Reactive triblock copolymer micelles induced by click reaction: A platform for RAFT polymerization

Abstract

In this manuscript in situRAFT polymerization inside reactive triblock copolymer micelles were reported. Poly(ethylene glycol)-block-poly(2-hydroxyethyl methacrylate)-block-poly(tert-butyl acrylate) (PEG-b-PHEMA-b-PtBA) triblock copolymer was synthesized through two-step ATRP of HEMA and tBA by using ATRP initiator terminated PEG as macroinitiator. The pendant azide groups were introduced to the short mid-blocks by reactions of the triblock copolymer with 2-bromoisobutyryl bromide and sodium azide, respectively. Click reaction between the azido-modified triblock and dialkynetrithiocarbonate results in the formation of the reactive micelles with cross-linked cores and PtBA/PEG coronae. The size of the micellar aggregates is determined by initial polymer concentration. The entrapped reversible addition-fragmentation chain transfer (RAFT) agent molecules in the cores were used in RAFT polymerization of N-isopropylacrylamide (NIPAM). After RAFT polymerization, polymeric micelles with cross-linked PNIPAM cores and PEG/PtBA coronae were obtained. FTIR, 1H NMR, dynamic light scattering and transmission electron microscopy were used to characterize the structures of the micelles before and after RAFT polymerization. The degradation of the micelles was also investigated in this research. This type of micelles can be used as a platform for RAFT polymerization.