Preparation, characterization and novel photoregulated rheological properties of azobenzene functionalized cellulose derivatives and their at-CD complexes

Novel azobenzene functionalized hydroxypropyl methylcellulose (AZO-HPMC) polymers and their alpha-CD (alpha-Cyclodextrin) complexes have been prepared. FT-IR, H-1 NMR and FT-Raman spectroscopy confirm the existence of azobenzene chromophores in AZO-HPMC polymers. alpha-CD can improve the water solubility of AZO-HPMC by formation of inclusion complexes with azobenzene side groups. Rheological studies substantiate that both AZO-HPMC and its alpha-CD complex undergo thermoreversible sol-gel transitions, in aqueous solutions. Viscometric measurements suggest that the association between azobenzene side groups can be eliminated by a-CD. The effect of photoirradiation on the rheological behavior shows that the gelation temperature of AZO-HPMC increases after UV irradiation, while the gelation temperature of AZO-HPMC/alpha-CD complex decreases after UV irradiation. (C) 2004 Elsevier Ltd. All rights reserved.