Configuration-dependent properties of poly(dimethylsiloxane) chain

The intermolecular rotational potential energies for poly(dimethylsiloxane) (PDMS) chains are directly obtained from a priori probability P-alpha beta. Here the differing statistical weight matrices for the Si-O and O-Si bonds are considered in calculating the configuration partition function. In the Bahar's model, as the same statistical weight matrices for the Si-O and O-Si bonds are adopted, there exists a large deviation of a priori probability P-alpha beta between the theory and the molecular dynamics (MD) simulation. Our model gives satisfactory agreement with experiment on the mean-square unperturbed end-to-end distance, the mean-square dipole moment and its temperature dependence, and the molar cyclization equilibrium constants for dimethylsiloxane oligomers. This new rotational isomeric state approach can be widely applied to other chains; such as -CH2-C[(CH2)(m)H](2)- and -O-Si[(CH2)(m)H](2) for arbitrary m.