Thermoresponsive poly(2-oxazoline) surfactants for reversible aggregation and redispersion of polystyrene latexes

Thermoresponsive surfactants offer a versatile route to reversibly control the stability of polymer latexes without the need for permanent surface modification or solid additives. In this work, amphiphilic poly(2-oxazoline)-based surfactants were designed and evaluated as stabilizers for thermoresponsive polystyrene (PS) latexes prepared by emulsion polymerization. Cetyl- and stearyl-terminated poly(2-ethyloxazoline) and poly(2-methyloxazoline) surfactants were synthesized via cationic ring-opening polymerization and characterized by NMR, critical micelle concentration, and LCST measurements. PS latexes stabilized with poly(2-ethyloxazoline) surfactants displayed temperature-triggered aggregation above the LCST and efficient redispersion upon cooling, while poly(2-methyloxazoline)-based systems remained non-responsive. Reversibility was confirmed through repeated heating-cooling cycles using dynamic light scattering and scanning electron microscopy, which showed recovery of particle size and morphology with no detectable fusion or degradation under studied conditions. These results demonstrate that poly(2-oxazoline) surfactants enable reversible, temperature-controlled stabilization of PS latexes through LCST-mediated dehydration of the polymer corona, leading to reduced steric stabilization, providing a simple and additive-free approach to switchable colloidal dispersions.