Full atom-efficiency transformation of wasted polycarbonates into epoxy thermosets and the catalyst-free degradation of the thermosets for environmental sustainability

We report two sustainable features in this work. The first feature is that we successfully applied wasted polycarbonate (WPC) as an epoxy curing agent for epoxy resins to prepare WPC-cured epoxy thermosets. The curing of WPC and epoxy is based on the reaction of a carbonate and an epoxide, which is proven by a model reaction of diphenyl carbonate (DPC) and glycidyl phenyl ether (GPE) in the presence of a catalytic amount of 4-dimethylaminopyridine (DMAP). The WPC-cured epoxy thermosets show comparable thermal properties to commercial-based, phenol novolac (PN)-cured epoxy thermosets. Interestingly, the films of WPC-cured epoxy thermosets are foldable, while those of PN-cured epoxy thermosets are brittle, demonstrating the advantage of using WPC as a curing agent over PN. Since the WPC was used directly without any digestion or pyrolysis process, the atomic efficiency is 100%, making this WPC recycling strategy economically attractive. The second feature is that we successfully degraded the WPC-cured epoxy thermosets to phenoxy resins through a catalyst-free aminolysis process, that is, the products based on the WPC-cured epoxy thermosets are degradable when their lifespans are expired. The transformation of WPC into epoxy thermosets, along with the degradation of the epoxy thermosets, makes this work attractive for sustainability.