [°C]
T50% [°C]
Temperature
of max.
decomposition [°C]
Entry
Reagent
Molar ratio
PA : AC
1.
EC
1 : 2*
190
210
230
260
250
2.
EC
1:2
170
200
220
265
250
3.
EC
1:3
170
200
230
260
245
4.
EC
1:4
135
170
210
250
240
5.
EC
1:8
170
200
210
270
240
6.
EC
1 : 12
180
210
240
300
260
7.
PC
1:2
180
210
230
270
280
8.
PC
1:8
130
160
200
260
295
9.
PC
1 : 10
190
210
240
280
300
10.
PC
1 : 12
120
150
195
250
295
11.
PO
1:8
160
180
200
250
280
* The product contains ca 35 mole % of preserved trioxoimidazolidine rings.
Products obtained from lower molar ratio of PA to EC are accompanied by EG below 4
mole %. At higher PA:EC ratio the products of reactions between EG and EC, DEG,
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TRIEG or TETRAEG are formed at the level of 18 wt.-%. When temperature of the reaction is increased, the percentage of those side-products decreases slightly [12].
The reaction between PA and AC are accompanied by loss of carbonate from reaction mixture due to their decomposition [16]. It has been noticed that loss of EC decreases upon increase of molar ratio of substrates, while loss of PC is independent
on starting molar ratio of substrates. Moreover, the loss of AC increases on increase
of temperature of reaction (especially for the reactions with PC) [13].
Products of reaction between PA and PC have remarkable high temperature stability
despite of low percentage of preserved trioxoimidazolidine rings. According to thermogravimetric profiles, the temperature of maximum decomposition falls into the region of 240-260 °C or 270-300 °C for the products obtained from PA with EC or PA
with PC, respectively (Table 5).
The product containing ca 35 mole % of preserved PA rings has similar thermal stability to the one with barely 3 mole % of the rings (Table 5). The same dependence is
observed for the products of reactions of PA with PO and PC. The maximum temperature of decomposition for the products obtained from PA to PO 1:8 (85 mole % of
preserved rings) equals to 280 °C, while for the product obtained from the analogous
system with PC instead of PO this temperature equals to 295 °C.
The esteramideimidetetraols obtained in reaction between PA and 8- or 12-molar
excess of EC or PC, respectively, were used as starting polyols for polyurethanes of
increased thermal stability. The density, viscosity, surface tension and refractive index at 20 °C are listed in Table 6.
Tab. 6. Physical properties of reaction products of PA with AC measured in temperature 20 °C.
Entry
AC
1.
2.
3.
4.
EC
EC
PC
PC
Initial molar ratio
PA : AC
1:8
1 : 12
1:8
1 : 12
nD
[-]
1.4936
1.4858
1.4706
1.4666
Density
[g / cm3]
1.2295
1.2092
1.0766
1.0498
Viscosity ⋅ 103
[N ⋅ s / m2]
547.41
500.35
258.86
157.09
Surface tension ⋅ 102
[N / m]
4.622
5.030
3.500
3.206
The foaming was performed with 4,4’-diphenylmethane diisocyanate and TEA catalyst. The amount of diisocyanate and water was adjusted to reach the OH:NCO molar
ratio of 1:1.12 + 1:1.57. The foams of the best thermal stability were obtained from
the polyol synthesized from PA and 12-molar excess of EC (EC12) with isocyanate
index 1.52 and 2.5 wt.-% of TEA (Table 7, comp. no 3) and with polyol obtained from
8-fold excess of PC (PC8) with isocyanate index 1.57 and 2.0 wt.-% of TEA (Table 7,
comp. no 5).
The apparent density of foams obtained with EC12 and PC8 were 54.24 and 44.70
kg/m3, and glass temperatures were 110 and 145°C (Table 8). These parameters are
characteristic for rigid foams [17].
The lowest water absorption (8 wt.-%) after 24 hours sinking at room temperature
was observed for the foam obtained with PC8, while that of the foams obtained with
EC12 was 20 wt.-% (Table 8).The foams from polyol EC12 shrink during heating at
150 °C and the maximal change reaches linear 10 %, while the foams obtained with
PC8 enlarge above linear 5 % (Table 8).
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Tab. 7. Parameters of Foaming Process.
A
C
E
C
P
C
Initial
molar
ratio
PA :
AC
in
tetrao
Percentage of
oxyakylene
units in
product
[mol / mol
1 : 12
Composition
[g/100 g of tetraol]
Composition No
9.24
1:8
5.23
Foaming process
Properties of
foams
just prepared
Isocyanate*
Water
Catalyst**
Molar
ratio
OH/NC
O
1
146
-
2.5
1 : 1.52
10
4
0
rigid
2
144
-
2
1 : 1.50
16
1.5
0
rigid
3
146
-
2
1 : 1.52
12
2.5
0
rigid
4
184
1.62
2
1 :1.54
10
31
18
rigid
5
188
1.62
2
1 : 1.57
10
25
20
rigid
time [s]
Creami Expa2ndi Dryi
ng
ng3
ng1
* 4,4’-diphenylmethane diisocyanate, ** triethylamine,
1 Time of Creaming: the time elapsed from the moment of mixing to the start of volume expansion;
2 Time of Expanding: the time from the start of expansion to the moment of reaching the sample final
volume;
3 Time of Drying: the time from reaching by the sample its final volume to the moment of loosing its
surface adhesion to powdered substances.
Tab. 8. Properties of Foams.
Water uptake (wt.-%)
Comp
No*
Density
(kg/m3)
after 5
min
after
3 hrs
after
14 hrs
Linear dimension change after heating at 150°C (%)
Length
Width
Thickness
after
20 hrs
after
40 hrs
after
20 hrs
after
40 hrs
after
20 hrs
after 40
hrs
1
54.24
13.56
16.31
19.66
6.18
7.27
0.43
1.28
9.38
10.20
5
44.70
4.01
5.37
8.33
-0.74
-1.48
-1.30
-1.30
-3.16
-3.16
* Comp No according to Table 7.
The foams heated for 30 days at 150, 175 and 200 °C were subjected to test of compression strength. Generally, the compression strength grew upon heating and the
highest increase (350%) was observed for the foams obtained with EC12 after heating in 150 °C. After heating at 175 °C it dropped down slightly.
Tab. 9. Thermal stability of polyurethane foams.
Comp No
T5% [°C]
T10% [°C]
T20% [°C]
T50% [°C]
Tmax [°C]
Glass transition
Tg [°C]
1
200
220
250
455
250
110.0
5
220
250
270
495
275
145.0
Derivatographic profile of polyurethane foams confirms their higher thermal stability;
the 5 % mass loss occurs at 200 and 220 °C, and temperature of maximal decomposition equals 250 and 275 °C for the foams obtained from EC12 and PC8, respec10
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tively. The lowest mass loss of foam during heating rise with temperature was observed for the product obtained from PC8 (150 °C - 7 wt.-%, 175 °C - 20 wt.-%, and
200 °C - 30 wt.-%, Table 9). The mass loss of the foams obtained with EC12 is much
larger (Table 9).
Conclusions
The reactions between stoichiometric amount of parabanic acid and oxiranes lead to
low-molecular weight products: N-(2-hydroxyalkyl) hydroparabanates and N,N’-bis(2hydroxyalkyl) parabanates, the products with preserved trioxoimidazolidine rings.
When excess of oxirane is applied a mixture of products is formed containing the
units originated from parabanic acid ring opening.
The reactions between parabanic acid and alkylene carbonates lead to the linear oligomeric products containing the fragments of parabanic acid ring opening. The percentage of cyclic parabanic acid units in products varies between 1.4 and 35 mole %.
Upon the reaction between parabanic acid and ethylene oxide, regardless of the molar ratio of substrates the products contain formally only three oxyethylene units per
one parabanic acid (trioxoimidazolidine ring or the product of its opening). Analogous
reactions with ethylene carbonate lead to the products of variable number of those
groups.
Reactions of parabanic acid with alkylene carbonates give products with up to 4
parabanic acid units (cyclic or opened), while in the products of reactions with propylene oxide instead of propylene carbonate only one parabanic acid unit is present.
Hydroxyalkylation of parabanic acid with oxiranes and alkylene carbonates are accompanied by side-products; ethylene or propylene glycols and the products of the
consecutive reactions between them and oxiranes or alkylene carbonates.
The products of hydroxyalkylation of parabanic acid with alkylene carbonates or
oxiranes have high thermal stability, the higher for those obtained from parabanic
acid and propylene carbonate than from parabanic acid and propylene oxide despite
the lower percentage of preserved trioxoimidazolidine rings in the former.
Experimental
Synthesis
N-(2-hydroxyethyl)
and
N-(2-hydroxypropyl)
hydroparabanates,
N,N’-bis(2hydroxyethyl) and N,N’-bis(2-hydroxyethyl) parabanates, as well as the products of
reaction between PA and ethylene carbonate (EC) and propylene carbonate (PC) at
1:1 to 1:10 molar ratio were obtained and analyzed according to procedures published in [1,2, 11-13].
-Foam Preparation
Attempts at foaming the modified tetraols were carried out in small 250 cm3 test cups
at room temperature. To 5 g of a tetraol, 0.1 g of surfactant (Silicon 5340, Houdry
Hülls), 0.0-3.0 % wt. of triethylamine (TEA) catalyst (pure, Avocado, Germany), and
2-4 % wt. of water were added. After careful mixing of the components, a preweighed amount of 4,4’ diphenylmethane diisocyanate (Merck) was added, calculated as described in [18]. The amounts of diisocyanate and water were adjusted to
give OH:NCO molar ratio varying from of 1:1 to 1:1.8. Each composition was vigor11
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ously mixed until it started to cream (see Table 7). The samples for testing were cut
out from the foams thus obtained after ca. 48 hrs.
Analytical Methods
MALDI TOF (Matrix-Assisted Laser Desorption / Ionization Time of Flight) were obtained on Voyager-Elite Perseptive Biosystems (USA) mass spectrometer working at
linear mode with delayed ion extraction, equipped with nitrogen laser working at 337
nm. The method of laser desorption from matrix was used with 2,5-hydroxybenzoic
acid in THF at 10 mg/cm3 concentration. The samples were diluted with methanol to
1 mg/cm3, followed by addition of 10 mg/cm3 NaI in acetone. Therefore in some
cases the molecular ion weights were increased by the weight of Na+, H+ and
CH3OH.
Chromatographic analysis of by-products, i.e. ethylene glycol (EG) and consecutive
products of its reactions with EO, propylene glycol (PG) and products of its reactions
with PO were performed using a gas chromatograph HP 4890A (Hewlett Packard,
Ringoes, NJ, US) with FID detector and HP1 30 m x 0.53 mm column packed with
crosslinked methylsiloxane film of 1.5 μm thickness. Initial temperature was 50 °C,
heating rate: 20 °C/min, end temperature: 220 °C, time of heating at 220 °C: 6 min,
loader temperature: 250 °C, detector temperature: 300 °C. The samples were dissolved in methanol (0.01 M). Internal reference was cyclohexanone. Percentage of
diols and polyols were calculated according to calibration curves as described in [12].
Thermal analyses (DTA, DTG i TG) of esteramideimidetetraols and polyurethane
foams were performed in ceramic crucibles at 20-1000 °C temperature range, with
100 min registration time, 200 mg sample, under air atmosphere with Paulik-PaulikErdey derivatograph, MOM, Hungary.
The following properties of esteramideimidetetraols have been determined: pycnometer density [19], refractive index, Höppler viscosity [20], and surface tension by ring
detach method [21]. All measurements were made in temperature range 20-80 °C.
The following properties of foams were determined: apparent density [22], water uptake [23], linear shrinkage [24] including changes in linear dimensions before and
after heating at 100 ºC for 4 hrs, glass transition temperature (by DSC), thermal stability as the mass loss after heating at 150, 175, and 200 °C for a month, and the
compression strength [25].
The differential scanning calorimetry (DSC) measurements were made using a
DSC822e Mettler Toledo instrument at 20-300 °C temperature range and 10 deg/min
heating rate under nitrogen atmosphere. The results were recorded as heat flow in
[W/g] versus temperature.
References
[1] Zarzyka-Niemiec, I.; Lubczak, J.; Ciunik, Z.; Wołowiec, S.; Ruman, T. Heterocycl.
Comm. 2002, 8, 559.
[2] Lubczak, J.; Zarzyka-Niemiec, I. J. Appl. Polym. Sci. 2004, 94, 317.
[3] Lubczak, J.; Zarzyka-Niemiec, I. Inter. J. Chem. Kinetics, 2006, 38, 399.
[4] Monson, L.; Dickson, W. U.S. Pat. 2 819 301 (1958).
[5] Pop. B U.S. Pat. 4 474 951 (1984).
[6] Ureno, E. Jap. Pat. 7 802 411 (1978), CA: 88, 153477c (1978).
[7] Romano, U.; Melis, U. Germ. Pat. 2 615 655 (1977).
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[8] Krimm, H.; Buysch, H.; Rudolph, M. Germ. Pat. 2 740 242 (1979).
[9] Kucharski, M.; Kijowska, D. J. Appl. Polym. Sci., 2001, 80, 1776.
[10] Kucharski, M.; Kijowska, D. J. Appl. Polym. Sci., 2003, 89, 104.
[11] Lubczak, J.; Zarzyka-Niemiec, I. e-Polymers, International Polymer Seminar Gliwice, P_028, 1-6 (2005).
[12] Lubczak, J.; Naróg, D.; Zarzyka-Niemiec, I. J. Appl. Polym. Sci. 2006, 100, 1443.
[13] Zarzyka-Niemiec, I. Polimery 2006 (reviewed).
[14] Lubczak J.; Zarzyka-Niemiec I. Polimery, 2006, 51, 305.
[15] Lubczak J.; Zarzyka-Niemiec I. Polimery, 2005, 50, 383.
[16] Clements, J.; Reactive Applications of Cyclic Alkylene Carbonates, http://www.
huntsman.com/index.cfm. PageID=1201
[17] Wirpsza, Z.; Poliuretany, WNT, Warsaw,1991 (in polish).
[18] Kijowska, D.; Kucharski, M. J. Appl. Polym. Sci., 2004, 94, 2302.
[19] Kowalski, P. Laboratory of organic chemistry, WNT, Warsaw 2004, (in Polish).
[20] Kocot-Bończak, D. Laboratory experiments in physical chemistry, PZWL, Warsaw, 1977 (in polish).
[21] Dryński, T. Laboratory experiments in physic, PWN, Warsaw, 1967 (in polish).
[22] Polish (European) Standards: PN-EN ISO 845.
[23] Polish (European) Standards: PN-EN ISO 2896.
[24] Polish (European) Standards: PN-EN ISO 2796.
[25] Polish (European) Standards: PN-93C/89071, ISO 884:1978.
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