Easily recycled thiol-ene elastomers with controlled creep

Abstract

Starting from in-house synthesized allylic monomers containing dynamic disulfide (SS) bonds, a set of vitrimeric thiol-ene elastomers were prepared and characterized with respect to their viscoelastic and tensile properties. A mixture of a disulfide-containing diallyl monomer and disulfide-free diallyl, namely diallyl phthalate, was combined stoichiometrically with a thiol crosslinker, trimethylolpropane tris (3-mercaptopropionate), to obtain soft thiol-ene thermosets with varying degrees of dynamic bond content. The materials were able to relax strain induced stress completely and rapidly at moderately high temperatures when the disulfide content was above a certain threshold, which was accurately predicted by a statistically-based network (de)crosslinking model. Relaxation of materials with disulfide content below this threshold required the activation of an additional transesterification bond exchange process by increasing the temperature. Recycling of the materials could be achieved by hot-press molding at convenient temperatures. Especially in low-disulfide containing materials, changes were observed in the material structure and properties with increasing number of reprocessing cycles. However, a significant reduction in ambient temperature creep was observed upon reducing the disulfide content. The disulfide content can be easily optimized to yield minimal loss of mechanical property and minimal creep. This work opens up new avenues for the cost-effective development of vitrimeric elastomers with minimal ambient temperature creep.