NUCLEAR-MAGNETIC-RESONANCE DETECTION OF 2 DISTINCTLY DIFFERENT CHAINSIN THE ORTHORHOMBIC CRYSTALLINE PHASE OF POLYETHYLENES

Several commercial and noncommercial, high- and low-density and ultrao riented polyethylene samples, as well as polyethylene samples with ino rganic fillers, have been investigated by inversion-recovery cross-pol arization magic angle spinning carbon-13 nuclear magnetic resonance (N MR). In all these samples two types of all-trans chains in orthorhombi c crystalline domains are detected, which give two overlapping carbon- 13 lines with different line widths and different relaxation times. Fr om the NMR relaxation parameters we conclude that one type of the crys talline chains, which composes 60-90% of the crystalline fraction in a ll samples, can execute at room temperature 180 degrees flips with a f requency in the kilohertz domain. The other crystalline chains are mor e rigid and probably are found in more perfect structures in which suc h chain flips do not occur or occur on a much slower time scale. Addin g kaoline filler particles to polyethylene enhances the contribution o f the more mobile crystalline chains. The presence of the two distinct ly different types of crystalline environments is found in all polyeth ylene samples investigated so far (more than 25 samples).