Diverse approaches to star polymers via cationic and radical RAFT cross-linking reactions using mechanistic transformation

Abstract

Core cross-linked star polymers were successfully synthesized via cationic reversible addition fragmentation chain-transfer (RAFT) polymerization, which produces macro RAFT agents as the arm polymers, followed by three different approaches used for the block copolymerization of divinyl monomers as the core and subsequent cross-linking reaction. The following three approaches were used: (i) one-pot cationic RAFT block polymerization and the simultaneous cross-linking reaction of divinyl ether; (ii) mechanistic transformation to radical RAFT block polymerization and the simultaneous cross-linking reaction of a hetero divinyl monomer, which possesses both vinyl ether and acrylate moieties; and (iii) one-pot cationic RAFT selective block copolymerization of the vinyl ether moiety in the hetero divinyl monomer, followed by mechanistic transformation to a radical cross-linking reaction of the acrylate moiety that remained in the pendant groups of the diblock polymer. All three methods were free from metal catalysts and produced core cross-linked star polymers with controlled molecular weights (M_w = 2–6 × 10⁵), narrow molecular weight distributions (M_w/M_n = 1.1–1.4), and controlled arm numbers (N_arm = 15–40) and sizes (D_n = 18–28 nm, D_w/D_n = 1.03–1.06) in relatively high yields (80–94%).