Conformational Statistics of Poly(dimethylsiloxane). 1. Probability Distribution of Rotational Isomers from Molecular Dynamics Simulations

The probability distribution of isomeric conformations in poly(dimethylsiloxane) has been investigated both by conformational energy considerations and by molecular dynamics simulations. A comparatively smooth distribution of isomeric states is obtained from both approaches. The molecular dynamics trajectory of a simulated dimethylsiloxane oligomer of eight units is used as a reliable and realistic tool to estimate the probability of occurrence for various rotational isomeric states. Conformations involving bonds in the gauche state produce attractive intramolecular potentials through suitable spatial arrangement of close neighbors, which is contradictory to the unfavorable interactions attributed to them in the model described by Flory, Crescenzi, and Mark. The relative potential energies of the various conformational states are obtained from the probability of those conformations occurring in a molecular dynamics simulation.