The effect of chemical degradation of two diblock copolymers of poly(ethylene oxide) (E) and poly(lactide) (L), E39L5 and E39L20, on their adsorption at silica and methylated silica was investigated with in situ ellipsometry. Steric stablization of polystyrene dispersions was investigated in relation to degradation. Hydrolysis of the poly(lactide) block of the copolymers was followed at different temperatures and pH by using HPLC to measure the occurrence of lactic acid in solution. The block copolymers were quite stable in pH-unadjusted solution at low temperature, whereas degradation was facilitated by increasing temperature or lowering of the pH. Lower degradation rates of E39L20 where observed at low temperature in comparison with those of E39L5, whereas the degradation rates of the copolymers were quantitatively similar at high temperature. The adsorption of the copolymers at methylated silica substrates decreased with increasing degree of degradation due to the reduction in the ability of hydrophobic block to anchor the copolymer layer at the surface. At silica the adsorption initially increased with increasing degradation, particularly for E39L20 due to deposition of aggregates onto the surface. After extensive degradation the adsorption of the copolymers at both silica and methylated silica resembled that of the corresponding poly(ethylene oxide) homopolymer. Overall, it was found that the eventual reduction in adsorption occurred at a lower degree of degradation for E39L5 than for E39L20 Mean-field calculations showed a reduced anchoring for the block copolymers with decreasing poly(lactide) block length at hydrophobic surfaces. In accordance with this finding, it was observed that polystyrene dispersions were stabilized by E39L20 or E39L5 in a way that depended on both the lactide block length and the degree of degradation. Upon degradation of the hydrophobic block, stabilization of the polystyrene dispersions was maintained initially, but eventually degradation resulted in destabilization. The average residual copolymer concentration required for stabilization of the polystyrene dispersions was much higher than the corresponding concentration of intact copolymer required for stabilization. (C) zool Academic Press.