Synthesis and Thermo-Selective Recycling of Diels–Alder Cyclopentadiene Thermoplastics

Catalyst-free and reversible step-growth Diels-Alder (DA) polymerization has a wide range of applications in polymer synthesis and is a promising method for fabricating recyclable thermoplastics. The effectiveness of polymerization and depolymerization relies on the chemical building blocks, often utilizing furan as the diene and maleimide as the dienophile. Compared to the traditional diene-dienophile or two-component approach that requires precise stoichiometry, cyclopentadiene (Cp) can serve dual roles via self-dimerization. This internally balanced platform offers a route to access high-molecular-weight polymers and a dynamic handle for polymer recycling, which has yet to be explored. Herein, through a reactivity investigation of different telechelic Cp derivatives, the uncontrolled cross-linking of Cp was addressed, revealing the first successful DA homopolymerization. To demonstrate the generality of our methodology, we synthesized and characterized six Cp homopolymers with backbones derived from common thermoplastics, such as poly(dimethylsiloxane), hydrogenated polybutadiene, and ethylene phthalate. Among these materials, the hydrogenated polybutadiene-Cp analog can be thermally depolymerized (