Rotor‐synchronized two‐dimensional 13C CP/MAS NMR studies of the orientational order of polymers. I. High‐performance ultrahigh molecular weight polyethylene fibers

The orientational order of three morphological components, identified previously as two crystalline components, C1 and C2, and an amorphous component, A of four polyethylene fibers, including two gelspun ultrahigh molecular weight (PE‐I and PE‐II) and two meltspun moderate molecular weight (PE‐D and PE) polyethylene fibers are further analyzed by rotor‐synchronized two‐dimensional 13C CP/MAS (ROSMAS) nuclear magnetic resonance (NMR) techniques. Our results indicate that the orientational order of these components differ substantially among themselves in a given fiber and among different fibers of the same component. Values of β1/2, the polar angle at which the orientational distribution function (ODF) P 〈β〉 decays to half its maximum, are determined to be: 18° (C2 of PE‐II), 21° (C2 of PE‐I), 29° (C2 of PE‐D), 31° (C1 of PE‐I) and 50° (C2 of PE). No orientational sideband can be detected for component A, suggesting that the A component is due to the amorphous domain. The implication of this results and the technical limit of this technique are analyzed.