Variable trends of chain-folding in separate stages of strain-induced crystallization of bulk polymers

Abstract

We performed dynamic Monte Carlo simulations of isothermal crystallization of bulk polymers at a high temperature, which was induced by a homogeneous stretching with a constant strain rate over a wide range of strains. We observed that the crystallites exhibit variable trends of chain folding in three sequential regions of strains, revealing hierarchical mechanisms of strain-induced polymer crystallization: in the first region, sporadic stretched segments initiate intermolecular crystal nucleation with less chain folding at higher strains; in the second region, massive less-stretched segments perform crystal growth with more chain folding at higher strains; in the third region, those folded chains extend via a melting-recrystallization process, again with less chain folding at higher strains. Different trends of chain-folding between crystal nucleation and growth appear intrinsic and ultimately lead to shish-kebab crystals. Our observations provided a molecular-level rationale to understand various experimental phenomena upon the processing for oriented semi-crystalline polymers.