Surfactant-Free Visible-Light-Controlled Emulsion Polymerization Toward Aba-Type Amphiphilic Triblock Copolymers

Surfactant-free visible-light-controlled emulsion polymerizations are demonstrated here to synthesize ABA-type amphiphilic triblock copolymers, where A represents the hydrophilic block of poly(acrylic acid) (PAA) and B represents the hydrophobic block, such as poly(butyl acrylate) (PBA), poly(ethyl acrylate) (PEA), poly(trifluoroethyl acrylate) (PTFEA), and poly(hexafluorobutyl acrylate) (PHFBA). The photoiniferter solution polymerization of acrylic acid (AA) in 1,4-dioxane was first performed under air atmosphere and successfully controlled by visible light with the existence of iniferter agent and ascorbic acid. Using the as-synthesized PAA with trithioester end-groups as macro-iniferter agent, ABA-type triblock copolymers were synthesized in an aqueous emulsion system. Chain growth of various hydrophobic B blocks induced self-assembly and micellization. The micelles were in turn swelled by monomers and acted as main reaction loci for the further photoiniferter emulsion polymerizations. All the polymerizations showed typical characteristics of controlled/living radical polymerization (CLRP) and an obvious "on and off" feature controlled by visible light. Compared with solution polymerizations, emulsion polymerizations exhibited higher polymerization rate and monomer conversion, and an ability to directly produce colloidal polymer microparticles.