Characterization of a Major Fraction of Disordered All-Trans Chains in Cold-Drawn High-Density Polyethylene by Solid-State NMR

摘要

In cold-drawn,necked high-density polyethylene,solid-state nuclear magnetic resonance (NMR) has identified a major fraction of chain segments intermediate to the ordered crystalline and the almost isotropic amorphous phases.This partially mobile and disordered all-trans fraction in the strain-hardened sample contains 38+-6% of all chain segments in the bulk.Thus,it represents the second largest component in the system,ahead of the disordered gauche-containing or amorphous (17+-4%) and the monoclinic crystalline (4+-2%) phases.A series of one- and two-dimensional NMR experiments,several of which make use of an "inverse ~(13)C T_1 relaxation time filter" for selective observation of the intermediate-component signals,show the intermediate component (or components) to consist of all-trans chains with disordered packing.While the crystalline component has a standard deviation of the chain axis from the draw direction of 1 deg,the intermediate components exhibit an approx 8 deg spread of chain-axis orientations from the draw axis.The chains in the intermediate components undergo fast rotational motions around their axes,with motional amplitudes of ca.20 deg.