Kinetic analyses were carried out for formation of disulfide crosslinkages between thiol groups on linear polymers, poly(acrylamide-co-N-acrylcysteamine) (P-SH). Disulfide crosslinkages were formed by auto-oxidation of pendant thiol groups or through the thiol-disulfide exchange reaction induced by addition of disulfide compounds gluthathione. In the auto-oxidation reaction, the rate constant for disulfide formation highly depended on pH values of the reaction mixtures and the P-SH concentrations. Gelation rate is too slow to enclose living cells into hydrogel under physiological pH 7.4. The hydrogel formation rate can be accelerated by addition of disulfides, such as oxidized glutathione. In the later case, oxygen in the reaction mixture is not consumed. The thiol-disulfide exchange reaction is much more suitable for the cell encapsulation than the thiol auto-oxidation reaction. These findings give a basis for enclosure of living cells in a hydrogel. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 671-679, 2011