13C Nuclear magnetic resonance spectroscopy of polypropylene, 2. 13C spin‐lattice relaxation study in solution

Abstract

AbstractProton‐decoupled partially relaxed FOURIER transform (PRFT) NMR of 13C in natural abundance was used to determine spin‐lattice relaxation times (T1) of individual carbons of polypropylene and polyethylene in o‐dichlorobenzene solution and molten polyethylene. It is shown that the relaxation times of polypropylene carbons are independent of the difference in stereochemical configuration. From the values of the nuclear OVERHAUSER enhancement factor it is shown that the excess energy from equilibrium of all 13C in polypropylene and polyethylene are absorbed into lattice mainly through 13C–1H dipolar interactions. It is shown that the effective rotational motion of the skeletal carbons in polypropylene is isotropic. The activation energies of skeletal and internal methyl motions in polypropylene, separately, and skeletal motion in polyethylen in solutions were estimated from the temperature dependence of the correlation time. The assignment of the two peaks appearing in methine carbon region of polypropylene was briefly discussed.