Proton Magnetic Resonance Spectra of Polypropylene in Solution

Abstract

Abstract The application of the NMR method to the study of commercial polypropylene seems to be restricted by some difficulties. A weak thermal degradation technique has therefore been employed to reduce the molecular weight of the polypropylene sample. However, the correspondence between the resultant molecular weight and the resolution of the spectrum is not always unique. A remarkable difference between the NMR spectrum of isotactic polypropylene and that of atactic polypropylene can be found in the methylene resonance region. As an approximation, one may assume that the methylene groups of isotactic polypropylene give rise to the partial spectrum of an ABC2 spin system, whereas those of syndiotactic polypropylene give rise to the partial spectrum of an A2B2 spin system. By means of an electronic computer, the best set of the δ and J parameters for the methylene resonance of isotactic polypropylene has been obtained. The results fit the observed spectrum fairly well. Using this information, the degree of stereoregularity (isotaxy) of a given polypropylene can be calculated. This method is applicable if an well-resolved NMR spectrum is available.