From alkanes to polyethylene: the onset of chain folding in polymer crystallization

N-alkanes of uniform chain length used span the conventional extended chain crystallization behaviour of paraffinoid substances and chain folded crystallization of polyethylene. As such, they serve as models for exploring the origin and nature of chain folding, the characteristic mode of crystallization of flexible macromolecules. New advances will be presented together with general implications for polymer crystallization. The main findings, which apply to both melt and solution crystallization are as follows: The chains start to fold at chain lengths between 100 and 150 carbon atoms with fold length (ℓ) increasing with crystallization temperature (T_c). In the final stage of crystallization ℓ is an integer fraction (IF) of the chain length.