An in Situ X-ray Structural Study of Olefin Block and Random Copolymers under Uniaxial Deformation

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Abstract

The structure, morphology, and orientation development during deformation of an olefin block copolymer (OBC) and an olefin random copolymer (ORC), based on ethylene−octene composition and with similar overall density, were investigated by in situ synchrotron X-ray scattering and diffraction techniques at room temperature and 60 °C. It was found that the original OBC contained only orthorhombic crystals, while the original ORC contained mixed orthorhombic and hexagonal crystals. Under deformation at room temperature, monoclinic crystals were induced in both polymers due to the transformation of orthorhombic crystals under elongation. Under deformation at 60 °C, as monoclinic crystals are thermally unstable, the orthorhombic form became dominant. Upon stretching, the crystal structure in ORC became aligned with a higher degree of orientation along the drawing direction than that of OBC. This different behavior could be attributed to the low chain shuttling agent level of studied OBC, resulting in relatively broader molecular weight distribution and very few hard and soft blocks in one polymer chain, and high octene comonomer content in soft blocks and thus low-density noncrystallizable blocks. Both factors lead to a less effective network structure under deformation than that of ORC with the same density.

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