PHOTOCHEMICALLY INDUCED ISOTHERMAL PHASE-TRANSITION IN POLYMER LIQUID-CRYSTALS WITH MESOGENIC PHENYL BENZOATE SIDE-CHAINS .2. PHOTOCHEMICALLY INDUCED ISOTHERMAL PHASE-TRANSITION BEHAVIORS

Photochemically induced isothermal phase transition in polymer liquid crystals (PLC) with mesogenic phenyl benzoate side chains has been demonstrated. PLC's examined are poly(4-methoxyphenyl 4-((acryloyloxy)alkoxy)benzoate) (PAPBrc), in which the alkyl spacer length (CH2) was 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(APBn-co-AAZOm) or copolymer n-m). Two types of systems have been explored; one is composed of PAPBn doped with a small amount of a low molecular weight (MW) mesogen with a photoresponsive moiety, 4-butyl-4-methoxyazobenzene (BMAB), and the other is copolymer n-m. Photoirradiation of the PAPB3/BMAB (5 mol%) film at 366-nm light caused the transcis isomerization of BMAB, which induced simultaneously the nematic (N) - isotropic (I) phase transition of the PLC film. This process was reversible, and photoirradiation at 525 nm which induced the cistrans isomerization of BMAB restored the system to the initial phase (N). The phase transition behavior was found to be strongly dependent on the spacer length (n) and MW of the PLC. Similar isothermal phase transition behaviors were observed in copolymer 3-m; however, in other copolymers like copolymer 6-m the isothermal phase transition could not be induced photochemically. Among the PLC samples examined, copolymer 3-3 showed the highest rate of isothermal phase transition. On the basis of the calorimetric studies and order parameter determinations reported in the preceding paper, the efficiency of the photochemically induced isothermal phase transition was found to be closely related to orientational ordering of the initial state of the PLC. Thus, the N-Iisothermal phase transition took place more effectively in a system with a less ordered N state. Resolution of the stored image was estimated as 2-4m on the basis of experiments where copolymer 3-3 was covered with a photomask and irradiated with the third harmonic of a YAG laser. © 1990, American Chemical Society. All rights reserved.