AbstractThe intrinsic viscosities of solutions of polyvinylpyrrolidone (PVP) in water‐sodium dodecyl sulphate have been measured, for four different molecular weights of PVP, and different concentrations of sodium dodecyl sulphate at temperatures between 20 and 35°C. The exponentaof the Mark‐Houwink‐Sakurada equation has been determined, and the values of the short range interaction parameterKθ,and expansion factor αηderived. Above a certain concentration the sodium dodecyl sulphate is adsorbed on the polymer by means of hydrophobic attractions, and the consequent repulsion between anionic heads provokes expansion of the macr