Structure of Two-Compartment Hydrogels from Thermoresponsive ABC Triblock Terpolymers

Aqueous dispersions of a poly(ethylene-alt-propylene)-b-poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PON) triblock terpolymer with block molecular weights of 3 000–25 000–10 000 and polymer concentrations ranging from 1 to 5 wt % were investigated at several temperatures from 25 to 55 °C using cryogenic scanning electron microscopy (cryo-SEM), cryogenic transmission electron microscopy (cryo-TEM), and small-angle neutron scattering (SANS). The cryo-SEM and cryo-TEM micrographs revealed that PON triblock terpolymer self-assembled into spherical micelles with PEP cores and PEO–PNIPAm coronae at room temperature and subsequently formed a two-compartment micellar network consisting of distinct spherical PEP and PNIPAm cores upon heating above the critical gelation temperature (42 °C). The formation of two discrete spherical PEP and PNIPAm hydrophobic domains was supported by detailed SANS analysis of the PON triblock samples in D2O, as the resulting intensity profiles can be successfully fitted using a...