Dynamic disulfide cross-linked polycaprolactone grafted CO2-based poly(ester-co-carbonate): Effective crystallinity, enhanced mechanical performance, reversible de-crosslinking, and degradability

Developing novel and degradable cross-linked graft copolymers without sacrificing mechanical robustness, processability, recyclability, and reusability is highly attractive and equally challenging. Here, we report the preparation of dynamically disulfide (S-S) cross-linked polycaprolactone grafted CO₂-based poly(ester-co-carbonate) through a combinatorial way. This polymer is characterized by a degradable poly(ester-co-carbonate) as backbone, polycaprolactone (PCL) side chains, and dynamic S-S linkages formed by ring-opening polymerization (ROP) of cyclic disulfide groups induced by heating as cross-linking junctions. A series of cross-linked graft copolymers with varied lengths of semicrystalline and flexible PCL side chains were synthesized. These copolymers crystallized effectively, with mechanical strength and extensibility varying with the side chain lengths. Crystallization, synergistically with dynamic S-S cross-links improved mechanical strength, compared to molten or non-cross-linked systems. The S-S cross-linked network was introduced through thermoplastic processing, endowing polymers with reversible network transitions. Specifically, dynamic dissociation of S-S can occur through thiol-disulfide exchange guaranteeing the cross-linked polymers with reversible de-crosslinking properties. Furthermore, these de-crosslinkable and recyclable polymers could undergo transition from sol to gel state, based on thiol-disulfide exchange facilitating the generation of new S-S intermolecular cross-links. Notably, these cross-linked graft copolymers could undergo efficient base-catalyzed alcoholysis-induced degradation forming oligomers (590 g/mol) due to the presence of abundant aliphatic ester or carbonate ester groups. This strategy offered an effective method to obtain cross-linked graft copolymers with thermal processability, crystallization, mechanical performance, reversible de-crosslinking, and degradability. These desirable properties indicate the promising application prospects of the cross-linked graft copolymers prepared in recyclable and degradable flexible devices, degradable thermoforming packaging, flexible degradable drug controlled-release membranes and highly deformable degradable soft robots, etc.