Core cross-linked star (CCS) polymers with tunable polarity: synthesis by RAFT dispersion polymerization, self-assembly and emulsification

Abstract

Homoarm and heteroarm core cross-linked star (CCS) polymers based on poly(N,N-dimethylacrylamide) (PDMA) as the high-polarity arm and poly(2-methoxyethylacrylate) (PMEA) as the low-polarity arm were efficiently prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization in a dispersion polymerization system. PDMA and PMEA arm polymers exhibited similar conversion rates, such that their composition in the heteroarm CCS polymers was easily controlled by the feed ratio in the synthesis. The ability to control the arm composition allowed facile tuning of the polarity of the CCS polymers. Heteroarm CCS polymers self-assembled in water to form aggregates and their size was related to the composition and polarity of the CCS polymers. The composition and polarity of the CCS polymers significantly affected the emulsifying behaviour of the CCS polymers as emulsifiers. Oil-in-water (o/w) emulsions were favoured for CCS polymers with relatively high polarity and lowering the polarity of CCS polymers to a certain degree enhanced the stability of the emulsions. Multiple emulsions, both o/w and water-in-oil (w/o), were gradually produced when the polarity of CCS polymers was gradually lowered and the oil fraction in the emulsion samples was gradually increased, and at the same time the emulsions also became increasingly less stable.