PHOTOREACTIVITY OF POLYMERS WITH REGIOISOMERIC CINNAMATE SIDE-CHAINS AND THEIR ABILITY TO REGULATE LIQUID-CRYSTAL ALIGNMENT

Photoproduct distribution in films of cinnamate polymers was analyzed to reveal the contribution of both photoisomerization and photodimeriz ation to LC alignment photoregulation. A polymethacrylate with o-cinna mate side chains displayed preferential formation of Z-isomer while th e dimerization takes place more favorably for other polymers including poly(vinyl cinnamate). On the basis of the relationship between photo product distribution and liquid crystal photoalignment and on the reve rsibility of the photoinduced reorientation of a liquid crystal, it wa s concluded that the photoalignment results from the polarization phot oisomerization of cinnamate residues in the same manner as that of pho tochromic moieties like azobenzenes, whereas the (2 + 2) photodimeriza tion plays a role in enhancing the thermal stability of the homogeneou s photoalignment.