New insight into stretch induced structural evolution of α trans-1,4-polyisoprene characterized by real time synchrotron WAXS and SAXS measurements

Abstract

Real time synchrotron wide angle and small angle X-ray scattering (WAXS and SAXS, respectively) were used to characterize the stretch induced structural evolution of α trans-1,4-polyisoprene (trans-PI). 2D WAXS results indicated two ensembles of crystalline modifications with distinctive orientation modes coexisted during stretching. Stretching transformed part of the monoclinic α phase into highly oriented orthorhombic β phase at strain e = ~0.4. The β phase had rather high orientational degree with polymer chains parallel to the stretching direction, while the orientational degree of α phase was much lower. Complemented by qualitative 2D SAXS analysis, it was found that amorphous layer deformation and intralamellar chain slip dominated at different stretching stage. The melt and recrystallization process of α phase which led to the formation of β phase was also investigated. Formation of two interpenetrating networks of crystalline skeleton (constructed by residual α and β crystals) and amorphous entanglement accounted for the stress-hardening in the late stage.