Effect of Crosslinking on The Stretch-Induced Polymorphic Transition of Trans-1,4-Polyisoprene

Trans-1,4-polyisoprene (TPI) is a typical polymorphic polymer with two crystal modifications. The transition between two crystal modifications (alpha to beta) occurs during stretching. The underlying mechanism is still under debate. In this work, the effects of crosslinking and strain rates on the crystal transition are studied. The TPI, which mainly contains a crystal (alpha-TPI), is crosslinked by gamma-ray radiation. The results show that crystalline morphology does not change after radiation. The melting temperature and yield stress of crosslinked alpha-TPI decrease with the irradiation dose. The structural evolution is studied by in situ wide-angle X-ray diffraction and small-angle X-ray scattering. During stretching, the content of beta crystal (X-beta) of crosslinked alpha-TPI increases in the strain-hardening region. The X-beta is lower in the sample with a higher radiation dose under the same strain. On the other hand, with increasing strain rate, the X-beta of the crosslinked sample exhibits a non-monotonic variation. A parallel mechanical model consisting of amorphous and crystal fibrils is proposed to explain the experimental observations.

Automated summary

This study investigates the effects of crosslinking and strain rates on the crystal transition of trans-1,4-polyisoprene (TPI), a typical polymorphic polymer. The results show that crosslinking does not change the crystalline morphology but decreases the melting temperature and yield stress of the alpha-TPI crystal. Moreover, the content of beta crystal (X-beta) increases with strain in the strain-hardening region and is lower in samples with higher radiation dose. Additionally, the X-beta of the crosslinked sample exhibits a non-monotonic variation with increasing strain rate. A parallel mechanical model is proposed to explain the experimental observations.