Dual Role of Nitroxide in Achieving Performance-Advantaged Polydicyclopentadiene: Radical Initiator and Antioxidant

Radicals play a dual role in chemical processes; that is, they not only facilitate reactions that enhance performance but also induce degradation, such as thermal-oxidative aging in polymers. This duality significantly limits the development of high-performance thermosets such as polydicyclopentadiene (PDCPD). Herein, this work addresses this challenge by incorporating a nitroxide-monomer-containing norbornene derivative (NT) into PDCPD via sequential ring-opening metathesis polymerization (ROMP) and radical reactions. The nitroxide moiety serves as both a radical initiator to increase cross-link density and scavenger of radicals that induce aging. With the assistance of controls, the role and structural evolution of the nitroxide moiety at elevated temperatures was elucidated. Sequentially, NT was copolymerized with dicyclopentadiene (DCPD) via sequential ROMP-radical reactions, leading to PDCPD with enhanced mechanical and antiaging properties. This work proposes an effective strategy for designing performance-advantaged, antiaging polymers by leveraging radicals to enhance polymer performance while simultaneously mitigating their detrimental effects on aging.