PHOTOCHEMICALLY INDUCED ISOTHERMAL PHASE-TRANSITION IN POLYMER LIQUID-CRYSTALS WITH MESOGENIC PHENYL BENZOATE SIDE-CHAINS .1. CALORIMETRIC STUDIES AND ORDER PARAMETERS

In order to explore photochemically induced isothermal phase transition behaviors of polymer liquid crystals (PLC) with mesogenic phenyl benzoate side chains in relation to their morphological properties, orientational ordering of the PLC's was studied by means of calorimetric measurements and order parameter (S) determinations by FT-IR dichroism. The PLC samples studied are poly(4-methoxy-phenyl 4-((acryloyloxy)alkoxy)benzoate) (PAPBn) in which the alkyl spacer length (CH2)nwas varied as n = 2, 3, 5, or 6 and their copolymers with 4-methoxy-4-((acryloyloxy)alkoxy)azobenzene (AAZOm) where m = 2, 3, 5, 6, or 11 (poly(APBrc-co-AAZOm) or copolymer n-m). Calorimetric studies revealed that PAPB3 exhibited particularly low values of Tm (nematic to isotropic phase transition temperature), ΔSNI(enthalpy change at N-I transition), and ASni (entropy change at N-I transition). Furthermore, these quantities were strongly dependent on molecular weight (MW) and spacer length (n). In copolymer n-m, copolymer 3-3 possessed the lowest values of ΔHNIand ΔSNI, which were even lower than those of PAPB3. IR dich-roic studies have shown a parallel relationship between ΔSNIand S. Namely, among the homopolymers, PAPB3 showed the smallest S and among the copolymers copolymer 3-3 possessed the smallest S. The S value of copolymer 3-3 was further lower than that of PAPB3, indicating that copolymer 3-3 has the least orientational ordering in the N state among the PLC samples examined. © 1990, American Chemical Society. All rights reserved.