Simple Trends in the Methylene Regions of the NMR Spectrum of Poly(propylene) and Ethylene‐Propylene Copolymers

Abstract

The configurational sensitivity of the chemical shift of methylene carbons has been analyzed theoretically in terms of a perturbative approach. Theoretical results and computations have been applied successfully to new experimental data obtained from model compounds of the S αβ resonance. It has been shown that the carbon in β position with respect to the first methine of a regioregular sequence follows the same simple trend of the corresponding carbon atoms in α position. The tiny chemical shift spreadings of the S αβ resonance due to the relative configuration of the nearest methyl groups in α and β position showed a single inversion with respect to theoretical expectation.Decomposition of a chain in subchains.

Author reply

“…The fact that the highest level of sensitivity to stereochemistry is found in the 1 H NMR spectrum is somewhat unexpected. For both polypropylene and for the closely related PLA the 13 C NMR resonances are more sensitive 31. The fairly large spacing of the tacticity‐determining units, five backbone atoms between each lactic stereocenter, in our alternating PLGA copolymers is undoubtedly responsible for this difference.…”