Precision design for polymethacrylate recycling: a radical ring-opening polymerization approach with systematic degradable thionolactone-centered triads

A recycling by design challenge for methacrylate-rich polymers, with applications such as coatings, casts, protective materials and pharmaceutical formulations, is the precise systematic incorporation of (bio)degradable thioester bonds to achieve intrinsic (bio)degradability upon environmental disposal. Unfortunately the most efficient (degradable) thionolactone dibenzo[c,e]oxepine-5(7h)-thione (DOT) is incompatible with methacrylate derivatives, implying the absence of MMA-DOT-MMA formation in poly(methyl methacrylate (PMMA) backbones. As shown in the present work, DOT can be encapsulated through a fast radical ring-opening polymerization (rROP) in a symmetric triad, by utilizing methyl acrylate (MA) or N-phenyl maleimide (PhMal) as an auxiliary comonomer. The intriguing formation of MA-DOT-MA and PhMal-DOT-PhMal triads is realized, and demonstrated to be compatible with MMA addition. This enables the controlled formation of MMAx-(MA-DOT-MA)-MMAy and MMAx-(PhMal-DOT-PhMal)-MMAy, hence, for the first time the well-defined inclusion of degradable moieties in PMMA backbones with low DOT amounts. Validated Coupled Matrix-based Monte Carlo (CMMC) simulations are utilized to design the synthesis conditions by playing with the initial comonomer and solvent amounts. Specifically, these simulations identified unconventional synthesis conditions, resulting in a 2 times shift in the peak average molar mass for the MMA/DOT/PhMal degradable polymer (number average molar mass Mn of 60,000 g.mol-1) and a 25 times lower Mn for the degraded oligomers (2,000-2,500 g.mol-1 within the target range). The model-based insights have been experimentally confirmed, opening the pathway to regulated (bio)degradability for polymethacrylates under industrially relevant radical polymerization conditions.