EFFECT OF ALPHA-ESTER AND BETA-ESTER ALKYL-GROUPS ON THE PROPAGATION AND TERMINATION RATE CONSTANTS FOR RADICAL POLYMERIZATION OF DIALKYL ITACONATES

Radical polymerizations of seven dialkyl itaconates (DRIs) with methyl, isopropyl, or tert-butyl ester groups were carried out with dimethyl 2,2'-azobis(isobutyrate) in benzene at 60-degrees-C. The effects of the alpha- and beta-ester alkyl substituents (see Chart I) of the DRIs on the polymerization rate (R(p)) and the propagation and termination rate constants (k(p) and k(t)) were examined. For alpha-substitution R(p) decreased with increasing bulkiness of the alkyl group, whereas the opposite was observed for beta-substitution. Electron spin resonance (ESR) spectroscopy revealed that k(p) decreases with bulkiness of the alpha-ester alkyl group in the order methyl > isopropyl > tert-butyl, with little effect observed for substitution at the beta-position, whereas k(t) decreases when bulkier ester alkyl groups are introduced into either the alpha- or beta-position. The dependences of k(p) and k(t) on the structure of the alpha- and beta-ester alkyl groups interpret well the polymerization reactivities of DRI.