LIGHT CONTROLLED SOLUBILITY CHANGE OF POLYMERS - COPOLYMERS OF N,N-DIMETHYLACRYLAMIDE AND 4-PHENYLAZOPHENYL ACRYLATE

Copolymers of N,N-dimethylacrylamide (DMA) and 4-phenylazophenyl acryl ate (PAPA) have been prepared by free-radical copolymerization in diox ane (DMAP-x). The molecular weights of the copolymers show a strong de crease with increasing azobenzene content due to the retardation effec t of the azobenzene group. An analogous decrease in molecular weight w as found with a number of polymers of DMA which were polymerized in th e presence of the non-polymerizable model 4-phenylazophenyl propionate (PAPP). We were able to induce a lower critical solution temperature (LCST) above a certain content of azobenzene moieties in the copolymer s (DMAP-x) in contrast to the good water solubility of poly(DMA). Due to the reversible photoisomerization and the concomitant change in the dipole moment of the azobenzene moieties, the LCST depends not only o n the content of azobenzene but also on the degree of isomerization. A difference in the LCST up to 20-degrees-C was found for dark adapted polymer solutions (0% Z-isomer) and polymer solutions in the photostat ionary state (ca. 85% Z-isomer). Within this temperature range the pol ymer can be precipitated by irradiation with light.