The effect of branching on chain diffusion in ultralong n-alkane crystals observed by C-13 NMR

C-13 NMR progressive saturation measurements are used to investigate solid state chain diffusion in semicrystalline alkanes. Monodisperse, ultralong n -alkanes, of 198 and 191 carbon atoms in length, are characterized and prep ared in such a way that they comprise crystals containing chains which are exclusively of once-folded conformation. This preparation is confirmed with DSC and SAXS. The progressive saturation experiments show that the longitu dinal relaxation of magnetisation is consistent with a solid state chain di ffusion process. Reptation and one-dimensional diffusion models are demonst rated to satisfactorily represent the data. The addition of branches to the alkane chains is shown to result in a decrease in the diffusion coefficien t. The obtained diffusion coefficients range from 0.0918 nm(2)s(-1) for the linear chain to 0.016 nm(2)s(-1) for a chain with a branch 4 carbons in le ngth. These diffusion coefficients are consistent with those previously obt ained for polyethylenes.