Surfactant-free poly(vinylidene chloride) latexes via one-pot RAFT-mediated aqueous polymerization

Abstract

Water-soluble polymers obtained by reversible addition-fragmentation chain transfer (RAFT) polymerization were used for the production of surfactant-free poly(vinylidene chloride) (PVDC)-based latexes in a one-pot/two-step process that was exclusively conducted in water. In the first step, the hydrophilic macromolecular RAFT (macroRAFT) agent (i.e. poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA) or poly(sodium 4-styrenesulfonate) (PSSNa)) was synthesized in water using a trithiocarbonate RAFT agent, 4-cyano-4-thiothiopropylsulfanyl pentanoic acid (CTPPA). The macroRAFT agent was then directly utilized as reactive stabilizer for the aqueous emulsion copolymerization of vinylidene chloride (VDC) and methyl acrylate (MA) inspired by a polymerization-induced self-assembly (PISA) process. The developed recipes employed a very low amount of macroRAFT agent compared to the hydrophobic monomers (typically less than 2 wt%) and amphiphilic block copolymers of PAA-b-P(VDC-co-MA), PMAA-b-P(VDC-co-MA) or PSSNa-b-P(VDC-co-MA) were thus produced in situ, providing stabilization to the P(VDC-co-MA) particles. Stable, surfactant-free latexes were successfully obtained in each case with solids content up to 40 wt%. Surface tension measurements performed on the final dispersions showed that the amount of residual macroRAFT agent in water was negligible demonstrating that this strategy indeed gave rise to particles stabilized by covalently-anchored hydrophilic polymers. The PSSNa macroRAFT agents proved to be particularly interesting candidates achieving stable latexes of less than 100 nm leading to the formation of transparent films which did not whiten after being immersed in water.