High density cationic polymer brushes from combined "click chemistry" and RAFT-mediated polymerization

Abstract

A simple method for preparing cationic poly[(ar-vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was used by combined technology of click chemistry and reversible addition-fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agent by using a click reaction involving an azide-modified silicon wafer and alkyne-terminated 4-cyanopentanoic acid dithiobenzoate (CPAD). A series of poly(VBTAC) brushes on silicon surface with different molecular weights, thicknesses, and grafting densities were then synthesized by RAFT-mediated polymerization from the surface immobilized CPAD. The immobilization of CPAD on the silicon wafer and the subsequent polymer formation were characterized by X-ray photoelectron spectroscopy, water contact angle measurements, grazing angle-Fourier transform infrared spectroscopy, atomic force microscopy, and ellipsometry analysis. The addition of free CPAD was required for the formation of well-defined polymer brushes, which subsequently resulted in the presence of 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. In addition, by varying the polymerization time, we were able to obtain poly(VBTAC) brushes with grafting density up to 0.78 chains/nm2 with homogeneous distributions of apparent needle-like structures. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012