Determination of Chain-Folding Structure of Isotactic Polypropylene in Melt-Grown alpha Crystals by C-13-C-13 Double Quantum NMR and Selective Isotopic Labeling

作者：Li Zhen; Hong You lee; Yuan Shichen; Kang Jia; Kamimura Akihiro; Otsubo Akihiro; Miyoshi Toshikazu

来源：Macromolecules, 2015, 48(16): 5752-5760.

DOI：10.1021/acs.macromol.5b01321

Chain-folding (CF) patterns, successive CF number < n >, and fraction < F > of C-13 CH3 15% labeled isotactic polypropylene (iPP) in melt-grown crystals at two crystallization temperatures (T(c)s) of 100 and 150 degrees C were investigated using C-13-C-13 Double quantum (DO) NMR and spin-dynamics simulation. The former provided the alpha(1) packing structure while the latter lead to the alpha(2)-rich sample with an alpha(2) fraction of ca. 57%. It was demonstrated that the iPP chains adopt small cluster structures consisting of 6-8 stems connected via adjacent re-entry as mean structures in both alpha(1) and alpha(2) phases. There was no kinetic effect on < F > and < n > values, while kinetics did influence the folding directions of the chains under the assumptions of configurational and packing constraints. It was concluded that the CF process occurs at the growth front and dominates the chain-packing process of iPP alpha phases in a wide T-c.

• 出版日期2015-8-25