SYNTHESIS AND CHARACTERIZATION OF NOVEL PHOTOCHROMIC SIDE-CHAIN LIQUID-CRYSTALLINE POLYMETHACRYLATES CONTAINING PARA-NITROAZOBENZENE GROUP

Methacrylate monomers containing a mesogenic group and a photochromic para-nitroazobenzene group were prepared and polymerized in tetrahydro furan (THF) using 2,2'-azobis(isobutyronitrile) (AIBN) as initiator at 67 degrees C. The polymers were characterized by H-1 NMR, IR, UV-Vis spectra and elemental analyses. The molecular weights M-w and M-n of t he polymers were determined by gel permeation chromatography (GPC). Th e thermal properties of the polymers such as thermal stability, glass transition temperatures and liquid crystallinity were studied by therm ogravimetric analysis, differential thermal analysis, polarizing optic al microscopy and X-ray diffractometry. The results show that all the polymers exhibit nematic phases and the increasing of the azo group co ntent broadens the temperature range of the liquid crystalline state. The UV-induced trans/cis photoisomerization and the thermal back-isome rization were also investigated for the azo monomer MAAZO6 and the cop olymer P-2 in chloroform. (C) 1998 Elsevier Science Ltd. All rights re served.