Polyolefin Miscibility: Solid-State NMR Investigation of Phase Behavior in Saturated Hydrocarbon Blends

Abstract

Polyolefin blends represent a vital material field due to their economic and commercial importance. Potential new properties such as lighter weight, lower cost and higher strength, motivate research to investigate blends of saturated hydrocarbon polymers. However, many questions remain concerning how polymer chain structure and packing influence local thermodynamics, or more specifically, the interplay between enthalpy and entropy, which ultimately control bulk phase behavior. Solid-state NMR has proven to be an essential tool in these studies due to its ability to selectively observe molecular level conformations and dynamics without isotopic labeling. Combinations of basic and advanced variable temperature studies such as 1D and 2D 13C cross-polarization exchange experiments, static 2H lineshape analysis, 1H relaxation/spin-diffusion measurements, and 129Xe experiments were applied in this work. Several systems were studied, including 50/50 weight percent blends of polyisobutylene with polyethylene-co-1-butene, polyisobutylene with head-to-head polypropylene, and atactic polypropylene with the same polyethylene-co-1-butene samples. The results were used to determine a relationship between miscibility, length scales of mixing, and timescales/length scales of the glass transition.