Miniemulsion Ring-Opening Radical Polymerization with Dibenzo[<i>c</i>,<i>e</i>]oxepan-5-thione for Degradable Polymer Particles

Polymer-based particulate materials are useful in various industries, but nondegradable polymeric particulate materials that generate microplastics pose challenges. Herein, we synthesized main-chain degradable polymer particles by radical ring-opening polymerization (rROP) in a miniemulsion system (miniemulsion rROP), in which dibenzo[c,e]oxepan-5-thione (DOT) was selected as the ring-opening monomer. Miniemulsion rROP of DOT and typical vinyl comonomers (styrene: St and n-butyl acrylate: nBA) was performed. The polymerization rate of the miniemulsion rROP was significantly higher than that of solution rROP. The DOT feed molar ratio in the miniemulsion rROP was increased to 20 mol % with high conversion. Colloidally stable poly(St-DOT) particles were successfully synthesized and were degraded by amine compounds in homogeneous and heterogeneously dispersed systems. Additionally, when nBA was used as the vinyl monomer, colloidally stable main-chain degradable poly(nBA-DOT) particles were successfully synthesized, and their degradation was observed with n-propylamine, evidencing the possibility of using miniemulsion rROP to synthesize degradable polymer particles.