Polydicyclopentadiene (pDCPD) is a high-performance thermoset whose unusual oxidative sensitivity has long been recognized but is not mechanistically understood. Here we identify singlet oxygen (1O2) as the primary oxidant and the pendant cyclopentene ring as the primary site of reactivity that together drive the intrinsic oxidative degradation of pDCPD. Controlled 1O2 generation, model compound studies, and weathering experiments reveal a chemoselective oxy-ene pathway that selectively converts cyclopentene units into cyclopent-2-en-1-ones and initiates allylic-hydroperoxide-driven cross-linking. In contrast, main-chain alkene models and studies on pH2DCPD─in which the cyclopentene unit is saturated to suppress oxy-ene reactivity─show that the main-chain alkene follows a slower β-scission pathway. These mechanistic distinctions explain the long-observed oxidative instability of pDCPD and clarify why polymers lacking the pendant cyclopentene, such as pH2DCPD, offer improved resistance to oxidative aging. Guided by this insight, oligo-DCPD fragments are transformed into polar, benzyl-acrylate-miscible, polyfunctional additives whose enone groups enable tunable cross-linking during radical acrylate polymerization. Together, these results connect the molecular origin of pDCPD oxidation to both monomer design principles and selective macromolecular editing strategies.
Zhou et al. (Mon,) studied this question.