The mean-square radius of gyrationS2

the mean-square dipole moment D2

the mean-square end-to-end distanceR2 and their temperature coefficients of unsymmetrical disubstituted poly(methylphenylsiloxane) (PMPS) chains

as a function of stereochemical structure

confomational energies and length of polymers

were studied by using an improved configurational-confomational statistical method based on the rotational-isomeric-state theory. It is found that the increase in isotacticity of PMPS chains causes a significant decrease in the unperturbed dimensions and increase in their temperature coefficients. This correlation of the properties of PMPS and its stereochemical structure is different from that of vinyl monosubstituted polystyrene and disubstituted poly(α-methylstyrene) chains. Dependence of the characteristic ratio of S2on conformational energy Eω’ of C6H5…C6H5 four-bond interactions increases markedly with the degree of isotacticity increasing

the dependence on the conformational energy Eδ and dEσ decreases with increasing the degree of isotacticity. It is also found that the characteristic ratios of R2and its temperature coefficients are in agreement with corresponding experimental results in the degree of isotacticity of about 0-40%. Moreover

the C6H5…C6H5 four-bond interactions play a dominant role in regard to the dimensions of high syndiotactic chains. In addition

the effect of large side groups on unperturbed dimensions is investigated further by the improved expressions ofS2 .