Dynamic study of the noncrystalline phase of 13 C‐labeled polyethylene by variable‐temperature 13 C CP/MAS NMR spectroscopy

The 13 C spin‐lattice relaxation times T 1 of 13 C‐labeled polyethylene crystallized under different conditions were measured at temperatures from −120 to 44°C by variable‐temperature solid‐state high‐resolution 13 C 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 T 1 minimum for the CH 2 carbons in the noncrystalline region of solution‐crystallized polyethylene with high crystallinity appears at higher temperature by about 20°C than that of melt‐quenched polyethylene with low crystallinity. This means that the molecular motion of the CH 2 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 13 C dipolar dephasing times.