How Chain-Folding Crystal Growth Determines Thermodynamic Stability of Polymer Crystals

Chain-folding is a habit of polymer crystallization, which yields limited lamellar thickness of polymer crystals and thus determines their thermodynamic stability. We performed dynamic Monte Carlo simulations of a lattice polymer model with chain-folded lamellar crystal growth stopped by a critical spacing of two parallel-oriented bars. We confirmed the critical spacing as minimum lamellar thickness (lmin) proposed previously in the Lauritzen-Hoffman (LH) model. However, the temperature dependence of excess lamellar thickness beyond lmin appears opposite to the prediction of the LH model. Moreover, it reproduces Strobl et al.’s experimental observations, but our lattice-model approach rules out any mesophase hypothesis. We proposed a kinetic model combining intramolecular secondary nucleation and stem elongation to explain this temperature-dependence behavior, which reconciles the controversial arguments on the microscopic mechanism of lamellar crystal growth of polymers.