Broad line NMR studies of linear and branched polyethylene

Temperature dependence of the shape and linewidth of the broad-line NMR spectra of commercially available high-density polyethylene (PE/HD), low-density polyethylene (PE/LD with ～3 per cent CH₃), block-copolythene (PE/AA with ～3 per cent acrylic acid) and polyethylene single crystal (PE/SC) were investigated to obtain information on the effect of branching and structural changes on the glass-transition temperature (Tg) and activation energy of molecular motion (E). The relatively lower value of Tg ～- ?100° for PE/HD compared to Tg ～- ?85° and ?60° for PE/CH₃ and PE/AA, along with the estimated lower value of E ～- 2·1 kcal/mole for PE/HD compared to 2·6 and 5·1 kcal/mole for PE/CH₃ and PE/AA, respectively, were interpreted by a molecular reorientational process connected mainly with the sidegroups of the main polymeric chains.