HIGH-RESOLUTION SOLID-STATE C-13 NMR-STUDY OF ISOTACTIC POLYPROPYLENEGEL

The molecular conformational structure of isotactic polypropylene (iPP )lo-dichlorobenzene gel is investigated by means of solid-state high-r esolution C-13 n.m.r. spectroscopy. It was revealed from the resonance Line of methylene carbon at the position generating one gamma-gauche effect that the gel-forming crystal takes a 3/1 helical molecular conf ormation. 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 crys talline component of the resonance line consists of two peaks, of whic h the chemical shifts were identified with those for the alpha-iPP cry stal. However, the peak intensity ratio of the downfield line to the u pheld one in the gel, 1:2, was opposite to the 2:1 ratio in the alpha- iPP crystal usually reported for melt crystallised films. This is thou ght to be due to the difference of interchain interaction within the c rystal cell. The crystal structure and the crystallinity of the gel we re independent of the polymer concentration. The gel-forming crystal d id not take a polymer-solvent complex as in the case of polystyrene ge l. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.