CHAIN COLLAPSE BY ATOMISTIC SIMULATION

In order to study the collapse of polymer chains, atomistic simulations of atactic poly(vinyl chloride) (PVC) were performed. An isolated PVC chain with a degree of polymerization (DP) larger than 40 quickly folds from an all-trans zigzag form into a nearly spherical compact state, whose density is close to the bulk one. PVC chains with DP < 30 remain unperturbed. The radius of gyration (S) and the monomer clustering exhibit two-stage and three-stage processes for the chain collapse, respectively. In the first stage, nearest monomers stick together and both the end-to-end distance and S sharply decrease. The shape of the chain changes from a thin wire to a sausage. The second stage corresponds to the transition from a sharp to gradual decrease in S. During this stage, distant monomers along the contour start coming within an interaction radius of each other. The third stage is characterized by an appearance of self-entanglements. In the collapsed chain, no new torsion states develop but the distribution becomes richer in gauche(+/-) states than in the unperturbed chain.