MOLECULAR-DYNAMICS SIMULATION OF SUBSTITUTED POLYACETYLENES

Molecular mechanics and molecular dynamics calculations have been applied to several substituted polyacetylenes. Results for the barrier height for single-bond rotation for polyacetylene were compared to experimental values and quantum mechanics results for low molecular weight models of polyacetylene in order to check the methodology. As side groups increase in number and size in polypropyne, polybutyne, and poly(tert-butylacetylene), the backbone conformation becomes increasingly nonplanar. For poly[1-(trimethylsilyl)-1-propyne] barriers for rotation about a backbone single bond are approximately 40 kcal/mol. Thus the chain conformation achieved during polymerization will be maintained, though fluctuations in dihedral angles in narrow potential energy wells do allow significant changes in the chain contour.