SYNTHESIS, THERMAL CHARACTERIZATION AND RHEOLOGICAL PROPERTIES OF A HOMOLOGOUS SERIES OF POLYMETHACRYLATE-BASED SIDE-CHAIN LIQUID-CRYSTAL POLYMERS

A new homologous series of side-chain liquid crystal polymers, the pol y[omega-(4-cyanoazobenzene-4'-oxy)alkyl methacrylate]s, have been prep ared in which the length of the flexible alkyl spacer is varied from 3 to 12 methylene units. All the polymers exhibit liquid crystalline be haviour; specifically, crystal E, smectic A and nematic phases are obs erved. The glass transition temperatures decrease on increasing spacer length before reaching a limiting value at ca. 30 degrees C. The clea ring temperatures exhibit an odd-even effect on varying the length and parity of the spacer. This is attributed to the change in the average shape of the side chain as the parity of the spacer is varied. This r ationalization also accounts for the observed alternation in the entro py change associated with the clearing transition. A weak relaxation i s observed theologically for several members of this polymer series at temperatures above their respective glass transition temperatures. Th is is attributed either to specific motions of the smectic layers or t o 180 degrees reorientational jumps of the long axis of the mesogenic unit about the polymer backbone. (C) 1997 Elsevier Science Ltd. All ri ghts reserved.