Free-Radical Modification of Polypropylene. I. Grafting of Poly(Ethyl Acrylate) on Atactic Polypropylene

Abstract

The synthesis of atactic poly(propylene-g-ethyl acrylates) of [Mbar]_n ∼ 3000–5000 has been accomplished with 80–90% incorporation of the backbone in the graft copolymer. The principle involves free radical initiation of ethyl acrylate polymerization with benzoyl peroxide via chain transfer. At low conversions (up to ∼15%), massive homopolymerization took place and the initial rates of both homo- and graft copolymerizations were indistinguishable even with 1% initiator based on monomer. Grafting occurred at higher conversions and the [Mbar]_n of the grafted product increased with increasing initiator concentration for almost similar conversion data. The isothermal stability of the graft copolymer was far superior to that of atactic polypropylene. The initial decomposition temperature of the graft copolymers increased with increasing initiator amount used for grafting. It is proposed that the number of branches of poly (ethyl acrylate) increased, following the abstraction of an increasing number of tertiary hydrogen atoms from the backbone.