Synthesis of 4-acetoxystyrene – t-butyl acrylate statistical, block and gradient copolymers, and the effect of the structure of copolymers on their properties

Abstract

The properties of copolymers are affected greatly by the composition as well as the chain structure of the copolymers. Consequently, gradient copolymers, due to the uniqueness of their structures show significantly different properties than those of the conventional statistical and block copolymers. This study reports the synthesis of 4-acetoxystyrene – t-butyl acrylate (AOST-tBA) statistical copolymers by reversible addition-fragmentation chain-transfer (RAFT) and free radical polymerization (FRP) methods, and also the synthesis of block and gradient copolymers of AOST-tBA by the RAFT method. The gradient structure in the AOST-tBA copolymer was produced by continuously adding a second monomer to the polymerization system to taper the copolymer composition. Differential scanning calorimetry (DSC) analysis found a broad transition for the gradient copolymer, in contrast to a single narrow transition for the statistical copolymer and two narrow transitions for the block copolymer. The acetoxy groups from the AOST-tBA copolymers were de-acetylated to convert the AOST to hydroxystyrene (HOST). Fourier transform infra-red (FTIR) studies revealed that the extent of hydrogen bonding in thin films of the HOST-tBA copolymers is greatly influenced by the copolymer composition as well as the chain structure. However, no significant differences were found for the surface compositions and surface free energies of copolymers. The properties of HOST-tBA copolymers synthesized by RAFT and FRP have also been compared in this study.