Depolymerization of poly(α-methyl styrene) with ball-mill grinding

The development of mild methods to depolymerize polymers has become increasingly important in our current Age of Plastics, and ball-mill grinding (BMG) is emerging as a promising candidate. In this report, we demonstrate that subjecting poly(alpha-methyl styrene) (PMS) to BMG leads to high extents of depolymerization (up to 64 mol% of alpha-methyl styrene was produced) with minimal side products after only minutes of grinding. Constrained geometries simulate external force (CoGEF) simulations and radical trapping experiments supported that the depolymerization was initiated by mechanochemical chain scission. Depolymerization proceeded despite bulk temperatures remaining far below that of the ceiling temperature of PMS. Control experiments suggested that the extent of depolymerization was equilibrium controlled. Polystyrene and poly(methyl methacrylate) also underwent depolymerization, although to a much lesser degree (up to 4% monomer produced), presumably due to their much higher ceiling temperatures. This work provides an entry point for further development of BMG as a tool for the depolymerization of vinyl polymers under mild conditions.

Automated summary

In this study, ball-mill grinding (BMG) was found to effectively depolymerize poly(alpha-methyl styrene) (PMS) with minimal side products. Mechanochemical chain scission was identified as the mechanism for the depolymerization, which was supported by constrained geometries simulate external force (CoGEF) simulations and radical trapping experiments. The depolymerization proceeded even at temperatures below the ceiling temperature of PMS. This research provides a starting point for further development of BMG as a mild method for depolymerizing vinyl polymers.