Copolymerization heterogeneous

Heterogeneous copolymerization of acrylamide causes redistribution comonomers between phases I and II. This leads to a change of copolymer composition in phases I and II. As a result, the values of ri and change. This accounts for anomalous widening of the experimental composition distribution curves as compared with theoretical curves. 

The heterogeneous copolymerization of styrene and acrylonitrile in various diluents as reported by Riess and Desvalois (22). Although the copolymer composition in these studies was not strongly influenced by the diluent choice, the preferential adsorption of acrylonitrile monomer onto the polymer particles shifted the azeotropic copolymerization point from the 38 mole % acrylonitrile observed in solution to 55 mole % acrylonitrile. 

Myagchenkov and coworkers (23) reported that no reasonable reactivity ratios could be chosen for the heterogeneous copolymerization of acrylamide and maleic acid in dioxane. 

Heterogeneous combustion, 7 449-454 Heterogeneous copolymerization of acrylonitrile, 11 203—204 with VDC, 25 698-699 Heterogeneous enzyme systems, 10 255-256 Heterogeneous gas-solid catalytic reactions, 21 340-341 Heterogeneous Ideal Adsorbed Solution Theory (HIAST), gas separation under, 1 628, 629... 

Succinimide-group-earrying latex particles are another versatile reactive support (12). The fraction of active succinimide groups on the particle surface was measured to be about 1% of succinimide monomer charged for the heterogeneous copolymerization with diethylene glycol methacrylate. 

Heterogeneous Copolymerization. When copolymer is prepared in a homogeneous solution, kineiic expressions can be used to predict copolymer composition Bulk and dispersion polymerization are somewhat different since the reaction medium is heterogeneous and polymeri/aiion occurs simultaneously in separate loci. In bulk polymerization, for example, the monomer swollen polymer particles support polymerization within the particle core us well as on the particle surface, lit aqueous dispersion or emulsion polymeri/aiion the monomer is actually dispersed in two or three distinct phases a continuous aqueous phase, a monomer droplet phase, and a phase consisting of polymer particles swollen at Ihe surface with monomer. This affect the ultimate polymer composition because llie monomers are partitioned such that the monomer mixture in the aqueous phase is richer in the more water-soluble monomers than the two organic phases. 

Information on both homogeneous (17) and heterogeneous copolymerization of maleic anhydride and vinyl monomers is available (30). 

As shown in Figure 2, the rate of the heterogeneous copolymerization of styrene and maleic anhydride in benzene (8 = 9.2) is faster than the homogeneous copolymerization of these monomers in acetone (8 = 9.9). However, this rate decreases as the solubility parameter values of the solvents decrease in heterogeneous systems. Thus, the rate of copolymerization decreases progressively in xylene (8 = 8.8), cumene (8 = 8.5), methyl isobutyl ketone (8 = 8.4), and p-cymene (8 — 8.2). All of these rates were faster than those observed in homogeneous systems. The solubility parameter of the alternating styrene-maleic anhydride copolymer was 8 = 11.0. 

The shift from homogeneous to heterogeneous copolymerization was also noted in acetone-benzene mixtures. The rate was slow, and the system was homogeneous when a benzene (50)-acetone (50) mixed solvent (S = 9.6) was used, but rapid heterogeneous copolymerization was observed in a benzene (80)-acetone (20) mixed solvent (S = 9.3). 

Table I. Yields of Copolymers of Styrene and Maleic Anhydride Obtained by Heterogeneous Copolymerization in Benzene after 72 Hours at 50°C...

Macroradicals obtained by the heterogeneous copolymerization of styrene and maleic anhydride in poor solvents such as benzene were used to initiate further polymerization of selected monomers. This technique was used to produce higher molecular weight alternating copolymers of styrene and maleic anhydride and block copolymers. Evidence for the block copolymers was based op molecular weight increase, solubility, differential thermal analysis, pyrolytic gas chromatography, and infrared spectroscopy. 

The difference in formaldehyde equilibrium concentration between homogeneous and heterogeneous polymerization is large enough to indicate a difference in the physical state of cationic chain ends in the dissolved and in the crystalline polymer. Thus, Model B is ruled out. In the homopolymerization of trioxane and in the heterogeneous copolymerization with small amounts of dioxolane the active centers of chains which have precipitated from the solution predominantly are directly on the crystal surface (Model A). According to Wunderlich (20, 21), this is the first case in addition polymerization where Model A—simultaneous polymerization and crystallization—has been proved experimentally. 

One of the most prominent features in the heterogeneous copolymerization of trioxane is the occurrence of two different kinds of active centers—dissolved and crystalline copolymer cations. They have different copolymer reactivity ratios and different tendencies to depolymerize, i.e., different formaldehyde equilibrium concentrations. At first the formation of soluble copolymer with high dioxolane content did not raise much hope for obtaining a crystalline copolymer of good thermal stability from trioxane and dioxolane but the gradual depolymerization of the soluble copolymer proved to be a useful side reaction which greatly improved the situation. Eventually, the entire complicated process turned out to be quite favorable for the formation of a stable crystalline copolymer with the desired random distribution. 

The heterogeneous copolymerization of PEO with hexyl methacrylate (HMA) was also studied under 21,5-kHz ultrasonic irradiation [28]. The ultrasonic irradiation degraded PEO into macroradicals which initiated the polymerization of HMA and formed PEO-HMA. The copolymer was again identified as a block copolymer by the methods quoted above. 

Association is particularly noticeable in heterogeneous polymerizations. If the copolymer which is formed precipitates out of the reaction mixture, then the adsorption of the two monomers onto the precipitating polymers will be unequal. This adsorption process depends on the association in solution, which in turn depends on the solvent (or the dielectric constant of the system, to which the solvent contributes). The deviations in the reactivity ratios which are often observed in heterogeneous copolymerizations are thus not really due to the heterogeneity itself but originate from monomer association. 

Cheetham PL, Tabner BJ. A spin-trap study of the aqueous heterogeneous copolymerization of acrylonitrile and vinyl acetate. Eur Polym J 1993 29 451 54. 

Cazacu et al. carried out an heterogeneous copolymerization between D4 and a diphenyldichlorosilane, in the presence of minute amounts of water necessary to hydrolyze the chlorosilane before the redistribution reaction [169]. An anionite (ammonium resin or basic gel) was also introduced into the recipe to capture the HCl released during the reaction. Polymer yields were decreased to 50%, when the content of chlorosUanes was increased to 70%. 

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