Relationship between the structure and hydrolysis rate of unsaturated polyester prepolymers

Polyester prepolymers based on binary, ternary or quaternary combinations of the following monomers: maleic anhydride (MAA), isophthalic acid (IPA), propylene glycol (PG), neopentyl glycol (NPG), ethylene glycol (EG) and diethylene glycol (DEG) were synthesized and immersed in water at 100 degrees C. The hydrolysis rate was determined by acid titration of chain ends; the rate constants were of second order and independent of hydrophilicity. Fumarates are intrinsically 5-20 times more reactive than phthalates. NPG, PG and DEG esters have very close reactivity. In contrast, EG esters are considerably more reactive. In copolymers, the whole hydrolysis rate cannot be deduced from the data relative to the corresponding homopolymers by a simple linear relationship; copolymers appear more stable towards hydrolysis than would be predicted. The rate constants obtained on model compounds were used to predict the hydrolysis behaviour of the corresponding styrene crosslinked networks. It appeared that the proposed method gives a good order of magnitude for the rate constant but with systematic overestimation. (C) 1997 Elsevier Science Limited.