Character of Active Centers in the Copolymerization of Epoxides with Cyclic Anhydrides

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Abstract
The conductivity of different catalytic and copolymerization systems which were used for the copolymerization of epoxide with cyclic anhydride catalyzed by a tertiary amine, ammonium salt, alkali salt, and the system tert-amine-proton donor compound was conductometrically investigated in different solvents at 120°C. Measurements of the conductivity of the system epoxide-anhydride-tertiary amine as well as that of components and binary solutions indicate that a considerable increase in conductivity appears only in a ternary system. The temporal course of conductivity of the reaction system indicates the ionic character of copolymerization while the conductivity plot shows a maximum. The increase in conductivity in the initial stage of reaction is interpreted as a result of the formation of active centers before reaching a stationary concentration (induction period); the decrease in conductivity is regarded as a consequence of the reduced mobility of macroins due to the increase in molecular weight and macroviscosity of the system and to the dissolving ability of solvent. The absolute value of conductivity of the copolymerization system depends on the polarity of solvent and increases with dielectric constant. Similar results were obtained with the tertiary amine-proton donor catalyst system. The catalytic effect of alkali and ammonium salts brings about rapid dissociation and increase in conductivity of the copolymerization system. AS in catalysis by tertiary amine, the decrease in conductivity is attributed to the decrease in mobility of ions and to a solvent effect. Comparison of maximum conductivities with rate constants for copolymerization points out that the ion pairs of active centers as well as the dissociated salt have a catalytic effect.

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