Lattice Model for Crystal—Amorphous Interphases in Lamellar Semicrystalline Polymers: Effects of Tight-fold Energy and Chain Incidence Density

Abstract

The partition function for polymer chains in the interphase of lamellar crystallites has been evaluated by the enumeration of the different ways of placing chain segments on a lattice. In essence, we have reformulated the earlier work of Flory, Yoon, and Dill. In the case of fully flexible chains involving no conformational energy for tight-folds, our expression for the partition function reduces to the form reported by Marqusee and Dill, who derived their partition function through probabilistic, space-filling arguments. However, the inclusion of an energy term Endisfavoring tight-fold conformations is found to decrease significantly the fraction of regular adjacent folds and increase the thickness of the interphase. Quantitative results from our calculations are in good agreement with the Monte Carlo results of Mansfield. The effect of the chain incidence density at the crystal surface on the fraction of regular adjacent folds is also examined, and we show that both these factors are important in determining the structure of the crystal-amorphous interphase. © 1989, American Chemical Society. All rights reserved.