Poly(N-isopropylacrylamide) nanocrosslinked by polyhedral oligomeric silsesquioxane: temperature-responsive behavior of hydrogels.

Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) was used as a nanocrosslinking agent to prepare the crosslinked poly(N-isopropylacrylamide) (PNIPAM) networks with POSS content up to 50 wt%. The inter-component crosslinking was achieved via the reaction between NH moieties in amide group of PNIPAM and epoxide groups of OpePOSS. When the organic-inorganic nanocomposites were swollen in water the POSS-crosslinked PNIPAM exhibited the characteristics of hydrogels. With the moderate contents of POSS, the POSS-containing hybrid hydrogels displayed much faster response rates in swelling, deswelling and reswelling experiments than the PNIPAM hydrogels prepared via the free radical copolymerization of N-isopropylacrylamide (NIPAM) and N,N(')-methylenebisacrylamide (viz. the conventional crosslinker). The improved hydrogel properties have been interpreted on the basis of the formation of the nanosized hydrophobic microdomains around the POSS moieties (i.e., the nanocrosslinking sites).