Enhanced Crystallinity of Disulfide Network through UV Irradiation-Activated Bond Exchange

Crystallinity in polymers plays a critical role in enhancing mechanical strength, thermal conductivity, and electrical conductivity. Here, disulfide bonds were incorporated into a polymer network containing ethylene chains, and the effect of UV-activated bond exchange on crystallinity was investigated. Differential Scanning Calorimetry (DSC) revealed that both the melting enthalpy and melting temperature continuously increased with UV irradiation, as the disulfide bond exchange facilitates the reorganization of polymer chains and promotes the formation of larger crystallites. The experimental temperatures used were well below the temperature to thermally activate bond exchange, allowing the contributions of disulfide exchange and thermal effects to be isolated. With only thermal annealing, the melting temperature increases but not the enthalpy attributed to thicker crystalline domains. Crosslinks fix the chain ends and limit further rearrangement beyond the strand length scale and maintain a constant crystallinity. The degree of crystallinity was also analyzed using infrared spectroscopy and AFM, which indicated higher crystallinity and increased stiffness for UV treated networks.