Achieving high elasticity of trans-1,4-polyisoprene with a combination of radiation crosslinking and thiol-ene grafting

Abstract

The mechanical properties of semicrystalline polymers are closely related to crystallization. For trans-1,4-polyisoprene (TPI), to explore the possibility of applications as elastomers, crystallization must be suppressed. Previous studies have shown that, although TPI can be crosslinked by sulfur vulcanization or high-energy radiation, the crystallization of TPI cannot be fully eliminated. In this work, we developed a two-step method to modify TPI. In the first step, TPI is irradiated with γ-ray to obtain crosslinked TPI (xTPI), which has decreased crystallinity. Then, the crystallinity of xTPI is further suppressed by grafting n-dodecanethiol to the xTPI chains by thiol-ene click chemistry. The grafted xTPI (g-xTPI) is characterized by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and wide-angle X-ray scattering (WAXS). The effects of the n-dodecanethiol concentration and reaction time on the grafting degree, crystallization behavior, and mechanical properties are systematically investigated. The results show that the crystallinity of g-xTPI decreases with the grafting ratio. The critical grafting ratio for the “semicrystalline-to-amorphous” transition of xTPI is ∼3%. With the increase of the grafting ratio, the strain recovery of g-xTPI increases from 27.5% to 90%, indicating a transformation from a crystalline polymer to an elastomer.