DYNAMIC STUDY OF THE NONCRYSTALLINE PHASE OF C-13-LABELED POLYETHYLENE BY VARIABLE-TEMPERATURE C-13 CP MAS NMR-SPECTROSCOPY

The C-13 spin-lattice relaxation times T1 of C-13-labeled polyethylene crystallized under different conditions were measured at temperatures from -120 to 44-degrees-C by variable-temperature solid-state high-resolution C-13 nuclear magnetic resonance (NMR) spectroscopy, in order to determine accurately the dynamics of the noncrystalline region of the polymer. From these results, it was found that the T1 minimum for the CH2 carbons in the noncrystalline region of solution-crystallized polyethylene with high crystallinity appears at higher temperature by about 20-degrees-C than that of melt-quenched polyethylene with low crystallinity. This means that the molecular motion of the CH2 carbons in the noncrystalline regions is more constrained at a given temperature in the material of higher crystallinity. Furthermore, dynamics of the noncrystalline region is discussed in terms of the C-13 dipolar dephasing times.