Effect of Crosslinking on the Stretch‐Induced Polymorphic Transition of Trans‐1,4‐Polyisoprene

Abstract Trans ‐1,4‐polyisoprene (TPI) is a typical polymorphic polymer with two crystal modifications. The transition between two crystal modifications ( α to β ) 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 α crystal ( α −TPI), is crosslinked by γ ‐ray radiation. The results show that crystalline morphology does not change after radiation. The melting temperature and yield stress of crosslinked α −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 β crystal ( X β ) of crosslinked α −TPI increases in the strain‐hardening region. The X β is lower in the sample with a higher radiation dose under the same strain. On the other hand, with increasing strain rate, the X β 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.