Block Copolymers of γ-Methacryloxypropyltrimethoxysilane and Methyl Methacrylate by RAFT Polymerization. A New Class of Polymeric Precursors for the Sol−Gel Process

Abstract

Reversible addition−fragmentation chain transfer (RAFT) polymerization of the reactive monomer γ-methacryloxypropyltrimethoxysilane (γMPS) mediated by 2-cyanoprop-2-yl dithiobenzoate (CPDB) has been studied in dioxane using 2,2‘-azobis(isobutyronitrile) (AIBN) as initiator. Conditions were optimized for a polymerization temperature of 80 °C, and controlled PγMPS chains (up to Mn = 40 000 g mol-1) exhibiting low polydispersity indexes (PDI < 1.3) were synthesized. Their characterization by matrix-assisted laser desorption ionization time-of-flight (MALDI-ToF) mass spectrometry showed that the expected structure was obtained although degradation of the dithiobenzoate chain end occurred. Syntheses of block copolymers based on γMPS and methyl methacrylate (MMA) were performed starting from either the PγMPS (Mn = 32 100 g mol-1, PDI = 1.16, PMMA calibration) or the PMMA block (Mn = 21 000 g mol-1, PDI = 1.14). The success of the block copolymerization was showed by the shift toward higher molar mass of the size exclusion chromatography (SEC) chromatograms recorded before and after block copolymerization. Proton NMR analyses of P(MMA-b-γMPS) allowed to calculate the molar mass of the PγMPS blocks (17 400 g mol-1) which agreed with the targeted one (18 150 g mol-1).