Photoresponsive diblock copolymers bearing strong push-pull azo chromophores and cholesteryl groups

A series of diblock copolymers bearing strong push pull azo chromophores and cholesteryl groups on the respective blocks was synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The liquid crystal phase structure, microphase-separated morphology, and photo-responsive properties of the block copolymers were investigated by using DSC, POM, AFM, XRD and laser irradiation. The results show that the cholesteryl block (PChEMA) forms smectic-A mesophase and the morphology depends on the length of the azo block (PAzoCN). When the azo block is short, such as PChEMA(50)-b-PAzoCN(7), no microphase separation can be identified. For PChEMA(50)-b-PAzoCN(28), PAzoCN appears as the hexagonal-packed nanocylinders embedded in the PChEMA matrix. When the azo block length further increases, the block copolymer PChEMA(50)-b-PAzoCN(73) forms microphase-separated lamellae. The microphase separation shows no obvious restraint on the photoinduced orientation of the azo chromophores, but micron-scale mass transport of the photoresponsive PAzoCN block is inhibited by the phase confinement. (C) 2012 Elsevier Ltd. All rights reserved.