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Some specific features of three dimensional copolymerization of methacrylic acid and hexahydro-1,3,5-triacrylyltriazine and their effect on the swelling of the crosslinked polyelectrolytes
Polymer Science U.S.S.R. Vol. 20, pp. 2200-2204. (~ Pergamon Press Ltd. 1979. Printed in Poland
0032-3950]78/0901-2200507.50]0
SOME SPECIFIC FEATURES OF THREE DIMENSIONAL COPOLYMERIZATION OF METHACRYLIC ACID AND HEXAHYDRO-1,3,5-TRIACRYLYLTRIAZINE AND THEIR EFFECT ON THE SWELLING OF THE CROSSLINKED POLYELECTROLYTES* N. N. Kvz~x~sov,~, K. P. PAPVliOVA, T. D. :MVl~AV'~VA, G. V. BILIBI~A and V . I. ANDREYEVA Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences (Received 3 August 1977)
The effect is studied of the conditions of heterogeneous copolymerization of methacrylic acid and hexahydro-l,3,5.ttiacrylytriazine (the "quality" of the solvent, the concentration of the monomer mixture and the quantity of crosslinking agent), o n swelling of the crosslinked polyelectrolytes and on formation of heterogeneous porosity. IT has been shown previously that when methacrylic acid (MA) is copolymerized with hexahydro-l,3,5-triacrylyltriazine (HTA) in water or aqueous acetic acid (AA), when the concentration of the monomer mixture is low the reaction occurs under heterogeneous conditions [1]. At a certain critical, low degree of conversion, and concentration of HTA, phase separation occurs in the reaction mixture on the microscopic level, with formation of a dispersion. Structurization of the latter leads to formation of crosslinked polyelectrolytes (CPEs), with heterogeneous porosity in the hydrated state. In the present paper we report the results of a study of the effect of the copolymerization conditions on swelling of the CPEs. Distinctive features of copolymerization of MA and H T A in aqueous AA are that when the copolymer separates as a new phase it is in a highly hydrated state, and that structurization of the dispersion occurs when the concentration of H T A in the reaction mixture is low. Therefore because of the high mobility of the chains between network points the porosity is latent in the ungelled material disappearing as the matrix contracts during drying. When the H T A content is high, because of the rigidity of the matrix visible porosity results [2]. Crosslinked polyelectrolytes with visible porosity do not arouse practical interest because of their low mechanical strength. Copolymerization of MA with H T A produces a considerable exothermie effect, the rise in temperature being greatest in the "poor" solvent, i.e. 5% AA * Vysokomol. soyed. A2O: No. ~, 1957-1961, 1978. 2200
Three dimensional copolymerization of MA and t t T A
2201
(Fig. 1). In the more solvating solvent, 450/0 AA, in which micro-phase separat.ion begins at a more advanced degree of conversion, the auto-acceleration effect is very small, and in 50% DMF, in which the system is homogeneous, the effect is almost non-existent. This indicates that the high exothermic effect is primarily due to the heterogeneous nature of the three dimensional copolymerization. The auto-acceleration effect is to a considerable extent also dependent on the nature and quantity of the initiator. IZO F
4
"~ 10
~ ,ob •
P
.-~
so
#oX:_ zo
s. 20 60
120
Time ~ rain :FIG. 1
~
J
180
210
0.5
2
1.0
1.5
Inifiafop ~ w~. %
2.0
Fro. 2
FIG. 1. Thermometric curves of eopolymerization of M A a u d H T A in 50/0 (1), 30% (2) a n d 45% AA (3), and in 50% D M F (4). H T A content 12%, specific fraction of monomers in the reaction mixture, S°m=0.2, initiator-ammonium persulphate with sodium bisulphite. Fro. 2. Dependence of the gel point on initiator concentration in copolymerization of MA and H T A in: 5% (1), 20% (2) a n d 30% A A (3), and in 50% DMF (4).
A characteristic of the process is the position of the gel point (Fig. 2). It is seen that it is lowest and approximately the same in copolymerization in water and in 5-20% AA, b u t increases in 30% AA. Under homogeneous reaction conditions the gel point is two and a half to three times higher. Here, as would be expected, it increases as the initiator concentration is increased, whereas in AA it decreases slightly, probably because the mechanisms of formation of CPEs in homogeneous and heterogeneous systems are different. In crosslinked polyelectrolytes prepared in a poor solvent and when the monomer mixture is highly diluted, the porosity is very heterogeneous in the swollen state, and the internal surface area of the pores reaches 100-120 m2/ml of swollen material [3]. The swelling of these CPEs is dependent on the one hand on the size and number of pores in the ungelled material in the hydrated state, and on the other hand on the porosity of the material gelled b y crosslmkages. The contributions made to the swelling b y the non-gel and gel porosity, are dependent on the copolymerization conditions. The size of the gel pores decreases as the H T A content and the concentration of the monomer mixture increase. The effect of the non-gel porosity on the swelling of a CPE is determined b y the factors controlling the onset of micro-phase separation and formation of
2202
N.N.
KUZNETSOVA et al.
a dispersion. With the same composition of the monomer mixture the swelling coefficient, Ksw, changes considerably when the "quality" of the solvent is varied (Fig. 3). Copolymers prepared in a poor solvent (5% AA) and having a high internal surface area, swell to the greatest extent. In 30% AA which has a high solvating power with respect to an M A - H T A copolymer, microphase separation and formation of a dispersion occurs at high degrees of conversion, which results in decrease in the number of non-gel pores and hence to a greater contribution to swelling b y the gel porosity. The increase in Ksw with increase in initiator concentration is explained b y formation of a three dimensional network with chains of different molecular weight. The swelling coefficient of t h e porous CPEs increases also as the concentration of the monomer mixture is increased (Fig. 4), because structurization of the dispersion than occurs in the presence of a large volume of solvent.
6.Ksw 0- ~ ~
5..xJ 2.~
I
z
I
1.0
1.5
2.0
I
0.!
O~
Initialor, ~ % FIG. 3
O.J s& I
FIG. 4
FIG. 3. Dependence of K~w of H-form CPEs in water, on initiator concentration in copolymerization of MA and HTA in water (1), 5% (2), 20% (3) and 30% AA (4), and in 50% DMF (5). HTA content 12~/o, S°m----0"2. FIG. 4. Dependence of the degree of swelling, A, of H-form CPEs in water, on S°m. Solvent 5% AA, I-ITA content 12%. The variation in the degree of swelling of CPEs with change in the H T A content, is shown in Fig. 5. The decrease in swelling of the CP.Es as the ~ITA content is increased, as occurs with ordinary ion exchangers, shows that the gel porosity makes a large contribution to the swelling in the region of low H T A concentrations. Samples corresponding to this part of the curve are transparent when dry and are opalescent in the swollen state. The contribution of the nongel porosity to the swelling, increases as the H T A content is increased, and this is supported qualitatively b y increased opacity in the swollen state. Note that t h e swelling of the CPEs in the H-form is almost constant over a wide range of H T A concentrations (8-21% b y weight). This can be explained b y the fact
Three dimensional eopolymerization of MA and HTA
2203.
t h a t increase in the erosslinking density of the micro-gel particles, which is accompanied by reduction in the degree of hydration, must at the same time lead to increase in the non-gel porosity, as a result of structurization of the dispersion in a constant volume of solvent. For these CPE samples in the H-form, the quantity of water absorbed in the course of swelling (4-43 g of water pe~ gramme of absorbent), is close to the quantity of solvent in the original reaction 0 mixture (the specific fraction of monomers in the reaction mixture was Sin=0"2). The high degree of swelling of the CPEs in the H-form over a wide range of I-ITA contents, indicates the important part in swelling played by latent porosity, which is formed under conditions close to the conditions of hydration of CPEs in swelling in aqueous media.
usp m@ 2¢
b 16
c~
! •
@
•
2 4,
I
[
1
I
I
1
I
I
8
12
18
2O
8
12
16
20
HTA confenf, % FIe. 5. Dependence of the degree of swelling, A (a) and of the specific volume, vsp (b), of H-form CPEs in water, and of the H-Na-form, on H T A content in copolymerization in 5 (1, 1') and 30% AA (2), at S°n=0"2: /--swelling of tile H-form CPE in water, / ' - - s w e l l i n g of the H-Na-form CPE in a buffer at p H 6.8.
Samples containing 9-15~o of tITA have the greatest absorptive capacity with respect to serum albumen (SA) (Table). The entire range of HTA concentrations from 9-12% corresponds, however, to samples with latent, heterogeneous porosity suitable for sorption of proteins. Samples containing more than 21°/0 of HTA have visible as well as latent heterogeneous porosity. T h e y are opaque in the dry and swollen states, t h e y differ in having low mechanical: strength and are not of any practical interest. A CPE with heterogeneous porosity, prepared at S°m=0"3 (12% HTA, 5% AA), does not absorb SA. The curve of the dependence of swelling on the HTA content, for C P E s prepared by copolymerization in a solvent with greater solvating power, i.e. 30% AA, occupies a lower position on the graph. Samples that are opaque in the swollen state and have a more clearly defined, heterogeneous porosity,.
•2204
~ . N. KUZNETSOVA et al.
a r e f o r m e d w h e n t h e H T A c o n c e n t r a t i o n is h i g h ( 1 8 % a n d a b o v e ) . A l o w e r degree of swelling of the CPEs in the H-form and a low absorptive capacity w i t h r e s p e c t t o S A , i n d i c a t e a s m a l l e r p o r e size. T h e c u r v e o f t h e d e p e n d e n c e o f swelling of the CPEs in the H-form on the HTA content has the usual shape. SORPTION
O F S E R U M ALBUI%IEN B Y C A R B O X Y L I C UNDER
HTA %
6 9 12 15 18 21 27
CPEs (KMT-M)*,
OBTAINED
VARIOUS CONDITIONS
KMT-M-1 capacity degree of (mg/g) desorption, ~
KMT-i%I-2 capacity degree of (rag/g) desorption
No sorption
No sorption Ditto
900 1500 1000 700 600 350
100 80 85 85 95
400 500 700
85
100 7O No sorption
* KMT-M-1 (sorbent) was prepared in 5% AA, and KMT-M-2in 30% AA at S°m~0.2.
Copolymerization of MA a n d H T A was started at 20 °, in the presence of a m m o n i u m p e r s u l p h a t e and sodium bisulphite in a current of argon, the temperature inside the reaction vessel being monitored. All experiments were carried out under comparable conditions, w i t h the same volume of reaction mixture. After the t e m p e r a t u r e stopped rising the samples were heated at 95 ° for 0.5 hr, then ground and t r e a t e d with 0.5 ~ N a O H solution, IN HC1 solution a n d water. The swelling of the CPEs was determined gravimetrically, b y eentrifugation (grammes of w a t e r per gramme of ion exchanger). The coefficient of swelling was determined with t h e s a m e samples. The gel point was determined a p p r o x i m a t e l y as the time of cessation of the passage of bubbles of argon. The absorptive capacity with respect to serum albumen was determined under static conditions, from a 1N solution of an acetate buffer a t p H 4.7. Desorption took place in a 0.1 ~ solution of a phosphate buffer (pH 6.8). Translated by E. O. P~LLI~S REFERENCES 1. N. N. KUZNETSOVA, K. M. ROZHETSKAYA, B. V. MOSKVICHEV, L. K. SHATAYEVA, A. A. SELEZNEVA, I. M. OGORODNOVA a n d G. V. SAMSONOV, Vysokomol. soyed. A18:
355, 1976 (Translated in P o l y m e r Sci. U.S.S.R. 18: 2, 408, 1976) 2. K. DUSEK, P o l y m e r Networks (A. Y. Chormpff and S. Newman, Eds.) p. 245, New Y o r k - L o n d o n , 1971 3. Yu. S. NADEZHIN, L. K. SHATAYEVA, N. N. KUTZNETSOVA, A. V. SIDOROVICH a n d G. V. SAMSONOV, Vysokomol. soyed. A17: 448, 1975 (Translated in P o l y m e r Sei. U.S.S.R. 17: 2, 521, 1975)
0032-3950]78/0901-2200507.50]0
SOME SPECIFIC FEATURES OF THREE DIMENSIONAL COPOLYMERIZATION OF METHACRYLIC ACID AND HEXAHYDRO-1,3,5-TRIACRYLYLTRIAZINE AND THEIR EFFECT ON THE SWELLING OF THE CROSSLINKED POLYELECTROLYTES* N. N. Kvz~x~sov,~, K. P. PAPVliOVA, T. D. :MVl~AV'~VA, G. V. BILIBI~A and V . I. ANDREYEVA Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences (Received 3 August 1977)
The effect is studied of the conditions of heterogeneous copolymerization of methacrylic acid and hexahydro-l,3,5.ttiacrylytriazine (the "quality" of the solvent, the concentration of the monomer mixture and the quantity of crosslinking agent), o n swelling of the crosslinked polyelectrolytes and on formation of heterogeneous porosity. IT has been shown previously that when methacrylic acid (MA) is copolymerized with hexahydro-l,3,5-triacrylyltriazine (HTA) in water or aqueous acetic acid (AA), when the concentration of the monomer mixture is low the reaction occurs under heterogeneous conditions [1]. At a certain critical, low degree of conversion, and concentration of HTA, phase separation occurs in the reaction mixture on the microscopic level, with formation of a dispersion. Structurization of the latter leads to formation of crosslinked polyelectrolytes (CPEs), with heterogeneous porosity in the hydrated state. In the present paper we report the results of a study of the effect of the copolymerization conditions on swelling of the CPEs. Distinctive features of copolymerization of MA and H T A in aqueous AA are that when the copolymer separates as a new phase it is in a highly hydrated state, and that structurization of the dispersion occurs when the concentration of H T A in the reaction mixture is low. Therefore because of the high mobility of the chains between network points the porosity is latent in the ungelled material disappearing as the matrix contracts during drying. When the H T A content is high, because of the rigidity of the matrix visible porosity results [2]. Crosslinked polyelectrolytes with visible porosity do not arouse practical interest because of their low mechanical strength. Copolymerization of MA with H T A produces a considerable exothermie effect, the rise in temperature being greatest in the "poor" solvent, i.e. 5% AA * Vysokomol. soyed. A2O: No. ~, 1957-1961, 1978. 2200
Three dimensional copolymerization of MA and t t T A
2201
(Fig. 1). In the more solvating solvent, 450/0 AA, in which micro-phase separat.ion begins at a more advanced degree of conversion, the auto-acceleration effect is very small, and in 50% DMF, in which the system is homogeneous, the effect is almost non-existent. This indicates that the high exothermic effect is primarily due to the heterogeneous nature of the three dimensional copolymerization. The auto-acceleration effect is to a considerable extent also dependent on the nature and quantity of the initiator. IZO F
4
"~ 10
~ ,ob •
P
.-~
so
#oX:_ zo
s. 20 60
120
Time ~ rain :FIG. 1
~
J
180
210
0.5
2
1.0
1.5
Inifiafop ~ w~. %
2.0
Fro. 2
FIG. 1. Thermometric curves of eopolymerization of M A a u d H T A in 50/0 (1), 30% (2) a n d 45% AA (3), and in 50% D M F (4). H T A content 12%, specific fraction of monomers in the reaction mixture, S°m=0.2, initiator-ammonium persulphate with sodium bisulphite. Fro. 2. Dependence of the gel point on initiator concentration in copolymerization of MA and H T A in: 5% (1), 20% (2) a n d 30% A A (3), and in 50% DMF (4).
A characteristic of the process is the position of the gel point (Fig. 2). It is seen that it is lowest and approximately the same in copolymerization in water and in 5-20% AA, b u t increases in 30% AA. Under homogeneous reaction conditions the gel point is two and a half to three times higher. Here, as would be expected, it increases as the initiator concentration is increased, whereas in AA it decreases slightly, probably because the mechanisms of formation of CPEs in homogeneous and heterogeneous systems are different. In crosslinked polyelectrolytes prepared in a poor solvent and when the monomer mixture is highly diluted, the porosity is very heterogeneous in the swollen state, and the internal surface area of the pores reaches 100-120 m2/ml of swollen material [3]. The swelling of these CPEs is dependent on the one hand on the size and number of pores in the ungelled material in the hydrated state, and on the other hand on the porosity of the material gelled b y crosslmkages. The contributions made to the swelling b y the non-gel and gel porosity, are dependent on the copolymerization conditions. The size of the gel pores decreases as the H T A content and the concentration of the monomer mixture increase. The effect of the non-gel porosity on the swelling of a CPE is determined b y the factors controlling the onset of micro-phase separation and formation of
2202
N.N.
KUZNETSOVA et al.
a dispersion. With the same composition of the monomer mixture the swelling coefficient, Ksw, changes considerably when the "quality" of the solvent is varied (Fig. 3). Copolymers prepared in a poor solvent (5% AA) and having a high internal surface area, swell to the greatest extent. In 30% AA which has a high solvating power with respect to an M A - H T A copolymer, microphase separation and formation of a dispersion occurs at high degrees of conversion, which results in decrease in the number of non-gel pores and hence to a greater contribution to swelling b y the gel porosity. The increase in Ksw with increase in initiator concentration is explained b y formation of a three dimensional network with chains of different molecular weight. The swelling coefficient of t h e porous CPEs increases also as the concentration of the monomer mixture is increased (Fig. 4), because structurization of the dispersion than occurs in the presence of a large volume of solvent.
6.Ksw 0- ~ ~
5..xJ 2.~
I
z
I
1.0
1.5
2.0
I
0.!
O~
Initialor, ~ % FIG. 3
O.J s& I
FIG. 4
FIG. 3. Dependence of K~w of H-form CPEs in water, on initiator concentration in copolymerization of MA and HTA in water (1), 5% (2), 20% (3) and 30% AA (4), and in 50% DMF (5). HTA content 12~/o, S°m----0"2. FIG. 4. Dependence of the degree of swelling, A, of H-form CPEs in water, on S°m. Solvent 5% AA, I-ITA content 12%. The variation in the degree of swelling of CPEs with change in the H T A content, is shown in Fig. 5. The decrease in swelling of the CP.Es as the ~ITA content is increased, as occurs with ordinary ion exchangers, shows that the gel porosity makes a large contribution to the swelling in the region of low H T A concentrations. Samples corresponding to this part of the curve are transparent when dry and are opalescent in the swollen state. The contribution of the nongel porosity to the swelling, increases as the H T A content is increased, and this is supported qualitatively b y increased opacity in the swollen state. Note that t h e swelling of the CPEs in the H-form is almost constant over a wide range of H T A concentrations (8-21% b y weight). This can be explained b y the fact
Three dimensional eopolymerization of MA and HTA
2203.
t h a t increase in the erosslinking density of the micro-gel particles, which is accompanied by reduction in the degree of hydration, must at the same time lead to increase in the non-gel porosity, as a result of structurization of the dispersion in a constant volume of solvent. For these CPE samples in the H-form, the quantity of water absorbed in the course of swelling (4-43 g of water pe~ gramme of absorbent), is close to the quantity of solvent in the original reaction 0 mixture (the specific fraction of monomers in the reaction mixture was Sin=0"2). The high degree of swelling of the CPEs in the H-form over a wide range of I-ITA contents, indicates the important part in swelling played by latent porosity, which is formed under conditions close to the conditions of hydration of CPEs in swelling in aqueous media.
usp m@ 2¢
b 16
c~
! •
@
•
2 4,
I
[
1
I
I
1
I
I
8
12
18
2O
8
12
16
20
HTA confenf, % FIe. 5. Dependence of the degree of swelling, A (a) and of the specific volume, vsp (b), of H-form CPEs in water, and of the H-Na-form, on H T A content in copolymerization in 5 (1, 1') and 30% AA (2), at S°n=0"2: /--swelling of tile H-form CPE in water, / ' - - s w e l l i n g of the H-Na-form CPE in a buffer at p H 6.8.
Samples containing 9-15~o of tITA have the greatest absorptive capacity with respect to serum albumen (SA) (Table). The entire range of HTA concentrations from 9-12% corresponds, however, to samples with latent, heterogeneous porosity suitable for sorption of proteins. Samples containing more than 21°/0 of HTA have visible as well as latent heterogeneous porosity. T h e y are opaque in the dry and swollen states, t h e y differ in having low mechanical: strength and are not of any practical interest. A CPE with heterogeneous porosity, prepared at S°m=0"3 (12% HTA, 5% AA), does not absorb SA. The curve of the dependence of swelling on the HTA content, for C P E s prepared by copolymerization in a solvent with greater solvating power, i.e. 30% AA, occupies a lower position on the graph. Samples that are opaque in the swollen state and have a more clearly defined, heterogeneous porosity,.
•2204
~ . N. KUZNETSOVA et al.
a r e f o r m e d w h e n t h e H T A c o n c e n t r a t i o n is h i g h ( 1 8 % a n d a b o v e ) . A l o w e r degree of swelling of the CPEs in the H-form and a low absorptive capacity w i t h r e s p e c t t o S A , i n d i c a t e a s m a l l e r p o r e size. T h e c u r v e o f t h e d e p e n d e n c e o f swelling of the CPEs in the H-form on the HTA content has the usual shape. SORPTION
O F S E R U M ALBUI%IEN B Y C A R B O X Y L I C UNDER
HTA %
6 9 12 15 18 21 27
CPEs (KMT-M)*,
OBTAINED
VARIOUS CONDITIONS
KMT-M-1 capacity degree of (mg/g) desorption, ~
KMT-i%I-2 capacity degree of (rag/g) desorption
No sorption
No sorption Ditto
900 1500 1000 700 600 350
100 80 85 85 95
400 500 700
85
100 7O No sorption
* KMT-M-1 (sorbent) was prepared in 5% AA, and KMT-M-2in 30% AA at S°m~0.2.
Copolymerization of MA a n d H T A was started at 20 °, in the presence of a m m o n i u m p e r s u l p h a t e and sodium bisulphite in a current of argon, the temperature inside the reaction vessel being monitored. All experiments were carried out under comparable conditions, w i t h the same volume of reaction mixture. After the t e m p e r a t u r e stopped rising the samples were heated at 95 ° for 0.5 hr, then ground and t r e a t e d with 0.5 ~ N a O H solution, IN HC1 solution a n d water. The swelling of the CPEs was determined gravimetrically, b y eentrifugation (grammes of w a t e r per gramme of ion exchanger). The coefficient of swelling was determined with t h e s a m e samples. The gel point was determined a p p r o x i m a t e l y as the time of cessation of the passage of bubbles of argon. The absorptive capacity with respect to serum albumen was determined under static conditions, from a 1N solution of an acetate buffer a t p H 4.7. Desorption took place in a 0.1 ~ solution of a phosphate buffer (pH 6.8). Translated by E. O. P~LLI~S REFERENCES 1. N. N. KUZNETSOVA, K. M. ROZHETSKAYA, B. V. MOSKVICHEV, L. K. SHATAYEVA, A. A. SELEZNEVA, I. M. OGORODNOVA a n d G. V. SAMSONOV, Vysokomol. soyed. A18:
355, 1976 (Translated in P o l y m e r Sci. U.S.S.R. 18: 2, 408, 1976) 2. K. DUSEK, P o l y m e r Networks (A. Y. Chormpff and S. Newman, Eds.) p. 245, New Y o r k - L o n d o n , 1971 3. Yu. S. NADEZHIN, L. K. SHATAYEVA, N. N. KUTZNETSOVA, A. V. SIDOROVICH a n d G. V. SAMSONOV, Vysokomol. soyed. A17: 448, 1975 (Translated in P o l y m e r Sei. U.S.S.R. 17: 2, 521, 1975)