Synthesis and thermal behavior of liquid-crystalline block copolymers containing both main-chain and side-chain mesomorphic blocks

A novel type of block copolymers comprising both side-chain and main-chain liquid-crystalline (LC) blocks in the same macromolecular structure was synthesized and studied. The former block was either one of two LC polymethacrylates containing an azobenzene mesogen with different substituents (block A), and the latter was a semiflexible LC polyester block (block B). Thermal, dynamic-mechanical, and X-ray diffraction data indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodynamic phase transition parameters of block A were not affected by copolymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the corresponding homopolymers. In particular, the normalized transition enthalpies of block B were much lower, suggesting the occurrence of a more or less diffuse interphase. An increase in the nematic-isotropic temperature was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component