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 β_1/2, 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. © 1993 John Wiley & Sons, Inc.