Recyclable, Degradable, and Fully Bio-Based Covalent Adaptable Polymer Networks Enabled by a Dynamic Diacetal Motif

Covalent adaptable networks (CANs), which can reconfigure on-demand under photo-or thermal stimuli, have recently been pursued as an alternative to the traditional thermosetting polymers. While these materials have demonstrated excellent recyclability and reprocessability, the majority of them reported to date are based on non-renewable resources. Mean-while, material recycling highly counts on the collection system, and any materials that inevitably escape from the collection system will eventually go to the environment, challenging nature's ability to break down these materials. Therefore, CAN materials that possess both recyclability and degradability are highly desirable. In this work, we seek to simultaneously address the recyclability, renewability, and degradability of CAN materials. Spiro diacetal building blocks are derived from bio-based benzaldehyde and erythritol and then subjected to the curing process using bio-based epoxy soybean oil as crosslinkers, yielding fully biobased CAN materials. Owing to the dynamic and degradable features of acetal motifs, our CAN materials exhibit both good recyclability and acid degradability, and the degraded products are reusable for preparation of new CANs. In addition, by tuning the steric hindrance adjacent to the reactive phenol site, we are able to control the mechanical properties of CANs using different bio-based benzaldehydes (vanillin, ethyl vanillin, and syringaldehyde). The outcome of the current research provides a strategy for the design of recyclable and degradable bio-based CANs, which will extend the development of CANs.