Thermoresponsive hydrogels from ABC triblock terpolymers

We have prepared novel thermoreversible ABC hydrogels from poly(ethylene-alt-propylene)-b-poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEP-PEO-PNIPAm) triblock terpolymers. The terpolymers form micelles in water at low temperatures with hydrophobic PEP cores surrounded by hydrophilic PEO-PNIPAm coronas, and these micelles subsequently associate to form a hydrogel upon heating above the lower critical solution temperature (LCST) of PNIPAm. The separation of micellization and gelation leads to the formation of a two-compartment network with exclusively bridging conformations for the PEO midblocks. Therefore, gelation can be achieved at a much lower concentration, with better mechanical properties and a sharper sol-gel transition, when compared with ABA triblock copolymer hydrogels from PNIPAm-PEO-PNIPAm. The results highlight the intricate nanostructures and new properties available from ABC terpolymer hydrogels.