Tailor-made compositional gradient copolymer by a many-shot RAFT emulsion polymerization method

Abstract

A many-shot RAFT emulsion polymerization method is proposed to synthesize gradient copolymers with high molecular weight and a tailor-made compositional gradient. In this method each shot consisting of comonomers with pre-set different fractions and targeting the molecular weight of 10 000 g mol⁻¹ was added in a stepwise manner during the reaction. High conversions over 95% were achieved in 35 min after each shot. The compositional variation along the polymer chain was then directly determined by the comonomer fractions added at each shot. Styrene/n-butyl acrylate gradient copolymers (including linear and V-shaped gradient) with molecular weights as high as 90 000 g mol⁻¹ were prepared by this method. The composition profiles along the polymer chains agreed well with the theoretical predictions, and the composition distribution among the polymer chains was narrow. The gradient copolymers showed different thermal and phase separation properties from their block counterparts, as expected. These results demonstrated the successful tailor-making of the gradient copolymers. The current strategy will act as a facile method to prepare tailor-made gradient copolymers with high molecular weights and within a short time.