Photochemical and Thermal Isomerizations of Azobenzene-Containing Amphiphilic Diblock Copolymers in Aqueous Micellar Aggregates and in Film

Homopolymers of azobenzene methacrylates (azo) and their diblock copolymers with 2-(dimethylamino)ethyl metharylate (DMAEMA) were synthesized via atom transfer radical polymerization (ATRP). Polymers of cyano- and butoxy-substituted azobenzenes exhibited liquid crystalline textures. Water-soluble diblock copolymers could be obtained with a long DMAEMA block and a short azo block. These diblock copolymers self-assembled into polymeric micelles with core−shell structure in aqueous solutions. The rates of trans−cis photoisomerization were almost the same for the DMAEMA copolymers of 6-[4-phenylazo]phenoxy]hexyl methacrylate (PPHM), p(DMAEMA172-b-PPHM9), and 6-[4-(4-cyanophenylazo)phenoxy]hexyl methacrylate (CPHM), p(DMAEMA172-b-CPHM7), whereas slightly slower rates were observed for the copolymer of 6-[4-(4-butoxyphenylazo)phenoxy]hexyl methacrylate (BPHM), p(DMAEMA172-b-BPHM7), most likely due to steric hindrance presented by the bulky butoxy group. The rates in aqueous micellar solutions were only marginal...