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

H-1 and C-13 NMR spectra and H-1 spin-lattice relaxation times T-1 and T-1rho 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 alpha, beta and gamma-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 C-13 resonance characteristic to the monoclinic structure in addition to the orthorhombic observed in both polymers. The crystallinity degree derived from T-1rho in studied polymers is close to that determined using DSC method. (C) 2002 Elsevier Science Ltd. All rights reserved.