SYNTHESIS AND THERMAL-BEHAVIOR OF LIQUID-CRYSTALLINE BLOCK-COPOLYMERSCONTAINING BOTH MAIN-CHAIN AND SIDE-CHAIN MESOMORPHIC BLOCKS

A novel type of block copolymers comprising both side-chain and main-c hain liquid-crystalline (LC) blocks in the same macromolecular structu re 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 d ata indicated that the two structurally different blocks were at least partly phase-separated within the glassy and LC states. The thermodyn amic phase transition parameters of block A were not affected by copol ymer composition. However, significant deviations of the thermodynamic parameters of block B were observed relative to those of the correspo nding homopolymers. In particular, the normalized transition enthalpie s of block B were much lower, suggesting the occurrence of a more or l ess diffuse interphase. An increase in the nematic-isotropic temperatu re was found at variance with previous results on most of the LC block copolymers, in which only one block was an LC component.