Characterization of photo- and thermoresponsible amphiphilic copolymers having azobenzene moieties as side groups

Two series of amphiphilic copolymers, poly(HPMA-co-MPAP) I-V with n = 0.05-0.29 of the molar ratio of MPAP and poly(HPMA-co-MPAH)-I-V with n = 0.05-0.23 of the molar ratio of MPAH, were prepared by radical copolymerization of N-(2-hydroxypropyl) methacrylamide (HPMA) with azo-monomers such as 4-(4-methoxyphenylazo) phenyl methacrylate (MPAP) and 6- [4-(4-methoxyphenylazo) phenoxy] hexyl methacrylate (MPAH) using 2,2 ' -azobisisobutyronitrile as an initiator. Self-organization of these copolymers in water was confirmed by disappearance of the proton signal of the methoxyazobenzene in H-1-NMR spectra measured in the solvent system of D2O and CD3OD. It was also found from the lambda (max), located near 344 nm, that azobenzene groups self-organized to form the dimeric chromophore type of aggregate. The aqueous solutions of poly(HPMA-co-MPAP) and poly(HPMA-co-MPAH) exhibited the lower critical solution temperature (LCST) from at 68 to 40 degreesC and from at 70 to 52 degreesC in the dark state, respectively, with increasing the molar ratios of azo-monomers. On the other hand, the LCST measured in the photostationary state showed the higher temperature by 2-4 degreesC compared with that in the dark state. It was found that the adsorption of poly(HPMA-co-MPAP)-V (n = 0.29) on polystyrene microspheres was photoregulated. (C) 2001 John Wiley & Sons, Inc.