Thermoresponsive Gelation and Phase Transition of PEG/Cation Random Terpolymer Micelles in Water in the Presence of Salts

This is the authors' abstract. We don't add key points for this paper.

Amphiphilic random terpolymers bearing hydrophilic poly(ethylene glycol) (PEG) chains, quaternary ammonium cations, and hydrophobic dodecyl groups form size-controlled micelles in water. The terpolymer micelles show a lower critical solution temperature (LCST)-type solubility in water in the presence of salts. Focusing on the features, we herein investigated the thermoresponsive properties of the concentrated aqueous solutions of the PEG/cation random terpolymer micelles containing NaCl to find unique gelation and phase transition dependent on the PEG/cation composition. Upon heating, the PEG/cation (2/1, 1/1, and 1/2) terpolymer micelle solutions exhibited a two-step phase transition through transient gelation to viscous and turbid solutions via LCST-type phase separation. In contrast, a cation-rich PEG/cation (1/3) terpolymer micelle and a cation copolymer micelle formed gels in water at room temperature, where the former changed to a viscous and transparent solution upon heating. The rheological properties of the gels can be tuned by the PEG/cation ratio and degree of polymerization of the terpolymers. Small-angle neutron scattering measurements revealed that the transient gelation of the terpolymer micelle solutions occurred via the formation of intermicellar networks.