Role of Rigid–Amorphous chains on mechanical properties of polypropylene solid using DSC, WAXD, SAXS, and Raman spectroscopy.

We evaluated the rigid–amorphous (RA) fraction of isotactic polypropylene (iPP) samples by various measurement techniques and investigated the role of the RA chains on the mechanical properties of iPP. The RA fraction was increased by annealing above the α -relaxation temperature, although the RA fraction was almost independent of the molecular weight. The RA fraction obtained by differential scanning calorimetry increased linearly with the number of consecutive helical chains with 12–14 monomer units, suggesting that the RA chains are attributable to crystalline defects. Moreover, the α -relaxation temperature varied linearly with the RA fraction; the RA chains present as crystalline defects were removed from the crystalline structure by α relaxation. The yielding region of the stress–strain curve became broad by increasing the RA fraction; the fragmentation strength of the lamellar crystals was widely distributed owing to the large number of crystalline defects. [Display omitted] • We evaluated the rigid–amorphous fraction of isotactic polypropylene. • A large number of rigid–amorphous chains were located in crystals as defects. • Rigid–amorphous chains are excluded from the crystals by annealing at 100 °C. • The yielding deformation broadened with increasing rigid–amorphous fraction. [ABSTRACT FROM AUTHOR]