Abstract: A simple and convenient procedure for the transforming the Cheng-Yan instrinsic visco-sity-molecular weight equation with three paramaters,A,B, and K_θ:[η] = K_θ[ A +(1 + AB)M^1/2 + BM] into a lincar equation of M^1/2:([η]-[η]_o/(M^1/2-M_o^1/2)= [K_θ(1 + AB)+ K_θBM_o^1/2] + K_θBM^1/2 was proposed.The unper turbed dimension of polydimethylsiloxane obtained from the deducedequation is in agreement with the results from the empirical equations such as KF, SF and IF equations. The new equation avoids the arbitrainess of the empirical equations inestimating the unperturbed dimension.

Key words: polydimethylsiloxane, viscosity molecular weight equation, unperturbed dimension