Uniformity of Partial Deuteration in Narrow-distribution High-density Polyethylene Prepared by Saturation of Polycyclopentene over Homogeneous Catalysts

Isotopic labeling - replacement of hydrogen (H) with deuterium (D) - is often required for
small-angle neutron scattering, which allows measurement of polymer chain dimensions in bulk and thermodynamic interactions in blends. It is highly desirable to achieve a uniform distribution of D at both the intra- and inter-chain levels, such that scattering contrast is evenly imparted along and between chains. We describe narrowly-distributed and uniformly partially-deuterated polyethylenes (DPE), prepared by ring-opening metathesis polymerization of cyclopentene followed by catalytic deuteration with either carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) or Wilkinson’s catalyst. While density measurements, as well as FT-IR and ¹³C NMR spectroscopies, all indicate approximately 20% deuteration in both DPEs, as expected from deuterium addition across the double bonds in the polycyclopentene precursor, ¹³C NMR spectra reveal that Wilkinson’s catalyst produces more regular labeling (83% vicinal D) than the Ru-based catalyst (39%). Further analysis of isotopic shifts and multiplicity gives insights into the mechanisms of isomerization and the H/D exchange reactions that occur concurrently with deuteration using these catalysts.