Kinetic Selection of Chain Folds under Entanglement Constraint.

How to fold long-chain molecules under entanglement topological constraints is a long-standing challenge in polymer crystallization. Using molecular dynamics simulations, we observe that polymer chains undergo directional reptation toward the growth front, demonstrating the existence of an along-chain force that drives disentanglement and facilitates tight-fold formation. Our results seminally reveal a linear scaling between the tight-fold fraction and the reciprocal of the entanglement length. This scaling originates from the regulation by entanglement and chain rigidity: the former limits the physical scale at which the segment can fold, whereas the latter determines the difficulty of bending the chain segment into a tight fold within confined space.