Reduction/Oxidation Induced Cleavable/Crosslinkable Temperature-Sensitive Hydrogel Network Containing Disulfide Linkages

Abstract

Temperature-sensitive poly(N-isopropylacrylamide) [poly(NIPPAAm)] was crosslinked with a small amount of N,N'-cystamine-bis-acrylamide which contains a disulfide linkage between two vinyl groups, The hydrogel network could be dissolved into water soluble polymer chains by the reduction of a disulfide bond to two thiol groups. The cleavage of crosslink points led to the experimental determination of the polymer molecular weight (M-n) and the amount of free thiol concentration in the polymer backbone. This permitted the calculation of an average molecular weight between crosslinks (M-e) which has been theoretically predicted by a Flory-Rehner equation based on either swelling or tensile experiments. The experimentally measured. If, values agree well with those obtained from the swelling experiment, When the reduced poly(NIPAAm) was re-oxidized in a dilute aqueous solution, time dependent evolution of inter- and intra-molecularly disulfide linked poly(NIPAAm) species could be observed.