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Emulsion copolymerization of vinyl and diene monomers with surfactant comonomers
Polymer Science Vol. 33, No. 7, pp. 1361-1367, 1991 Printed in Great Britain
0965-545X/91 $15.00 + .00 © 1992 Pergamon Press Ltd
EMULSION COPOLYMERIZATION OF VINYL AND DIENE MONOMERS WITH SURFACTANT COMONOMERS* YE. B. MALYUKOVA, S. V. NAUMOVA, I. A . GRITSKOVA, A . N. BONDAREV a n d V. P. ZUBOV L o m o n o s o v Institute of Fine Chemical Technology, Moscow
(Received3 January 1991)
Cationic and anionic surfactant monomers differing in their surface activity and reactivity have been synthesized. Copolymerizationconditions involving the use of surfactant monomers were selected on the basis of a study of the colloid-chemical properties of surfactant monomers and emulsions of various monomers prepared in their presence. A study was made of the kinetics of copolymerizationof vinyl and diene monomers in the presence of the cationic and anionic surfactant monomers, and properties of the resultant lattice comonomers were investigated. It is shown that the use of surfactant monomers in the emulsion polymerizationof various monomers leads to a marked reduction in the emulsifierconcentrations and makes it possible to dispense with the use of other surfactants, whilst preserving the reactivity of the reaction systems. SPECIAL studies of the topochemistry of emulsion polymerization processes have been made by Medvedev and coworkers [1-3]. After systematic investigation of the kinetics of polymerization of vinyl monomers in the presence of various initiators and emulsifiers the cited authors formed concepts of how emulsion polymerization takes place in the region of adsorption layers on the surface of p o l y m e r - m o n o m e r particles (PMPs). The concepts in question were validated in studies of the emulsion copolymerization of vinyl monomers with ionogenic and surfactant comonomers. The copolymerization of vinyl monomers with ionogenic or surfactant monomers (SAMs) provides a means of modifying the properties of polymers and lattices and also results in greater stability of the reaction systems used in the synthesis of lattices. Moreover in the preparation of ecologically pure products it is possible in this way to reduce the degree of foaming and to use lower concentrations of the emulsifiers. The copolymerization of vinyl monomers with SAMs is thought to be a very promising procedure on account of the increased stability of the reaction systems along with the reductions in the emulsifier concentrations. The copolymerization of vinyl and diene monomers with SAMs has received little attention in the literature, and insufficient information is available with regard to the colloid-chemical properties of SAMs. Without such information it is difficult to select conditions appropriate for the copolymerization process conducted in their presence. Despite this a large number of SAMs of ionogenic and nonionogenic types have been synthesized [4--8]. According to data in the patent literature, lattices and polymers prepared in the presence of copolymerizing emulsifiers have properties superior to those of analogous lattices and polymers synthesized in the presence of saturated surfactants [9-18]. Yegorov and coworkers [19, 20] investigated the colloid-chemical properties of various SAMs and *Vysokomol. soyed. A33: No. 7, 1469--1475, 1991.
1361
1362
YE. B. MALYUKOVAet al.
found that their molecules contain reactive double bonds, along with all the colloid-chemical properties characteristic of saturated surfactants. These include the ability to lower surface tension and interracial tension, to act as stabilizers of hydrocarbon emulsions, and to form micelles in aqueous solutions at definite concentrations. To select an optimum SAM structure ensuring the synthesis of stable lattices up to high degrees of conversion of monomers, while reducing the emulsifier concentrations, we syntehsized cationic and anionic SAMs differing in their surface activity and in their reactivity [16, 24]. The use of cationic surfactants to stabilize lattices could make it possible to prepare dispersions containing positively charged polymer particles. However cationic surfactants are used only to a limited extent as emulsifiers in emulsion polymerization processes owing to the low degree of stability of the reaction and of the final latex. Various cationic SAMs were used by ourselves in the polymerization of vinyl and diene monomers [16-18]. It is known that the surface activity of a SAM and the reactivity ratio of the SAM and the principal monomer have a marked influence on mechanisms of emulsion polymerization and on the composition and properties of the copolymers. For instance, the following SAM based on N-alkylaceto-2-methyl-5-vinylpyridinium bromide (MVPA-R, where R = Clff--C12 ) is characterized by high surface activity and by its ability to stabilize oil-water emulsions [19]:
CH = CH2 BF
_~ CH~ N
I
CH 2 -- COOCIoHz~ MVPA-Dc
Note the high degree of dispersity of monomer emulsions e.g. of styrene, stabilized by MVPA-Dc, which, along with the main fraction of monomer drops (d = 10/zm) contains a fraction of drops with d < 1/~m, the number of which increases with time. The polymerization of styrene MMA and chloroprene in the presence of MVPA-Dc has a short induction period, and the reaction rate remains constant up to 75-90% conversion (Fig. 1); the emulsion remains stable during the synthesis right up to complete conversion of the monomer. At the same time if the same monomers are polymerized in the presence of a saturated cationic surfactant, such as cetyl pyridinium bromide (CPB) the reaction system suffers the loss of aggregate stability in the process, and the final lattices contain a coagulum amounting to 10% or more. The surface tension of the latex increases in the course of styrene polymerization in the presence of MVPA-Dc, reaching a level approximating to that of water at 10% conversion, i.e. if this degree of conversion is exceeded, there will be no SAM in the water. It can be seen from the results of the IR analysis and the turbidimetric titration data for products of the styrene-MVPA-Dc copolymerization, separated at different degrees of conversion, that the MVPA-Dc is consumed in the early stages of polymerization and forms block copolymers of MVPA-Dc with styrene. Moreover the kinetics of the SAM consumption is similar to the kinetics of the loss of SAM from aqueous phase in the reaction system. In addition, calculations of the copolymerization constants for styrene with MVPA-Dc result in values of rl = 0.2 and r2 = 2.0 [23]. These results show that highly stable lattices with the particle surface bearing a positive charge may be synthesized.
Emulsion copolymerization of vinyl and diene monomers with SAMs
1363
Yield, % 100
(a)
(c) 1
60
20 I
I
200
80O
I
I
~O Time, min
120
68
180
FIG. 1. Plots of the polymer yield versus time in the polymerizationof styrene (a), chloroprene (b) and MMA (c) in the presence of MVPA-Dc (1) and CPB (2). Surfactantconcentration--1 mass % in aqueous phase, phase ratio 1: 2.
Anionic surfactants are more extensively used in emulsion polymerization processes on account of their marked stabilizing ability which is less dependent on the pH of the medium than in the case of cationic surfactants. Moreover much information has been published with regard to anionic surfactant monomers [4, 5, 20, 22, 25-30]. In an earlier study we made a more detailed investigation of the colloid-chemical properties of low-reactivity anionic SAMs, taking as an example derivatives of sulphocinnamic acid (M-SCA-R) and high reactivity anionic SAMs. In the latter case we took sulpho derivatives of alkyl amides of methacrylic acid (AESM-1 and AESM-2) [22]. These were synthesized in line with the following schemes: () ~- ~ \~j
", ) ! [
-
--CH=CH--CO--OR dioxane.SO3 dichloroethane
MSO3--(~)- - C H
..cH-coo, .
I/=-C,,H:,,_,: tz=10; 12; M = K +, Na +, NH~*. / I~--NtlC:It:SOa--N.',,. ' CHz=C(CHa)~COC1 pyridinep R - - N \ 0..5°
C2H.ISt~aNa
CO--C(CHa)=CH-,
where R =---C10H21; ---C12H25(AESM-1). Isotherms of the surface and interfacial tension at the interfaces [aqueous solution-air, and aqueous solution-styrene (butyl acrylate)] were obtained for these SAMs, and their surface reactivity was calculated as well as the maximum adsorption and the area occupied at the interface by the SAM molecule. Among a series of SAMs--sulphocinnamic acid derivatives--the surface activity at the interfaces styrene-water and butyl acrylate-water was highest for the NH4-SCA-12, and for AESM-1. It can be seen from the data presented in Fig. 2 that the emulsions of styrene and butyl acrylate
YE. B. MALYUKOVAetal.
1364 n,,~ni, %/l~m
]
(b)
(o)
I
I
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!
t
20 ~
I
l
!
!
•
I
3 !
#
m
20
q I
lO
I
I
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oo
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I
I
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30
i I
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F[o. 2. Histograms of size distribution for drops of emulsions of styrene (a) and butyl acrylate (b) stabilized with 1 mass % of surfactant. (1)---NH4-SCA-12, (2)--AESM-1, (3)--AESM-2 and (4)----E-30. Phase ratio 1:2.
stabilized by these SAMs have a higher degree of dispersity than emulsions of the given monomers prepared in the presence of an anion-active emulsifier, sodium alkylsulphonate (E-30). Spontaneous formation of a microemulsion occurs at the styrene, butyl acrylate-water interfaces under static conditions in the presence of the SAMs. The latter process takes place much more readily if a SAM is introduced into the monomer phase. The rate of microemulsification at the interface is proportional to the solubility of the SAM in the hydrocarbon phase. All this is responsible for the high concentration of SAM in the surface layer of PMPs---the main zone of polymerization, and creates conditions conducive to copolymerization of the SAM with the principal monomers. The conversion-time curves in Fig. 3 are for the polymerization of styrene, butyl acrylate and chloroprene in the presence of the SAMs and (for comparison) in the presence of E-30, other conditions being identical. It can be seen that polymerization takes place with short induction periods and the reaction rates are constant up to 80-90% conversion in the presence of SAMS and at 40-50% conversions in the presence of E-30. In the presence of a SAM, the emulsion system is completely stable starting at 10% conversion, and no separation (into layers) even in a centrifugal field, while with E-30 separation of the emulsion occurs practically immediately after stirring and polymerization have stopped at low degrees of conversion, and the stability of the emulsion is low all the way to 40-50% conversions. It is worth noting that lattices were obtained with a SAM concentration 4--5 times lower than the
Emulsion copolymerization of vinyl and diene monomers with SAMs
1365
Yield, % tOg
(a)
1
(b)
(c) l
2 3 l,t
.2
12 3
q
5o
20 700
300
25 50 Time, rain
50
I00
F16.3. Time dependence of the polymeryield in the polymerizationof styrene (a), butyl acrylate (b) and chloroprene (c) in the presence of emulsifiers: K-SCA-12(1), AESM-1 (2), AESM-2(3) and E-30 (4).
E-30 concentration normally used, whilst maintaining the stability of the reaction system in the synthesis of the lattices. The determining role played by SAM ionogenic groups in stabilizing PMPs and lattices is evident from the results of a study of the g-potentials of polystyrene lattices obtained in the polymerization of styrene in the presence of K-SCA-12 initiated by potassium persulphate and azo-bisisobutyronitrile (AIBN). The synthesized lattices are similar as to values of their ~-potentials ( - 6 0 and - 5 8 mV, respectively). Plots of the rate of styrene polymerization, MM of the polymers, and latex particle diameters versus concentrations of the SAM and initiator are of the type that is normal for emulsion polymerization. Products of styrene polymerization in the presence of SAMs were investigated by infra-red. It was found that during polymerization the SAM enters the copolymer composition, and the rate of SAM consumption is highest in the early stages of conversion in the period in which PMPs are formed (Fig. 4). Surfactant monomers of types K-SCA-12, AESM-1 and a SAM based on sulphophenyl acrylate (SPA-12) with the formula [28]
CO--CH~CH~ where R = --CI0H21 ; --C12H25, M = Na +; K + were used in the polymerization of methyl- and ethyl acrylate, methyl methacrylate and chloroprene, and in the copolymerization of acrylic and methacrylic acid esters with unsaturated acids without the addition of other surfactants. This made it possible to reduce the emulsifier concentration by a factor of 2-3 whilst preserving the stability of the reaction system. With a lower surfactant concentration and also using various SAMs as surfactants [29, 30] we obtained polystyrene dispersions with a narrow distribution of particles according to size and with a high level of stability towards the action of electrolytes, temperature and redispersion. The experimental results show that the use of SAMs in the emulsion polymerization of various monomers makes it possible not only to reduce the emulsifier concentrations substantially, but also to carry out the process without adding any other surfactants, whilst preserving the stability of the
YE. B. MALYUKOVA et al.
1366
Amount of SAM, % 60 j,
f
20
I
J
I0
20
Styrene conversion, %
FIG. 4. Degree of incorporation of SAM in the copolymer composition versus styrene conversion. (1)--AESM-1, (2)--K-SCA-12.
reaction system. The resulting lattices are highly stable, and a practically complete absence of emulsifier from the aqueous phase was observed.
Translated by R. J. A. HENDRY REFERENCES
1. G. D. BEREZHNOI, P. M. KHOMIKOVSKII, S. S. MEDVEDEV and I. V. POLUYAN, Vysokomol. soyed. 6: No. 1, 79, 1964 (not translated in Polymer Sci. U.S.S.R.). 2. S. S. MEDVEDEV, Kinetika i mekhanizm obrazovaniya i prevrashcheniya makromolec (Kinetics and Mechanism of the Formation and Transformation of Macromolecules). Moscow, 1968. 3. S. S. MEDVEDEV, I. A. GRITSKOVA, A. V. ZAIKOV, L. I. SEDAKOVA and G. D. BEREJNOI, J. Macromolec. Sci. A7: No. 3,715, 1973. 4. K. TAUER, K. H. GOEBEL, S. KOSMELLA, J. NEELSEN and K. STAI-ILER, Plaste und Kautsch. 35: No. 10, 373, 1988. 5. CHEN SHOW-AN and CHANG HERN-SHOW, J. Polymer Sci. Polymer Chem. Ed. 23: No. 10, 2615, 1985. 6. K. ITO, S. YOKOYAMA and F. ARAKAWA, Polymer Bull. 16: No. 4, 345, 1986. 7. J. DICKSTEIN, J. Am. Chem. Soc. Polymer Preprints 27: No. 1,427, 1986. 8. R. V. OTTEWILL, R. SATGURUNATHAN, A. F. WAITE and M. J. WESTBY, Brit. Polymer J. 19: 435, 1987. 9. M. ABE and M. NAGATA, Japan Pat. 50-154745, 1975; Zh. Khim. 3: No. 9, 82, 1978. 10. K. KOZUKA and Sh. KABAYASI-II, U.S.A. Pat. 3980622, 1975; Zh. Khim. 2: No. 12, 51, 1977. 11. T. INAGAKI and T. NAKAYAMA, Japan Pat. 57-53503, 1982; Zh. Khim. 2: No. 2, 78, 1983. 12. Kh. SAKAI, S. KI-IAMADA and I. YAMANAKA, U.S.A. Pat. 3781248, 1973; Zh. Khim. 2: No. 1, 48, 1975. 13. S. M. SAMOUR CALLO and M. C. RICHARDS, U.S.A. Pat. 3879447, 1972; Zh. Khim. 3" No. 3, 93, 1973. 14. J. DICKSTEIN, U.S.A. Pat. 4075411, 1975; Zh. Khim. 3: No. 19, 82, 1978. 15. T. TATINAI, N. IMAI, D. TAKEURI and A. VADA, Japan Pat. 56-4308, 1974; Zh. Khim. 3: No. 3, 53, 1983. 16. Ye. B. MALYUKOVA, G. K. ZALYGINA, I. A. GRITSKOVA, A. N. PRAVEDNIKOV, V. V. YEGOROV and V. P. ZUBOV, U.S.S.R. Pat. 1159932, Byull. Izob. No. 13, 1985. 17. V. V. YEGOROV, Yu. N. ORLOV, V. P. ZUBOV, I. A. GRITSKOVA and Ye. B. MALYUKOVA, U.S.S.R. Pat. 1174428; Byull. Izob. No. 25, 1985. 18. Yu. I. ORLOV, V. V. YEGOROV, Ye. B. MALYUKOVA, I. A. GRITSKOVA and V. P. ZUBOV, U.S.S.R. Pat. 1162787; Byull. Izob. No. 23, 1985.
Emulsion polymerization of hydrophobic m o n o m e r s
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19. V. V. YEGOROV, G. A. SIMAKOVA, Ye. B. MALYUKOVA, G. K. ZALYGINA, V. P. ZUBOV and I. A. GRITSKOVA, Moscow, 1983, p. 5, Dep. VINITI, 27.05.1983, No. 4170. 20. T. I. KURKINA, G. A. SIMAKOVA, Ye. B. MALYUKOVA, V. V. YEGOROV and V. P. ZUBOV, KoUoidn. Zhur. 50: No. 5,578, 1988. 21. V. V. YEGOROV, V. P. ZUBOV, S. G. KOSTROMIN and G. A. SlMAKOVA, U.S.S.R. Pat. 713868; Byull. Izob. No. 2, 1979. 22. V. A. KABANOV, V. P. ZUBOV, V. V. YEGOROV, S. V. NESMELOVA, Ye. B. MALYUKOVA, I. A. GRITSKOVA and A. N. PRAVEDNIKOVA, U.S.S.R. Pat. 1010059; Byull. Izob. No. 13, 1983. 23. Ye. B. MALYUKOVA, V. V. YEGOROV, V. P. ZUBOV, I. A. GRITSKOVA and A. N. PRAVEDNIKOV, Dokl. AN SSSR B28: No. 1, 69, 1986. 24. Yu. N. ORLOV, V. V. YEGOROV, V. P. ZUBOV, Ye. B. MALYUKOVA and I. A. GRITSKOVA, Vysokomol. soyed. B28: No. 1, 69, 1986 (not translated in Polymer Sci. U.S.S.R.). 25. J. L. GILLAUME, C. PICHOT and J. GUILLOT, J. Polymer Sci. Polymer Chem. Ed. 26: 1937, 1988. 26. B. W. GREEN, D. P. SHEETZ and T. D. FILLER, J. Colloid Interface Sci. 32: No. 1, 90, 1970. 27. Ye. B. MALYUKOVA, S. V. NESMELOVA, I. A. GRITSKOVA, A. N. PRAVEDNIKOV, V. V. YEGOROV, V. N. ZUBOV and V. A. KABANOV, Dokl. AN SSSR 284: No. 6, 1420, 1985. 28. V. A. KABANOV, V. P. ZUBOV and V. V. YEGOROV, U.S.S.R. Pat. 1010058; Byull. Izob. No. 13, 1983. 29. S. V. NAUMOVA, Ye. B. MALYUKOVA, Ye. S. RUSANOVA, L. I. VOLKOVA, I. A. GRITSKOVA and R. P. YEVSTIGNEEVA, U.S.S.R. Pat. 1268592; Byull. Izob. No. 41, 1986. 30. V. V. YEGOROV, V. P. ZUBOV, Ye. B. MALYUKOVA, S. V. NAUMOVA and I. A. GRITSKOVA, U.S.S.R. Pat. 1456412; Byull. Izob. No. 5, 1989.
PolymerScienceVol. 33, No. 7, pp. 1367-1374, 1991 Printed in Great Britain
0965--545X/91$15.00 + .00 © 1992 Pergamon Press Ltd
EMULSION POLYMERIZATION OF HYDROPHOBIC MONOMERS IN HIGHLY-DISPERSED EMULSIONS* I. A . GRITSKOVA, S. V. ZHACHENKOV, N. I. PROKOPOV a n d P. YE. IL'MENEV Lomonosov Institute of Fine Chemical Technology, Moscow (Received 4 January 1991) The main features of polymerization are described for hydrophobic monomers in highly dispersed emulsions prepared by various methods, using water- and oil-soluble initiators. It is shown that the dispersed composition of monomer emulsions affects both the main parameters of polymerization and properties of the end products (polymers and lattices).
IT APPEARS from the results of m a n y studies of the emulsion polymerization of hydrophobic m o n o m e r s that the main p a r a m e t e r s determining the course of polymerization and properties of the end products are the n u m b e r and the size distribution of the p o l y m e r - m o n o m e r particles (PMPs) [11. Before the start of the 1960s it was thought that PMPs form from emulsifier micelles that have * Vysokomol. soyed. A33: No. 7, 1476-1483, 1991.
PS 33:7-H
0965-545X/91 $15.00 + .00 © 1992 Pergamon Press Ltd
EMULSION COPOLYMERIZATION OF VINYL AND DIENE MONOMERS WITH SURFACTANT COMONOMERS* YE. B. MALYUKOVA, S. V. NAUMOVA, I. A . GRITSKOVA, A . N. BONDAREV a n d V. P. ZUBOV L o m o n o s o v Institute of Fine Chemical Technology, Moscow
(Received3 January 1991)
Cationic and anionic surfactant monomers differing in their surface activity and reactivity have been synthesized. Copolymerizationconditions involving the use of surfactant monomers were selected on the basis of a study of the colloid-chemical properties of surfactant monomers and emulsions of various monomers prepared in their presence. A study was made of the kinetics of copolymerizationof vinyl and diene monomers in the presence of the cationic and anionic surfactant monomers, and properties of the resultant lattice comonomers were investigated. It is shown that the use of surfactant monomers in the emulsion polymerizationof various monomers leads to a marked reduction in the emulsifierconcentrations and makes it possible to dispense with the use of other surfactants, whilst preserving the reactivity of the reaction systems. SPECIAL studies of the topochemistry of emulsion polymerization processes have been made by Medvedev and coworkers [1-3]. After systematic investigation of the kinetics of polymerization of vinyl monomers in the presence of various initiators and emulsifiers the cited authors formed concepts of how emulsion polymerization takes place in the region of adsorption layers on the surface of p o l y m e r - m o n o m e r particles (PMPs). The concepts in question were validated in studies of the emulsion copolymerization of vinyl monomers with ionogenic and surfactant comonomers. The copolymerization of vinyl monomers with ionogenic or surfactant monomers (SAMs) provides a means of modifying the properties of polymers and lattices and also results in greater stability of the reaction systems used in the synthesis of lattices. Moreover in the preparation of ecologically pure products it is possible in this way to reduce the degree of foaming and to use lower concentrations of the emulsifiers. The copolymerization of vinyl monomers with SAMs is thought to be a very promising procedure on account of the increased stability of the reaction systems along with the reductions in the emulsifier concentrations. The copolymerization of vinyl and diene monomers with SAMs has received little attention in the literature, and insufficient information is available with regard to the colloid-chemical properties of SAMs. Without such information it is difficult to select conditions appropriate for the copolymerization process conducted in their presence. Despite this a large number of SAMs of ionogenic and nonionogenic types have been synthesized [4--8]. According to data in the patent literature, lattices and polymers prepared in the presence of copolymerizing emulsifiers have properties superior to those of analogous lattices and polymers synthesized in the presence of saturated surfactants [9-18]. Yegorov and coworkers [19, 20] investigated the colloid-chemical properties of various SAMs and *Vysokomol. soyed. A33: No. 7, 1469--1475, 1991.
1361
1362
YE. B. MALYUKOVAet al.
found that their molecules contain reactive double bonds, along with all the colloid-chemical properties characteristic of saturated surfactants. These include the ability to lower surface tension and interracial tension, to act as stabilizers of hydrocarbon emulsions, and to form micelles in aqueous solutions at definite concentrations. To select an optimum SAM structure ensuring the synthesis of stable lattices up to high degrees of conversion of monomers, while reducing the emulsifier concentrations, we syntehsized cationic and anionic SAMs differing in their surface activity and in their reactivity [16, 24]. The use of cationic surfactants to stabilize lattices could make it possible to prepare dispersions containing positively charged polymer particles. However cationic surfactants are used only to a limited extent as emulsifiers in emulsion polymerization processes owing to the low degree of stability of the reaction and of the final latex. Various cationic SAMs were used by ourselves in the polymerization of vinyl and diene monomers [16-18]. It is known that the surface activity of a SAM and the reactivity ratio of the SAM and the principal monomer have a marked influence on mechanisms of emulsion polymerization and on the composition and properties of the copolymers. For instance, the following SAM based on N-alkylaceto-2-methyl-5-vinylpyridinium bromide (MVPA-R, where R = Clff--C12 ) is characterized by high surface activity and by its ability to stabilize oil-water emulsions [19]:
CH = CH2 BF
_~ CH~ N
I
CH 2 -- COOCIoHz~ MVPA-Dc
Note the high degree of dispersity of monomer emulsions e.g. of styrene, stabilized by MVPA-Dc, which, along with the main fraction of monomer drops (d = 10/zm) contains a fraction of drops with d < 1/~m, the number of which increases with time. The polymerization of styrene MMA and chloroprene in the presence of MVPA-Dc has a short induction period, and the reaction rate remains constant up to 75-90% conversion (Fig. 1); the emulsion remains stable during the synthesis right up to complete conversion of the monomer. At the same time if the same monomers are polymerized in the presence of a saturated cationic surfactant, such as cetyl pyridinium bromide (CPB) the reaction system suffers the loss of aggregate stability in the process, and the final lattices contain a coagulum amounting to 10% or more. The surface tension of the latex increases in the course of styrene polymerization in the presence of MVPA-Dc, reaching a level approximating to that of water at 10% conversion, i.e. if this degree of conversion is exceeded, there will be no SAM in the water. It can be seen from the results of the IR analysis and the turbidimetric titration data for products of the styrene-MVPA-Dc copolymerization, separated at different degrees of conversion, that the MVPA-Dc is consumed in the early stages of polymerization and forms block copolymers of MVPA-Dc with styrene. Moreover the kinetics of the SAM consumption is similar to the kinetics of the loss of SAM from aqueous phase in the reaction system. In addition, calculations of the copolymerization constants for styrene with MVPA-Dc result in values of rl = 0.2 and r2 = 2.0 [23]. These results show that highly stable lattices with the particle surface bearing a positive charge may be synthesized.
Emulsion copolymerization of vinyl and diene monomers with SAMs
1363
Yield, % 100
(a)
(c) 1
60
20 I
I
200
80O
I
I
~O Time, min
120
68
180
FIG. 1. Plots of the polymer yield versus time in the polymerizationof styrene (a), chloroprene (b) and MMA (c) in the presence of MVPA-Dc (1) and CPB (2). Surfactantconcentration--1 mass % in aqueous phase, phase ratio 1: 2.
Anionic surfactants are more extensively used in emulsion polymerization processes on account of their marked stabilizing ability which is less dependent on the pH of the medium than in the case of cationic surfactants. Moreover much information has been published with regard to anionic surfactant monomers [4, 5, 20, 22, 25-30]. In an earlier study we made a more detailed investigation of the colloid-chemical properties of low-reactivity anionic SAMs, taking as an example derivatives of sulphocinnamic acid (M-SCA-R) and high reactivity anionic SAMs. In the latter case we took sulpho derivatives of alkyl amides of methacrylic acid (AESM-1 and AESM-2) [22]. These were synthesized in line with the following schemes: () ~- ~ \~j
", ) ! [
-
--CH=CH--CO--OR dioxane.SO3 dichloroethane
MSO3--(~)- - C H
..cH-coo, .
I/=-C,,H:,,_,: tz=10; 12; M = K +, Na +, NH~*. / I~--NtlC:It:SOa--N.',,. ' CHz=C(CHa)~COC1 pyridinep R - - N \ 0..5°
C2H.ISt~aNa
CO--C(CHa)=CH-,
where R =---C10H21; ---C12H25(AESM-1). Isotherms of the surface and interfacial tension at the interfaces [aqueous solution-air, and aqueous solution-styrene (butyl acrylate)] were obtained for these SAMs, and their surface reactivity was calculated as well as the maximum adsorption and the area occupied at the interface by the SAM molecule. Among a series of SAMs--sulphocinnamic acid derivatives--the surface activity at the interfaces styrene-water and butyl acrylate-water was highest for the NH4-SCA-12, and for AESM-1. It can be seen from the data presented in Fig. 2 that the emulsions of styrene and butyl acrylate
YE. B. MALYUKOVAetal.
1364 n,,~ni, %/l~m
]
(b)
(o)
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!
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!
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F[o. 2. Histograms of size distribution for drops of emulsions of styrene (a) and butyl acrylate (b) stabilized with 1 mass % of surfactant. (1)---NH4-SCA-12, (2)--AESM-1, (3)--AESM-2 and (4)----E-30. Phase ratio 1:2.
stabilized by these SAMs have a higher degree of dispersity than emulsions of the given monomers prepared in the presence of an anion-active emulsifier, sodium alkylsulphonate (E-30). Spontaneous formation of a microemulsion occurs at the styrene, butyl acrylate-water interfaces under static conditions in the presence of the SAMs. The latter process takes place much more readily if a SAM is introduced into the monomer phase. The rate of microemulsification at the interface is proportional to the solubility of the SAM in the hydrocarbon phase. All this is responsible for the high concentration of SAM in the surface layer of PMPs---the main zone of polymerization, and creates conditions conducive to copolymerization of the SAM with the principal monomers. The conversion-time curves in Fig. 3 are for the polymerization of styrene, butyl acrylate and chloroprene in the presence of the SAMs and (for comparison) in the presence of E-30, other conditions being identical. It can be seen that polymerization takes place with short induction periods and the reaction rates are constant up to 80-90% conversion in the presence of SAMS and at 40-50% conversions in the presence of E-30. In the presence of a SAM, the emulsion system is completely stable starting at 10% conversion, and no separation (into layers) even in a centrifugal field, while with E-30 separation of the emulsion occurs practically immediately after stirring and polymerization have stopped at low degrees of conversion, and the stability of the emulsion is low all the way to 40-50% conversions. It is worth noting that lattices were obtained with a SAM concentration 4--5 times lower than the
Emulsion copolymerization of vinyl and diene monomers with SAMs
1365
Yield, % tOg
(a)
1
(b)
(c) l
2 3 l,t
.2
12 3
q
5o
20 700
300
25 50 Time, rain
50
I00
F16.3. Time dependence of the polymeryield in the polymerizationof styrene (a), butyl acrylate (b) and chloroprene (c) in the presence of emulsifiers: K-SCA-12(1), AESM-1 (2), AESM-2(3) and E-30 (4).
E-30 concentration normally used, whilst maintaining the stability of the reaction system in the synthesis of the lattices. The determining role played by SAM ionogenic groups in stabilizing PMPs and lattices is evident from the results of a study of the g-potentials of polystyrene lattices obtained in the polymerization of styrene in the presence of K-SCA-12 initiated by potassium persulphate and azo-bisisobutyronitrile (AIBN). The synthesized lattices are similar as to values of their ~-potentials ( - 6 0 and - 5 8 mV, respectively). Plots of the rate of styrene polymerization, MM of the polymers, and latex particle diameters versus concentrations of the SAM and initiator are of the type that is normal for emulsion polymerization. Products of styrene polymerization in the presence of SAMs were investigated by infra-red. It was found that during polymerization the SAM enters the copolymer composition, and the rate of SAM consumption is highest in the early stages of conversion in the period in which PMPs are formed (Fig. 4). Surfactant monomers of types K-SCA-12, AESM-1 and a SAM based on sulphophenyl acrylate (SPA-12) with the formula [28]
CO--CH~CH~ where R = --CI0H21 ; --C12H25, M = Na +; K + were used in the polymerization of methyl- and ethyl acrylate, methyl methacrylate and chloroprene, and in the copolymerization of acrylic and methacrylic acid esters with unsaturated acids without the addition of other surfactants. This made it possible to reduce the emulsifier concentration by a factor of 2-3 whilst preserving the stability of the reaction system. With a lower surfactant concentration and also using various SAMs as surfactants [29, 30] we obtained polystyrene dispersions with a narrow distribution of particles according to size and with a high level of stability towards the action of electrolytes, temperature and redispersion. The experimental results show that the use of SAMs in the emulsion polymerization of various monomers makes it possible not only to reduce the emulsifier concentrations substantially, but also to carry out the process without adding any other surfactants, whilst preserving the stability of the
YE. B. MALYUKOVA et al.
1366
Amount of SAM, % 60 j,
f
20
I
J
I0
20
Styrene conversion, %
FIG. 4. Degree of incorporation of SAM in the copolymer composition versus styrene conversion. (1)--AESM-1, (2)--K-SCA-12.
reaction system. The resulting lattices are highly stable, and a practically complete absence of emulsifier from the aqueous phase was observed.
Translated by R. J. A. HENDRY REFERENCES
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PolymerScienceVol. 33, No. 7, pp. 1367-1374, 1991 Printed in Great Britain
0965--545X/91$15.00 + .00 © 1992 Pergamon Press Ltd
EMULSION POLYMERIZATION OF HYDROPHOBIC MONOMERS IN HIGHLY-DISPERSED EMULSIONS* I. A . GRITSKOVA, S. V. ZHACHENKOV, N. I. PROKOPOV a n d P. YE. IL'MENEV Lomonosov Institute of Fine Chemical Technology, Moscow (Received 4 January 1991) The main features of polymerization are described for hydrophobic monomers in highly dispersed emulsions prepared by various methods, using water- and oil-soluble initiators. It is shown that the dispersed composition of monomer emulsions affects both the main parameters of polymerization and properties of the end products (polymers and lattices).
IT APPEARS from the results of m a n y studies of the emulsion polymerization of hydrophobic m o n o m e r s that the main p a r a m e t e r s determining the course of polymerization and properties of the end products are the n u m b e r and the size distribution of the p o l y m e r - m o n o m e r particles (PMPs) [11. Before the start of the 1960s it was thought that PMPs form from emulsifier micelles that have * Vysokomol. soyed. A33: No. 7, 1476-1483, 1991.
PS 33:7-H