Characterization of a polypropylene elastomer: Chain microstructure, heterogeneity, morphology and deformation behavior.

摘要

A thermoplastic elastomer derived from polypropylene using an unbridged 2-arylindenyl metallocene catalyst has been investigated. The physical, morphological, and deformation properties of the elastomeric polypropylene (ePP) were studied by a variety of methods: fractionation, chromatography, thermal analysis, acid digestion, microscopy, spectroscopic analysis, optical polarimetry, and scattering techniques. Despite its low crystallinity (∼10% by differential scanning calorimetry and X-ray diffraction) and low isotacticity ([mmmm] = 34%), we have demonstrated for the first time that elastomeric polypropylene can crystallize to form morphological structures reminiscent of those found in classical semi-crystalline polymers. Large hierarchical structures (spherulites, hedrites, cross-hatching, and lamellae) were observed, which suggest that there exist long crystallizable isotactic segments chemically attached to amorphous atactic segments (stereoblock microstructure).;Deformation characteristics of the elastomeric polypropylene were investigated by mechanical tests and optical methods: rheo-optical birefringence, X-ray scattering, and neutron scattering. Tensile properties and deformation characteristics of polypropylene elastomer were compared to those of its solvent fractions. The role of each fraction residing within the elastomer was investigated in situ using small-angle neutron scattering (SANS) by doping a small amount of deuterated fraction in the elastomer. Co-crystallization was observed between the low-tacticity fraction and the high-tacticity components of the propylene elastomer.