Thermoreversible physically crosslinked hydrogels from UCST-type thermosensitive ABA linear triblock copolymers†
This article reports on a new class of thermoreversible physically crosslinked hydrogels formed from ABA linear triblock copolymers composed of a hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMMA) middle block and UCST-type thermosensitive poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) outer blocks. A series of P(AAm-co-AN)-b-PPEGMMA-b-P(AAm-co-AN) ABA triblock copolymers was prepared by reversible addition–fragmentation chain transfer polymerization using a difunctional chain transfer agent. At appropriate block lengths, chemical compositions, and polymer concentration, aqueous solutions of the ABA triblock copolymers underwent cooling-induced, reversible sol–gel transitions in water, and the sol–gel transition temperature increased with the increase of the outer block length, the AN molar content in the outer block, and polymer concentration. Dynamic light scattering studies confirmed that the cooling-induced sol–gel transition stemmed from the UCST behavior of the outer blocks of ABA triblock copolymers. These UCST-type thermosensitive block copolymer hydrogels expanded the scope of injectable polymer hydrogels, and will have potential applications in many areas.