13C n.m.r. and X-ray diffraction studies of the morphology of alkanes and linear polyethylenes

Abstract 13 C n.m.r. spin-lattice relaxation times have been determined for carbons in a number of solid alkanes and in two linear polyethylenes. 13 C spin-lattice relaxation times, T 1s , for the internal methylene carbons of the linear alkanes depend upon structure and chain length. There is almost a 100-fold increase in T 1 in going from orthorhombic C 21 H 44 to C 60 H 122 . The central methylene carbons in the two polyethylenes give rise to two exponential decays. Analysis of the methyl resonances in one of these polyethylenes suggests that 60% of the methyl ends are in a crystalline environment. Low molecular weight orthorhombic alkanes are more mobile than expected from the 1 T 1 versus a dimension of the unit cell relationship observed for linear and branched polyethylenes.