Benzyl Thioether: A Dynamic Covalent Motif for Covalent Adaptable Networks

Abstract

Covalent adaptable networks (CANs) have emerged as a promising alternative to conventional thermoset polymers, offering reprocessability and recyclability through the incorporation of dynamic covalent linkages. However, dynamic linkages often compromise the thermal and chemical stability of the polymer, which is essential for many thermosets’ applications. Designing a chemistry that imparts both robustness and efficient dynamicity to the cross-linked polymers is a major challenge. To this end, this report introduces benzyl thioether as a robust and dynamic covalent motif for designing CANs. First, using the small molecular model studies, the dynamic exchange in the thioether was demonstrated and a linear polythioether bearing benzyl thioether was prepared. The CANs were prepared by solvent-free melt polymerization of trifunctional benzyl ether with a linear dithiol. Further on, a series of CANs was prepared, and the properties of these CANs, which include swelling, glass-transition temperature (T_g), and mechanical properties, were tailored by regulating the dithiol chain lengths. The CANs demonstrated excellent thermal and chemical stability owing to the presence of robust thioether linkages. The reprocessability and efficient relaxation of the imposed stress in the CANs at elevated temperature were made possible by the dynamic exchange capability of the benzyl thioether linkage. Impressively, the dynamic behaviors of the CANs were shown to be regulated by monomer chain lengths as well as the catalyst concentration. Finally, degradation of the CANs in the presence of excess thiol was demonstrated. To the best of our knowledge, this is the first study that introduces the benzyl thioether motif for designing the robust and dynamic transthioetherification-based CAN, allowing for the fine-tuning of material properties. This approach will pave the way for the design of robust and sustainable polymeric materials.