Microstructure of 2,3 erythro di-isotactic polynorbornene from atomistic simulation

A new RIS model was developed for erythro di-isotactic polynorbomene that included long-range steric interactions that are needed to properly model its conformation. These interactions were included by extracting RIS states from an approximate energy state map for the heptamer of this polymer. The RIS model predicted a novel helix-kink conformation for this polymer in which helices were occasionally disrupted by a backbone kink and a value of approximately 1.9 for the exponent a from the Mark-Houwink-Sakurada equation at the theta condition. These RIS results were consistent with independent single chain Monte Carlo simulations and were also used to generate bulk periodic structures of this polymer. The results of these simulations compare well to both experimental viscometry and wide angle X-ray diffraction results for two polymer samples synthesized using Pd and zirconocene homogeneous polymerization catalysts. These results indicated that the likely stereochemical configuration for polymers produced using these catalysts is the erythro di-isotactic form. They also suggested that polymers of similar structure such as cis poly(t-butyl acetylene) may also adopt this kink-helix conformation. (C) 2000 Elsevier Science Ltd. All rights reserved.