The unperturbed dimensions for a series of poly (methyl methacrylates) with Bernoullian distribution of stereochemical composition has been studied. A technique involving a gel permeation chromatography coupled with capillary viscometer was used for this purpose. The effect of the column dispersion of the GPC columns on the measurement of unperturbed dimension has been discussed. It has been shown that the experimental results are in good agreement with the values predicted by Monte Carlo calculation.A modified equation has been proposed to calculate the unperturbed dimension of the polymers with asymmetric substitutents and independent internal rotations. The parameters

K and a of [n]=KMafor a series of stereoregular PMMA in tetrahy-drofuran at 30℃ has also been determined.