Photo-Initiated Main-Chain Scission of Poly(methyl methacrylate) in Solution at Room Temperature

Poly(methyl methacrylate) (PMMA), as a widely used transparent polymer material, is highly stable because of its all-carbon backbone, which makes its chain cleavage under mild conditions challenging. In this work, we report a photo-initiated solution reaction that induces main-chain scission of PMMA at room temperature, leading mainly to molecular-weight reduction and oligomer formation. This method requires no catalysts and does not need pre-introduction of specific groups. The degradation mechanism proposed according to DFT calculations involves the photolysis of trichloromethane to produce phosgene, which then reacts with ester groups on the side chains of PMMA to form acyl chloride groups. These acyl chloride groups further cleave under light or heat, generating radicals that trigger β-scission of the PMMA main chain through a side-chain-initiated pathway. The degradation mechanism was demonstrated experimentally, and the extent of chain scission can be regulated by temperature, O₂ and an alcohol stabilizer.