Porous structure of interpenetrating polymer networks obtained by the anionic mechanism from an oligoesteracrylate

3Polymer Science U.S.S.R. Vol. 27, No. 4, pp. 776-782, 1985 Printed in Poland

0032-3950/85 $10.00+ .00 © 1986 Pergamon Press Ltd.

POROUS STRUCTURE OF INTERPENETRATING POLYMER NETWORKS OBTAINED BY THE ANIONIC MECHANISM FROM AN OLIGOESTERACRYLATE* T. E. LIPATOVA, YE. S. SHEVCHUK and L. S. KUZ'MENKO Institute of Organic Chemistry, Ukr. S.S.R. Academy of Sciences (Received 29 June 1983)

The sorption of n-hexane on interpenetrating polymer networks obtained from oligoesteracrylate and the copolymer of styrene with divinylbenzene by the anionic mechanism of polymeraization has been studied. The specific internal surface and the total pore volume of the synthesized networks have been determined. It is shown that the characteristics of porosity are determined by the method used to obtain and treat the matrix network and also the special aspects of the formation of the penetrating network governed by Coulombic interactions of the charged fragments of the two networks. THE porous structure of a polymer network formed en its shaping gives an idea of the molecular mechanism of the formation of the polymer itself. Earlier [1] it was shown that, depending on the method of treating the polymer network formed by the mechanism o f "live" anionic polymerization, its porosity m a y be changed within quite wide limits. After deactivation of the active centres of the equilibrium "live" anionic network there remains unsaturation which then almost disappears on pre-polymerization in air. The conditions in which this process occurs determine the value of the porosity of the final product. Such a mechanism of network formation gives a high level of microheterogeneity in the systems as has been shown by small angle X-ray scattel studies [2]. The interpenetrating networks obtained by the anionic mechanism on the basis o f the oligoesteracrylate matrices and styrene with divinyl benzene (penetrating network) a r e also characterized by high microheterogeneity which, as follows from the data in reference [3], is associated with the special distribution of the components of the polymerization system: the distribution of a penetrating network in the oligoesteracrylate comes about in the f o r m of inclusions measuring hundreds to thousands o f Angstr6ms and more. Naturally the formation of the porous structure of the interpenetrating polymer network (IPN) depends on the structure of the matrix network a n d occurs under the influence of the structure of the penetrating network. In the present work we tried to trace the dependence of the porous structure of the I P N on the mode of synthesis and treatment of the oligoesteracrylate matrix network a n d the conditions of introducing the penetrating network and also to estimate the * Vysokomol. soyed. A27: No. 4, 696-701, 1985. 776

Porous structure of interpenetrating polymer networks quantitative

777

v a l u e o f t h e t o t a l p o r e v o l u m e in t h e n e t w o r k s o b t a i n e d a n d t h e i r s p e c i f i c

internal surface. As test objects we chose

the networks

obtained

from

ct,~-dimethylacryl-bis-(di-

~ethylene glycol) phthalate (OEA), copolymers of styrene with divinyi benzene and IPNs synthesized from the two above mentioned networks.

The individual spatial networks and IPNs were obtained by the anionic mechanism of polymerization in a multi-section vessel at a residual pressure of 0.13 Pa following the technique in reference [4]. As polymerization catalysts we used sodium naphthalinate prepared on a sodium wire in T H F by the technique in reference [5]. The concentration of catalyst in all experiments was 0.1 mole/l. F r o m the polymer networks obtained from O E A we synthesized IPNs in which the penetrating network was a copolymer of sytrene with divinyl benzene with a m o n o m e r ratio by volume 10 : I. The IPNs were synthesized in various ways. ?Jlethod A. As matrix we used the network obtained from O E A for a volumetric ratio oligomer : : s o ! v e n t = 1 : 1 treated by inclusion and dried in vacuo to constant weight. The dry network was subjected to swelling for two days in a mixture of styrene with divinyl benzene after which the excess m o n o m e r s were removed. The swollen oligoesteracrylate network was placed in a polymerization vessel connected to a vacuum apparatus and the m o n o m e r mixture penetrating into the matrix polymerized by the anionic mechanism. A l e t h o d B. The matrix network obtained by method A in the form of a gel taken immediately after polymerization was introduced into the mixture of styrene with divinyl benzene. The m o n o m e r mi*:~ure was changed three times in one day thus replacing the solvent in the gel by this mixture. Tile ,~ther operations are simi!ar to those applied in the case of synthesis by m e t h o d A. :Xlethod C. Unlike the first two in which for the synthesis of the I P N we used the preformed matrix network, in this case the 1PNs were obtained by the m e t h o d of successive polymerization of the components in one experiment. F o r this a solution of oligomer, the mixture of stytene and divinyl benzene a n d catalyst were placed in different sections of the reaction vessel, the ratio of oligomer to m o n o m e r mixture was equal to unity. After careful degassing of all the solutions all the catalyst was added to the oligomer and after a few hours the m o n o m e r mixture. After four days in the vessel a gel formed of reddish-brown colour. In synthesizing the I P N in the way described we started from the known premise [6l on the absence in the anionic mechanism of copolymerization of the acrylic and vinyl monomers, and from the data of [7] indicating that on formation of IPNs copolymerization of styrene with O E A is not observed. A f e t h o d D. The matrix network was obtained for a volumetric content of solvent six times greater than on synthesis by m e t h o d C. A heavily swollen curd-like mass instantly formed. Then to it in some experiments was added styrene a n d after 10 rain divinyl benzene while in others the styrene mixture with divinyl benzene with an additional portion of catalyst. F o r comparison in identical conditions we obtained polystyrene networks. All the networks obtained were subjected to inclusion with solvent, v a c u u m drying and then their porous structure studied. The porosity of the networks was studied by the sorption m e t h o d at 303 K and residual pressure 0.01 Pa in an apparatus similar to that described in reference [8]. As sorbate we used n-hexane in which the test samples do not swell. The a m o u n t of solvent sorbed by the polymer was evaluated from the increase in the weight of the polymer o n McBain balances with tungsten wire springs with a diameter of 0.2 mm. The springs were first calibrated a n d checked for the absence of hysteresis phenomena. Their sensitivity was within the limits 0.13-0.30 m m / m g .

F i g u r e 1 p r e s e n t s t h e s o r p t i o n i s o t h e r m s o f t h e i n d i v i d u a l m a t r i x n e t w o r k ( c u r v e 1), t.he p e n e t r a t i n g

n e t w o r k ( c u r v e 2) a n d a l s o t h e I P N s

obtained by methods

A and B

778

T.E. LIPATOVAet

al.

(curves 3 and 4 respectively). The Figure shows that the network obtained from OEA has a sorption curve characteristic of non-porous glassy sorbents. The data on X-ray diffraction at small angles for similar samples obtained earlier [2] point to the presence in them of microheterogeneous regions (pores) with a mean radius 40 A. However, despite the presence of pores the test samples practically over the whole interval of relative pressures do not sorb an inert solvent. We attribute this discrepancy in the results given by two independent methods to the influence of shrinkage phenomena on the structure of the network. In studies [9, 10] it was established that the polymer networks on OEA obtained by the mechanism of "live" anionic polymerization have high residual unsaturation (up to 30 7o) and distances between the nodes of the crosslink exceeding two to three times the size of the oligomer block. These features of the OEA-networks aIe due to the presence in them of a large number of negative charges making the network rigid and preventing the interaction of a certain part of the double bonds of the oligomer. However, in the course of post-polymerization treatment of the "live" polymer of OEA there is decay of the active centres and removal of the negative charges from the phthalate groups also with an affinity for an electron. As a result the oligomer blocks regairL the flexibility peculiar to them [11] and the ability to change the conformation of the chains especially on removal of the solvent. Tb.is apparently leads to further interactiort of the previously non-reacting C = C bonds and as a consequence fall in the residual tmsaturation of the networks and "tightening" of the structural carcass of the networks and convergence of the pore walls or even their complete closure as a result of which the pores become inaccessible for the n-hexane molecules in sorption studies. This is confirmed by the results of study [2] of small ~,ngle X-ray diffraction of OEA networks indicating fall in the level of the microheterogeneity of the networks on passing from the swollen to the dried samples. A similar shrinkage phenomenon of the polymer OEA network was observed by the authors of reference [12] on polymerization of the oligoesteracrylates by the radical' mechanism. Turning to the sorption data for the polystyrene network as Fig. 1 (curve 2) shows, we see that its porosity is considerably higher than that of the OEA network. The sorption isotherm of the polystyrene network has an S-shaped form characteristic of sorbents with mesopores and is mathematically described by the Brunauer-Emmett-Teller equation [13]. The porosity characteristics calculated from this equatiort for the polystyrene network are given in the Table and point to a relatively large number of pores in the sample which is apparently associated with the rigidity of the chains forming the polystyrene network. The IPN obtained by method A is characterized by an isotherm (Fig. 1, curve 3) having the form of a curve with saturation peculiar for uniform fine porous or microporous samples. Since the micropores are inaccessible for the penetration into them of a large amount of solvent, on sorption on such sorbents saturation very rapidly ensues For microporous sorbents one may evaluate quantitatively only the value of the global pore volume from the Dubinin-Radushkevich equation [14]. The value Wo calculated.

Porous structure of interpenetrating polymer networks

779

f r o m this equation for the I P N studied amounts to thousands of cm 3 per g of polymer and indicates that it represents a sorbent with undeveloped porosity. Earlier it was mentioned that the OEA-matrix before obtaining the IPN was included in the solvent-precipitant mixture. Inclusiort of the equilibrium "live" po'4'mer network leads to washing out from it of the solvent, the non-polymerized oligomer and the soluble polymer and to the appearance of regions of microheterogeneity with a mean size o f ~ 100 A [1]. Apparently, washing out of the soluble fragments gives an insignificant number of open pores into which penetrates a small amount of styrene with divinylbenzene. The undeveloped porosity of the matrix and also the low concentration of the second network determine the structure of the ]PN obtained by method A.

a ,,~mc;fe/#

OB-"

a

Z

C. ,,nmole ?

0,t(

-

0.7-

© l I; i

1?'51 Og

0.06 O.OZ ~

o 0.1

,/p 9"5

f

1.0

1

P~Po FIG. 1

F

0.5

1"0 P/Po

Fm. 2

Fic~. I. Sorption isotherms of n-hexane on polymer networks: 1-matrix network obtained from OEA: 2-copolymer of styrene with divinylbenzene; 3 - IPN obtained by method A; 4 - b y method B

FIG. 2. Sorption isotherms of n-hexane on IPNs obtained by method C on introducing the catalyst. ir~ one dose (1), by method D on introducing catalyst in one dose (2) and by method D for two dose introduction of catalyst (3). Much more developed is the porosity in the I P N synthesized by method B. The isotherm characterizing it (Fig. 1, curve 4) has an S-shaped form and may be calculated by the Brunauer-Emmett-Teller method. The results of the calculation presented in the Table indicate that the pore volume in the IPN obtained from the gel like matrix grows ~ 4 times as compared with the I P N of the same nature but obtained on a dry matrix. Evidently, where the matrix network is introduced on synthesis in the form of a gel with solvent, its structural carcass fixed by the conditions of preparation by the anionic mechanism persists and probably changes little on successive ousting of the solvent

780

T, E. LIPATOVAet

CHARACTERISTICS OF

THE POROSITYOF THE I P N s

al.

OBTAINED ON THE BASIS

OF OEA

AND THE

COPOLYMER~

OF STYRENE WITH DIVINYLBENZENE

Sample Copolymer of styrene with divinylbenzene IPN

]PN-1

IPN-2

Isotherm number in figures 5 (Fig. 3 (Fig. 4 (Fig. l (Fig. 2 (Fig.

1) 1) 1) 2) 2)

3 (Fig. 2)

Method of obtaining lPN

Content in of penetrating network,

Sspec~ 1"13.2/g

9.30 A B

C D Catalyst introduced in one procedure D Catalyst introduced as two doses

8.70 59-70 70.80

0.0165 0.0052 0.0182 0.1120 0.1327

75.65

0.1517

1 "56

2'60 25 25

]

Wo, cmZ/g

I 20

I

1

by the styrene-divinylbenzene mixture. At the sites filled with monomers forming the second network they are copolymerized with formation of a rigid polystyrene network which then prevents conformational changes in the network-matrix. As a result, the characteristics of the porosity of the I P N obtained by method B come close to those for the pure polystyrene network. Even more developed is the porosity of the IPNs obtained by methods C and D. As may be seen from Fig. 2 the sorption isotherms of such networks are diffuse S-shaped curves characterizing the IPNs as sorbents with pores with a size ranging from tens to several thousand Angstroms. The quantitative characteristics of the porosity of such I P N s calculated by the Brunauer-Emmett-Teller method indicate that the specific internal surface and the total pore volume in them exceed ~ 6-10 times the same values for the I P N s obtained by method B (Table). The considerable increase in the porosity of the samples synthesized by the methods C and D is due to the possibility with these methods on synthesis of introducing into the I P N a large quantity of the rigid penetrating network characterized by high porosity, In the samples the sorption isotherms of which axe presented in Fig. 2 the amount o f the second network is tens of times greater than in the IPNs obtained by methods A and B (Table). Since the formation of the OEA network takes place in presence o f m o n o m e r s forming the penetrating network the more flexible OEA network " a d a p t s " to the rigid polystyrene network so that the microheterogeneity of the matrix network which at present one cart only nominally call "matrixial" grows together with rise in the porosity of the whole system. The most developed porosity is shown by the I P N s obtained by method D (Fig. 2, curves 2 and 3). A characteristic feature of their synthesis is that the network-matrix is obtained in presence of a solvent the content of which is six times higher than with the other methods listed. This helps to ensure that the matrix formed had a level of microheterogeneity exceeding by two orders the latter for the network-matrices used in the

Porous structure of interpenetrating polymer networks

781

methods A, B and C [1]. Apparently this also accounts for the increase in the prososity of the IPN synthesized on such a matrix as compared with that obtained by method C. In addition, as the Table shows the porosity of the IPN is also influenced by the sequence of introduction into the reaction of the reagents. Thus, on formation of IPN-I (Fig. 2, isotherm 2) when the catalyst is introduced into OEA in one dose the imtiation of polymerization of styrene and the crosslinking of it by divinylbenzene come about only as a result of the passage of electrons from the charged groups of the matrix network to the monomers. This leads to fall in the general level of the Coulombic interactions in the system and helps to ensure that the penetrating network is formed either in the pores of the network-matrix or in regions directly contiguous with the matrix network. Unlike the IPN-I the penetrating network in IPN-2 is formed in presence of more intense Coulombic interactions since addition of a new protion of catalyst promotes the retention of the charges present on the network-matrix and the formation of new ones. This gives very stressed structures with large pores. Thus, the results of the sorption studies of polymer il~terpenetrating networks indicate that the degree of the porosity of the IPN is determi~led by the method of synthesis and treatment of the matrix network and also by the special nature of the way the penetrating network was obtained. Quantitative evaluation of the porosity characteristics of the networks studied showed that anionic IPNs with developed porosity may be obtained with the proviso that the matrix network is synthesized in presence of a large amount of monomers from which, will then be formed the penetrating network or synthesis is carried out in dilute solutions promoting formation of microporous matrix networks. As well as the microheterogeneity of the constituent networks an important contribution of the formation of porous IPNs is also made by the Coulombic interactions of the charged fragments of the network-matrix and penetrating network the level of which depends on the way the catalyst is introduced into the polymerizing system. In conclusion, the authors wish to thank L. V. Karabanova for assistance in carrying out the experiments. Translated by A. CROZV

REFERENCES 1. T. E. LIPATOVA, L. S. KUZ'MENKO, V. V. SHILOV and V. A. BOGDANOVICH, Kompozitsionnye polimeryne materialy (Composite Polymer Materials) No. 5, p. 26, Naukova dumka, Kiev, 1980 2. T. E. LIPATOVA, L. S. KUZ'MENKO, V. V. SHILOV and N. N. MINENKO, Vysokomol. soyed. A20: 2013, 1978 (Translated in Polymer Sci. U.S.S.R. A20: 9, 2261, 1978) 3. T. E. LIPATOVA, Ye. S. SHEVCHUK, V. V. SHILOV and V. A. BOGDANOVICH, Ibid. A23: 73, 1981 (Translated in Polymer Sci. U.S.S.R. A23: 1, 83, 1981) 4. T. E. LIPATOVA, G. S. SHAPOVAL, N. P. BAZILEVSKAYA and Ye. S. SHEVCHUK, Ibid. AI4: 2610, 1972 (Translated in Polymer Sci. U.S.S.R. A14: 12, 3040, 1972) 5. Idem., Ibid. A l l : 2280, 1969 (Translated in Polymer Sci. U.S.S.R. A l l : 10, 2594, 1969) 6. I. MITA, K. WATABLE, H. KABLE and T. AKATSU, Polymer J. 4: 271, 1973

782

L. K. SHATAYEVAet al.

7. T. E. LIPATOVA, V. V. SHILOV, N. P. BASILEVSKAYA and Yu. S. LIPATOV, Brit. Polymer J. 9: 159, 1977 8. A. A. TAGER and V. A. KARGIN, Kolloid. zh. 10: 455, 1948 9. T. E. LIPATOVA, G. S. SHAPOVAL, N. P. BASILEVSKAYA and Yu. S. SHEVCHUK, J. Polymer Sci., Polymer Syrup., No. 42, 11, 1973 -10. G. S. SHAPOVAL, Ye. S. SHEVCHUK and T. E. LIPATOVA, Sintez i fizikokhimiya polimerov (Synthesis and Physicochemistry of Polymers) No. 17, p. 3, Naukova dumka, Kiev, 1975 :11. A. A. BERLIN, T. Ya. KEFELI and G. V. KOROLEV, Poliefirakrilaty (Polyesteracrylates). p. 349, Nauka, Moscow, 1967 ;J2. A. A. BERLIN, T. Ya. KEFELI, Yu. M. FILIPPOVSKAYA and Yu. M. SEVERGIN, Vysokotool soyed. 2: 411, 1960 (Not translated in Polymer Sci. U.S.S.R.) :t3. S. B R U N N A U E R , P. EMMET and E. TELLER, J. Amer. Chem. Soc. 60: 309, 1938 t4. M. M. DUBININ, Ye. D. Z A V E R I N A and L. V. RADUSI-IKEVICH, Zh. fiz. khim. 21t 1351, i 947

,PolymerScienceU.S.S.R.Vol. 27, No. 4, pp. 782-788, 1985 Printed in Poland

0032-3950/85 $10.00+ .00 © 1986 Pergamon Press Ltd.

INFLUENCE OF THE ACIDITY OF THE IONOGENIC GROUPS OF A NETWORK POLYELECTROLYTE ON THE STRENGTH OF THE PROTEIN-POLYMER COMPLEX* L. K. SHATAYEVA, K. 1. RADZYAVICHYUSa n d G. V. SAMSONOV Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences (Received 29 June 1983)

The selectivity and reversibility of sorption of pepsin and x-chymotrypsinogen A on porous cation exchangers with sulpho-, phospho- and carboxyl groups have been studied. It is shown that the optimal conditions for the binding of protein to the network polyelectrolyte depend on the isoelectric point of the protein and the acidity of the functional groups of the polyelectrolyte. Rise in the acidity of the functional groups widens the range of the pH values of the solution in which the given protein-polymer complex is stable. As is k n o w n two types o f complexes of polyelectrolytes exist with p r o t e i n m a c r o m o l e rules: based o n soluble (linear) [1-3] a n d insoluble (network) [4, 5] polyelectrolytes. S t u d y of the n o n - s t o i c h i o m e t r i c p o l y m e r complexes showed that the stability of the p o l y c o m p l e x e s in salt solutions depends o n the chemical reactions of r e d i s t r i b u t i o n * Vysokomol. soyed. A27: No. 4, 702-706, 1985.