A method advanced recently is used to estimate the characteristic ratio C∞ for statistical butadiene-styrene and butadiene-acrylonitrile copolymers from the reported data of the limiting viscosity number and sedimentation coefficient. The results are compared with those of the traditional methods. The dependences of C∞ on the copolymer composition are discussed and interpreted in terms of steric and/or dipole-dipole interactions of adjacent monomeric units.