Stereochemical configurations of polypropenes by high resolution nuclear magnetic resonance

Abstract

Abstract High resolution hydrogen NMR spectra of amorphous, stereoblock, and isotactic fractions of polypropylene show distinct differences. The spectra are complex but those of polypropene‐2‐ d 1 and polypropene‐2,3,3,3‐ d 4 are simple and easily interpreted. The differences in the spectra of the amorphous, stereoblock and isotactic fractions of the polymers is the result of a difference in the chemical shifts of isotactic and syndiotactic type methylenes. The ratio of the types of methylenes can be estimated from the spectra of polypropene‐2,3,3,3‐ d 4 . In isotactic polymer the concentration of syndiotactic type methylenes is below the limit of detection. Assuming that the inversions in stereochemical configuration are randomly distributed along the polymer chain, the average length of sterically identical segments in stereoblock polymer is about fifteen monomer units. In amorphous polymer the ratio of isotactic to syndiotactic type sequences is approximately one. The spectra of the deuterated polymers show no detectable rearrangement of hydrogen and deuterium atoms in the polymerization.