Influence of crystal thickness and topological constraints on chain diffusion in linear polyethylene

¹³C solid-state exchange NMR is applied to study the influence of morphology on chain diffusion between crystalline and noncrystalline regions in ultrahigh molecular weight linear polyethylene (PE). Lamellar-doubling reduces the exchange rate by a factor of two indicating that the chain diffusion coefficient is largely independent of the lamellar thickness. This is discussed in terms of molecular processes in the crystallites leading to chain diffusion, confirming that the role of defects is minor compared to helical jumps of extended stems. Hindrance of the chain diffusion resulting from chain entanglements was only observed after the chains diffuse over long distances. Moreover, the role of the interphase between the noncrystalline and the crystalline regions on chain diffusion is discussed.