High-resolution solid-state 13C n.m.r. study of isotactic polypropylene gel

• Published in: Polymer (Guilford) 1998-08, Vol.39 (17), p.3905-3908
• Main Authors: Nakaoki, Takahiko, Shuto, Hironori, Hayashi, Hisao, Kitamaru, Ryozo
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; gel; isotactic polypropylene; Organic polymers; Physicochemistry of polymers; Properties and characterization; solid state 13C n.m.r; Solution and gel properties
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(97)10379-2

The molecular conformational structure of isotactic polypropylene (iPP)/ o-dichlorobenzene gel is investigated by means of solid-state high-resolution 13C n.m.r. spectroscopy. It was revealed from the resonance line of methylene carbon at the position generating one γ-gauche effect that the gel-forming crystal takes a 3 1 helical molecular conformation. However, the resonance lines observed for the gel were very broad. In order to deconvolute overlapping peaks, the Lorentzian type peak was converted to Gaussian one by computational analysis. The crystalline component of the resonance line consists of two peaks, of which the chemical shifts were identified with those for the α-iPP crystal. However, the peak intensity ratio of the downfield line to the upfield one in the gel, 1:2, was opposite to the 2:1 ratio in the α-iPP crystal usually reported for melt crystallised films. This is thought to be due to the difference of interchain interaction within the crystal cell. The crystal structure and the crystallinity of the gel were independent of the polymer concentration. The gel-forming crystal did not take a polymer—solvent complex as in the case of polystyrene gel.