Chain Configurations in Lamellar Semicrystalline Polymer Interphases

A mean-field lattice theory is developed to describe the configurations of long-chain molecules at the crystal/amorphous interface in semicrystalline polymers. Chains are assumed to satisfy continuity and space-filling requirements. The theory permits systematic levels of approximation for correlations among neighboring bonds along the chains subject to the interfacial constraints. We consider the two lowest levels of approximation here: (i) single bonds (two segments) or (ii) bond pairs (three segments). Both models predict that approximately 73% of the chains which emerge from the crystal reenter at sites which are immediately adjacent and that the interfacial region should therefore be small, provided the chains are freely flexible. The models predict that the ratio of chain loops to ties in the amorphous region is smaller, and the mean lengths are greater, than predicted by random walk models.