Characterization of unidirectional photopolymerization in poly(vinyl cinnamate) by surface optical second-harmonic generation

Surface optical second-harmonic generation measurements were used to determ ine the change in the surface density and the surface orientational order p arameter of the trans-cinnamoyl side groups of unidirectionally photopolyme rized poly(vinyl cinnamate) (PVCN) films. The observed surface features wer e compared to the bulk properties of the films, which were probed by their UV absorption spectra and birefringence measurements. We found that the sur face and the bulk photoreaction kinetics of the trans cinnamoyl side groups of the PVCN are very similar. The two photoreaction processes (trans-cis p hotoisomerization and photo-induced cross linking) appear to affect the lin ear and nonlinear optical properties of the polymer differently. This may e xplain the discrepancy between the birefringence and the azimuthal anchorin g force of the unidirectionally photopolymerized PVCN. [S1063-651X(99)06909 -3].