Organic-inorganic hybrid hydrogels involving poly(N-isopropylacrylamide) and polyhedral oligomeric silsesquioxane: Preparation and rapid thermoresponsive properties

Abstract

3-Acryloxypropylhepta(3,3,3-trifluoropropyl) polyhedral oligomeric silsesquioxane (POSS) was synthesized and used as a modifier to improve the thermal response rates of poly(N-isopropylacrylamide) (PNIPAM) hydrogel. The radical copolymerization among N-isopropylacrylamide (NIPAM), the POSS macromer and N,N0-methylenebisacrylamide was performed to prepare the POSS-containing PNIPAM cross-linked networks. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) showed that the POSS-containing PNIPAM networks displayed the enhanced glass transition temperatures (Tg's) and improved thermal stability when compared with plain PNIPAM network. The POSS-containing PNIPAM hydrogels exhibited temperature-responsive behavior as the plain PNIPAM hydrogels. It is noted that with the moderate contents of POSS, the POSS-containing PNIPAM hydrogels displayed much faster response rates in terms of swelling, deswelling, and re-swelling experiments than plain PNIPAM hydrogel. The improved thermoresponsive properties of hydrogels have been interpreted on the basis of the formation of the specific microphase-separated morphology in the hydrogels, that is, the POSS structural units in the hybrid hydrogels were self-assembled into the highly hydrophobic nanodomains, which behave as the microporogens and promote the contact of PNIPAM chains and water. © 2009 Wiley Periodicals, Inc.