Exploring Polymeric Diene–Dienophile Pairs for Thermoreversible Diels–Alder Reactions
Daniel MacKinnon, Ben Drain, C. Remzi Becer
Abstract
High Resolution Image Download MS PowerPoint Slide The thermoreversible Diels–Alder (DA) reaction provides access to reversible thermosets and thus a pathway to their circular recycling. However, the known thermoreversible diene–dienophile DA pairs are very limited and primarily involve the furan–maleimide pair; hence, there is a need to investigate novel pairs that can provide thermal reversibility in chemical binding at higher and lower temperatures. Hence, a set of 24 diene–dienophile pairs are screened for their tendency to undergo a Diels–Alder (DA) reaction at temperatures up to 140 °C. Of the 21 viable DA pairs, 16 DA pairs then successfully underwent gelation in an analogous polymer cross-linking system. The viability of the thermoreversible retro-Diels–Alder (rDA) reaction at elevated temperatures was then studied via a dissolution study, dynamic scanning calorimetry, and dynamic mechanical analysis. Two novel pairs were shown to undergo rDA degelation for the first time in a polymeric system. [Anthracene-9-methanol + citraconimide] and [anthracene-9-methanol + monomethyl fumarate amide] underwent degelation at 277 and 247 °C, respectively. Several additional novel gels showed dissolution at temperatures up to 250 °C, suggesting that their rDA processes may be accessible, albeit at higher temperatures. The partial self-healing of these two thermoreversible gels at temperatures of 100 and 150 °C, significantly below their degelation temperatures, is also demonstrated.