Molecular dynamics in polyethylene and ethylene-1-butene copolymer investigated by NMR methods

1H and 13C NMR spectra and 1H spin–lattice relaxation times T1 and T1ρ have been employed to study the structure and molecular dynamics in polyethylene and ethylene-1-butene copolymer in the temperature range from 100 to 370 K. Results are interpreted in terms of α, β and γ -relaxation, as well as methyl group rotation. The activation energies for all motions were established. The incorporation of 1-butene into ethylene chain leads to an increase of mobility in amorphous and crystalline phases as well as appearance the 13C resonance characteristic to the monoclinic structure in addition to the orthorhombic observed in both polymers. The crystallinity degree derived from T1ρ in studied polymers is close to that determined using DSC method.