The shear viscosity of poly(vinylchloride) (PVC) at 200 degrees C can be decreased by at least one order of magnitude by the addition of as little as 5 wt% poly n-alkyl(meth)acrylates (PMA) of a much lower dynamic viscosity than PVC. For this effect to be observed, the polymeric additive must be immiscible with PVC at 200 degrees C. The average size of the dispersed phases is observed in the range of 0.5 to 5 mu m; size fluctuation in this domain has no significant effect. When these conditions are met, there Is a linear increase in the shear viscosity ratio eta(blend)/eta(PVC) from 0.2 to 1.0 with increasing logarithmic values of the dynamic viscosity ratio of the additive over PVC[log(eta(P(MA)*)/eta(pvc)*) from -4 to -1].