Chain-End Modifications Suppressing Lamellar Thickening of Short Semicrystalline Polymers under Isothermal Annealing: Molecular Dynamics Simulations

Coarse-grained molecular dynamics simulations are employed to investigate the effect of chain-end modifications on the lamellar thickening in short-chain semicrystalline polymers during isothermal annealing. Analysis of transformation patterns reveals the coexistence of chain-sliding and melting–recrystallization mechanisms. Lamellar thickening proceeds via a two-step mechanism of nucleation and growth. Nucleation preferentially occurs in regions enriched with nonfolded chains, with a critical nucleus size of approximately 30 stems. Two lamellar growth modes during recrystallization are identified: crystallization at the lateral growth front and direct insertion of amorphous chains into existing lamellae through one of the two end surfaces. Introduction of bulky chain ends significantly suppresses lamellar thickening by sterically hindering the unfolding-insertion mechanism. These results elucidate the microscopic mechanisms of lamellar thickening and underscore the pivotal role of chain-end size in modulating polymer crystallization.