High resolution solid state 13C NMR spectroscopy of polypropylene with very high syndiospecificity

Abstract

The high resolution solid state 13C NMR spectra were observed for highly syndiotactic polypropylene samples with three kinds of crystalline forms, forms I, II, and III. The forms I and II are the most stable helical conformation, (-TTGG-)2 and all trans planar zigzag conformation, respectively. The sample with the third new crystalline form, form III, was prepared by soaking the sample with form II in toluene at room temperature for two days. The conformation was proposed to be (-T6G2T2G2-). This is based on the comparison of the observed spectrum with the calculated ones with 13C NMR γ-effect for the candidates of the conformation. There are form I (23%) and amorphous component (11%) other than form III (66%) in the sample at 20°C. From the variable temperature NMR experiments of these three samples with predominantly forms I, II, and III, respectively, the transitions among different crystalline forms and amorphous component were discussed.