Stimuli-responsive diblock copolymer brushes via combination of "click chemistry" and living radical polymerization

Abstract

pH- and temperature-responsive poly(N-isopropylacrylamide-block4-vinylbenzoic acid) (poly(NIPAAm-b-VBA)) diblock copolymer brushes on silicon wafers have been successfully prepared by combining click reaction, single-electron transfer-living radical polymerization (SET-LRP), and reversible addition-fragmentation chain-transfer (RAFT) polymerization. Azide-terminated poly(NIPAAm) brushes were obtained by SET-LRP followed by reaction with sodium azide. A click reaction was utilized to exchange the azide end group of a poly(NIPAAm) brushes to form a surface-immobilized macro-RAFT agent, which was successfully chain extended via RAFT polymerization to produce poly(NIPAAm-b-VBA) brushes. The addition of sacrificial initiator and/or chain-transfer agent permitted the formation of well-defined diblock copolymer brushes and free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. Ellipsometry, contact angle measurements, grazing angle-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the immobilization of initiator on the silicon wafer, poly(NIPAAm) brush formation via SET-LRP, click reaction, and poly(NIPAAm-b-VBA) brush formation via RAFT polymerization. The poly(NIPAAm-b-VBA) brushes demonstrate stimuli-responsive behavior with respect to pH and temperature. The swollen brush thickness of poly(NIPAAm-b-VBA) brush increases with increasing pH, and decreases with increasing temperature. These results can provide guidance for the design of smart materials based on copolymer brushes. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 26772685