Investigation of the Molecular Mechanisms of Melting and Crystallization of Isotactic Polypropylene by in Situ Raman Spectroscopy

• DOI: 10.1021/acs.macromol.7b00229
• Publication Date: 2017-07-21T14:18:55Z
• Authors: Yusuke Hiejima; Kento Takeda; Koh-hei Nitta
• Keywords: Tacticity; Supercooling

In situ Raman spectroscopy has been used to reveal the molecular behavior of isotactic polypropylene during melting and crystallization. The 400 cm–1 band assigned C–C–C bending shows a blue-shift heating, suggesting an increase in conformational disorder, whereas 1330 CH2 twisting red-shift owing interchain distance. We suggest that expansion proceeds even melt state, while chain conformation becomes sufficiently disordered at point. During cooling process, peak shifts given temperatures are essentially same as those except for supercooled region where show obvious hystereses. By extrapolating linear correlation between shift characteristic length along axis, critical stem size crystallization is estimated be ∼2.4 nm.