Hydrogen Atom Transfer-Triggered Chemical Recycling of Commercial Poly(methyl methacrylate) Utilizing Continuous Monomer Removal

A reaction engineering approach combining controlled radical concentration with continuous monomer removal enables efficient depolymerization under practical conditions without light, chlorinated solvents, or high dilution. A semibatch protocol employing multiple small additions of cumene hydroperoxide (CHP) and continuous removal of methyl methacrylate (MMA) suppressed radical side reactions and shifted the equilibrium toward monomer formation.

At a repeating-unit concentration of 1.83 M and a total CHP loading of 3 mol %, depolymerization reached 90% with only 2% monomer consumption. The method remained effective at 3.00 M, scaled to 20 g of polymer (79% depolymerization, 4.5 mol % CHP loading), and was effective for commercial Plexiglas containing stabilizing additives. Recovered MMA was successfully repolymerized, demonstrating its circularity.