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On the alkali saponification of ethylene-vinyl acetate copolymer (EVAc) in heterogeneous system, the effect of preliminary partial saponification (p-EVAc) was examined. p-EVAc membrane was saponified with a sharp moving boundary in it, giving a linear rate curve as in the case of EVAc reported previously. The reaction rate of p-EVAc presaponified to 33.0% of the acetyl group became 40 times of that EVAc at 30°C and 24 times at 35°C, despite of the increased zero-shearing viscosity by the partial presaponification. The reaction rate and the accerelation effect caused by the presaponification increased with an increase of acetyl group content of the polymer. These results were explained as follows. The saponification of p-EVAc proceeded with a rate determining step of boundary reaction whose phenomenon resembled “Case II type diffusion” The acceleration effect of the resaponification in this reaction was caused by the adsorption of alkali ion on hydroxyl groups near the acetyl groups in the reacting boundary.

THE ACCELERATION EFFECT OF PRELIMINARY PARTIAL SAPONIFICATION ON THE RATE OF HETEROGENEOUS ALKALI SAPONIFICATION OF ETHYLENE-VINYL ACETATE COPOLYMER