Synthesis and characterization of new liquid-crystalline block copolymers with p-cyanoazobenzene moieties and poly(n-butyl acrylate) segments using atom-transfer radical polymerization

Homopolymers with side-chain liquid-crystalline units (LC) were prepared by ATRP of a LC monomer, 2- [2-(4-cyano-azobenzene-4'-oxy)ethylene-oxy] ethyl methacrylate. The resulting polymers had low polydispersity, M-w/M-n < 1.2. Optical and thermal investigation confirmed that both the monomer and the homopolymers have smectic structures. New di- and triblock copolymers containing LC units, with different ratios of the block containing the LC monomer with azobenzene moiety, and poly(n-butyl acrylate) as a soft segment were successfully prepared using ATRP. The block copolymerization proceeded with controlled/living characteristics. The morphologies of thin films of the block copolymers cast from different solvents were examined by atomic force microscopy using different casting procedures. Whereas the observed morphologies were similar to those observed in conventional block copolymers, particularly strong dependence on sample preparation conditions and thermal history was observed, suggesting the role of mesogenic blocks in stabilization of metastable states.