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Phase transitions of the rapid‐compression‐induced mesomorphic isotactic polypropylene under high‐pressure annealing

Author:
Fu, Xiaobo, Jia, Wenxia, Li, Xiaoting, Wang, Yaming, Wang, Zhen, Liu, Chuntai, Shen, Changyu, Shao, Chunguang
Source:
Journal of polymer science 2019 v.57 no.11 pp. 651-661
ISSN:
0887-6266
Subject:
annealing, crystallization, differential scanning calorimetry, polypropylenes, small-angle X-ray scattering, temperature, wide-angle X-ray scattering
Abstract:
The mesomorphic isotactic polypropylene was prepared by rapid compression instead of the common method of temperature quenching, and their phase transition under high pressure was investigated in depth by combining wide‐angle X‐ray diffraction, small‐angle X‐ray scattering, and differential scanning calorimetry techniques. It was found that annealing under pressure can promote the further arrangement of chain segments of the mesophase toward the crossed state in the orthorhombic γ‐phase, and the long period of the mesophase slightly decreased from 8.2 to 7.2 nm. The kinetics of this meso‐γ transition strongly depends on pressure. As annealing pressure increased, the mobility of molecular segments was reduced, and then the onset and finishing time of phase transition were both delayed significantly. A critical annealing pressure was found between 1.6 and 1.75 GPa, which determines whether the phase transition occurs or not. When pressure reaches 1.75 GPa, mesophase did not transform at all within 120 min. Based on the results, a reasonable mechanism was proposed to show the crystallization process of mesophase under high‐pressure annealing. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 651–661
Agid:
6438076