New poly(ethylene oxide)-based block copolymers (ssBCs) with a random copolymer block consisting of a reduction-responsive disulfide-labeled methacrylate (HMssEt) and a thermoresponsive di(ethylene glycol)-containing methacrylate (MEO2MA) units were synthesized. The ratio of HMssEt/MEO2MA units in the random P(MEO2MA-co-HMssEt) copolymer block enables the characteristics of well-defined ssBCs to be amphiphilic or thermoresponsive and double hydrophilic. Their amphiphilicity or temperature-induced self-assembly results in nanoaggregates with hydrophobic cores having different densities of pendant disulfide linkages. The effect of disulfide crosslinking density on morphological variation of disulfide-crosslinked nanogels is investigated. In response to reductive reactions, the partial cleavage of pendant disulfide linkages in the hydrophobic cores converts the physically associated aggregates to disulfide-crosslinked nanogels. The occurrence of in-situ disulfide crosslinks provides colloidal stability upon dilution. (c) 2014 Wiley Periodicals, Inc.