K. Ichimura et al., PHOTOREACTIVITY OF POLYMERS WITH REGIOISOMERIC CINNAMATE SIDE-CHAINS AND THEIR ABILITY TO REGULATE LIQUID-CRYSTAL ALIGNMENT, Macromolecules, 30(4), 1997, pp. 903-911
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.