MEAN-SQUARE RADIUS OF GYRATION OF POLYSILOXANES

The mean-square radius of gyration for polysiloxanes has been derived according to the exact definition. Taking account of the examples of s ymmetrically substituted poly(dimethylsiloxane) and unsymmetrically su bstituted poly(methylphenylsiloxane), we find that the dependence of [ S-2] On the molecular weight follows the general formula [S-2] = aM(b) with b = 1 +/- 0.016, which is analogous to the theoretical outcomes for vinyl or vinylidene polymers even though the skeletal bone of poly siloxanes consists of alternating heteroatoms. A numerical comparison of the rigorous expression of the mean-square radius of gyration given in this paper with that reported by Flory shows that the difference i s obvious for low-molecular-weight polymer and it gradually declines w ith increasing degree of polymerization.