Exploring new diene/dienophile pairs for their integration into covalent adaptable networks

Covalent Adaptable Networks (CANs) are of major interest to sustainability as they offer the potential for performance like themosets with the reprocessability of thermoplastics, thereby enabling options at end-of-life. A range of approaches can be used with Diels-Alder chemistry popular for making dissociative CANs. The aim of this project was to investigate new diene/dienophile pairs that could operate within elevated temperature ranges when compared to that of classic furan and maleimide (60-110 °C). These pairs were then incorporated into prepolymers and subsequently into a range of dissociative CANs with the aim of retaining their structure up to high temperatures before triggering a rDA reaction. Three dienes were investigated to assess their ability to form DA cycloadducts with a variety of dienophiles. Sorbic acid formed a cycloadduct to high conversion with just one dienophile, N-methylmaleimide, proving it to be the least reactive of the three. 9-Anthracenemethanol formed cycloadducts to high conversion with three different dienophiles: N-methylmaleimide, maleic anhydride and citraconic anhydride. Finally, myrcene was found to be the most versatile and reactive diene, forming cycloadducts to high conversion with almost every dienophile with which it was paired. Each of the three dienes were incorporated into prepolymers of varying functionalities and chemistries, which were subsequently reacted with a variety of multifunctional dienophiles to give a range of linear copolymers and crosslinked materials that showed high thermal stability. None of the sorbic acid/maleimide-based materials showed any evidence of dissociation up to 300 °C, however, dissociation was observed for anthracene/citraconimide, anthracene/fumarate and myrcene/acrylate-based materials, which displayed apparent TrDA values varying between 210-247 °C.