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 tetrahydrofuran (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 the polymers were determined by gel permeation chromatography (GPC). The thermal properties of the polymers such as thermal stability, glass transition temperatures and liquid crystallinity were studied by thermogravimetric analysis, differential thermal analysis, polarizing optical microscopy and X-ray diffractometry. The results show that all the polymers exhibit nematic phases and the increasing of the azo group content broadens the temperature range of the liquid crystalline state. The UV-induced trans/cis photoisomerization and the thermal back-isomerization were also investigated for the azo monomer MAAZO6 and the copolymer P-2 in chloroform. (C) 1998 Elsevier Science Ltd. All rights reserved.