Ethylene copolymerization solvent effects

Copolymerization is effected by suspension or emulsion techniques imder such conditions that TFE, but not ethylene, may homopolymerize. Bulk polymerization is not commercially feasible because of heat-transfer hmitations and explosion hazard of the comonomer mixture. Polymerizations typically take place below 100°C and 5 MPa (50 atm). Initiators include peroxides, redox systems (10), free-radical sources (11), and ionizing radiation (12). Mixtures of inert solvent and water can be used, where the polymerization occurs in the solvent medium, while the water serves to lower the viscosity of the mixture and to remove the heat of polymerization (13,14). 

Intaragamjon, N., Shiono, T, (ongsomjit, B and Praserthdam, P, (2006) Elucidation of solvent effects on the catalytic behaviors for [t-BuNSiMe2Flu]TiMe2 complex during ethylene/l-hexene copolymerization,... 

Solvent polarity influences the rate of copolymerization. Thus with increasing dielectric constant of the solvent, the copolymerization rate rises as a result of the increase in the dissociation constants of the active species. The apparent rate constant for the copolymerization of 2-hydroxy-4-(2,3-epoxypropoxy)benzophenone with phthalic anhydride, initiated by hexadecyltrimethylammonium bromide56), increases from 4.65 x 10 4 s 1 in o-xylene to 6.84x 10 4 s-1 in nitrobenzene. Hilt et al.S4) proposed a suitable model illustrating the effect of solvent polarity in the copolymerization of phthalic anhydride with ethylene glycol carbonate in a mixture of nitrobenzene and trichlorobenzene (Table 4). With increasing fraction of the more polar nitrobenzene, the rate of copolymerization increases. 

The Effect of Solvents. Both toluene and hexane were used as solvents in the copolymerization reactions. Normally, toluene is the solvent for metallocene catalytic polymerization of olefins, since both catalyst and MAO are soluble in toluene. Hexane and other aliphatic hydrocarbon solvents are typical solvents for Ziegler-Natta catalytic polymerization. They are poor solvents for MAO. The original idea of using hexane as solvent for copolymerization of ethylene and p-MS was to improve the morphology of the copolymer in order to facilitate the filtration and purifi-... 

Solvents influence the rate of free-radical homopolymerization of acrylic acid and its copolymerization with other monomers. Hydrogen-bonding solvents slow down the reaction rates. Due to the electron-withdrawing nature of the ester groups, acrylic and methacrylic ester polymerize by anionic but not by cationic mechanisms. Lithium alkyls are very effective initiators of a-methyl methacrylate polymerization yielding stereospecific polymers.Isotactic poly(methyl methacrylate) forms in hydrocarbon solvents. Block copolymers of isotactic and syndiotactic poly(methyl methacrylate) form in solvents of medium polarity. Syndiotactic polymers form in polar solvents, like ethylene glycol dimethyl ether, or pyridine. This solvent influence is related to Lewis basicity in the following order ... 

Ethylene oxide/styrene block copolymers have been further free-radical copolymerized with other ethylenically unsaturated compounds such as methyl methacrylate and methacrylic acid in benzene, tetrahydrofuran, and dimethylformamide (176). Correlations were made between reactivity ratio and solvent dielectric constant, as well as between solubility parameters of reaction solvent and growing polymer chains with marked effects apparent. Gel permeation chromatography of diblock and triblock copolymers based on polystyrene and poly(ethylene oxide) has revealed interesting molecular characteristics (177). Such block copolymers have an amphiphilic character. In aqueous solution, the polymers form spherical micells with a polystyrene core and a poly(ethylene oxide) outer sheath. The investigations used an aqueous-methanolic solution and were able to ascertain block copolymer structures and to estimate the impurities in the diblock copolymer. 

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