Impact of molecular weight and comonomer content on catalytic hydrogen-deuterium exchange in polyolefins

The effect of molecular weight (MW) and comonomer content (CC) on the catalytic hydrogen-deuterium exchange process (CHDEP) in a series of polyethylenes has been studied using a band filter based SEC-IR method. CHDEP permits deuterium labeling of polyolefins prepared by any synthetic route, a major advantage over the traditional method of polymerizing deuterated monomers. However, incompleteness in deuterium-exchange as well as heterogeneity in deuterium distribution are known challenges to deuterium labeling of heterogeneous polymers by this method. These factors complicate small angle neutron scattering (SANS) studies, in which the average deuterium-exchange level (DL) and deuterium distribution are critical. A band-filter based size exclusion chromatography (SEC)-infrared absorption (IR) technique is presented as a simple but accurate method to quantify the DL as a function of MW. The DL of a series of ethylene-alpha olefin copolymers has been found to increase with MW but does not depend strongly on CC for all the polyethylene samples. This behavior has been further confirmed with independent measurements of average DL as a function of weight-averaged MW of a series of fractions from a deuterated linear low density polyethylene. The SEC results for the fractions are in agreement with deuterium measurements on the fractions using NMR spectroscopy, density and FTIR.