In order to quantify the effect of the clays on the degradation, we have measured the changes in the average molar mass determined by dilute solution viscosimetry (Mv). The values of the intrinsic viscosity, [η], were determined by extrapolation to infinite dilution in chloroform at 25 ± 0.5 °C and the values of Mv were calculated according to the Mark–Houwink–Sakurada equation,