MOLECULAR ADDRESSING - SELECTIVE PHOTOINDUCED COOPERATIVE MOTION OF POLAR ESTER GROUPS IN COPOLYMERS CONTAINING AZOBENZENE GROUPS

Amorphous copolymers with rigid azobenzene and ester side groups form films in which birefringence can be induced using linearly polarized l ight. When both the azobenzene and the ester groups are polar, coopera tive motion occurs and high levels of birefringence can be achieved at relatively low azobenzene content. With less polar ester groups, this cooperative motion is significantly reduced, suggesting that the effe ct is not dictated by steric factors (as is the case in liquid crystal line copolymers), but by electric interaction between the side group d ipoles. The differences in cooperative motion of two copolymer systems : yloyloxy)ethyl)ethyl)ethylamino]-4-nitroazobenzene (DR1M)-co-4-nitro phenyl [(2-methyl-1-oxo-2-propenyl)oxy]ethyl]oxy]benzoate (BEM)} (a po lar azo/polar ester pair), and poly{DR1M-co-4-phenyl -(2-methyl-1-oxo- 2-propenyl)oxy]ethyl]oxy]benzoate (NBEM)} (a polar azo/less polar este r) have been investigated using birefringence measurements and time de pendent infrared spectroscopy. Thus, the ''molecular addressing'' conc ept introduced by Anderle and Wendorff for liquid crystalline copolyme rs is real. Kinetic analysis using time-dependent infrared spectroscop y clearly shows that the azobenzene groups move first and are followed by the ester groups, which move to a much greater degree when they ha ve similar polarity (BEM with DR1M).