Distinct Thiol- and ROS-Induced De-Crosslinking Mechanisms in Printable and Bioactive Sulfur-Based Covalent Adaptive Networks

Abstract

Abstract Here we present our systematic investigation on how thiols and reactive oxygen species (ROS) affect the de-crosslinking behavior and thermal properties of sulfur-based covalent adaptive networks (CANs) prepared with novel photo-crosslinkable poly(ε-caprolactone) lipoates (PCLLAs). By integrating experimental data with the Flory-Rehner theory, we reveal the distinctions between the two de-crosslinking degradation processes in terms of crosslinking density, gel fraction, swelling ratio, and their impact on the thermal and antioxidant properties of PCLLA networks. Thiols in good solvents rapidly and reversibly cleave disulfide crosslinks to sharply reduce the crosslinking density and to enhance chain mobility, leading to increased melting point (Tm) and unchanged crystallinity of the network. Dynamic mechanical analysis further showed that thiol-induced de-crosslinking progressively reduced high-temperature storage modulus retention while increasing viscous dissipation. In contrast, ROS in aqueous solutions can cause slow and irreversible oxidative scission of disulfide bonds in the networks, resulting in increases in both Tm and crystallinity. The 3D printability of PCLLAs and the intrinsic antioxidant activity of the networks are also demonstrated. This study shows that the de-crosslinking kinetics and material properties of sulfur-based CANs can be efficiently tuned by regulating the de-crosslinking pathways, providing a strategy for designing degradable, stimuli-responsive, and functionally programmable polymer networks.