H NMR Analysis of Chain Unsaturations in Ethene/1-Octene Copolymers Prepared with Metallocene Catalysts at High Temperature

Abstract

In this paper, we report the full resonance assignments in the olefinic region of the 600 MHz 1H NMR spectra of a typical ethene/1-octene copolymer (4.0 mol % of octene units) produced with a metallocene catalyst at high temperature, and of an ethene homopolymer prepared under similar conditions for comparison. The assignments were based on a thorough analysis of 1D (1H, 1H{1H}, 13C) spectra and of 2D 1H−1H (COSY, TOCSY) and 1H−13C (HSQC, DEPT-HSQC) maps. Thirteen different olefinic structures were identified, and their formation explained in terms of plausible mechanistic paths associated with the high polymerization temperature. The fraction of internal chain unsaturations traceable to allylic activation turned out to be comparable to that of terminal ones in both samples. Despite its complexity, the said spectral region is now amenable to deconvolution and full simulation in terms of known and recognizable patterns, and usable for fast (possibly on-line) measurements of chain unsaturation degree, as we...