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

Abstract We report a thermal hydrogen atom transfer (HAT) depolymerization strategy for the efficient chemical recycling of unmodified commercial poly(methyl methacrylate) (PMMA). 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. These results establish radical concentration control and continuous monomer removal as the key design principles for hydroperoxide-assisted thermal HAT depolymerization.