| abstract |
Process for the continuous preparation of unsaturated polyesters, comprising bringing olefinically unsaturated dicarboxylic acids or their anhydrides, if desired, together with saturated dicarboxylic acids of their anhydrides (dicarboxylic acid component) and dihydric alcohols, if desired, together with higher polyhydric alcohols (alcohol component) into contact in molar ratios of from about 1.5:1 to 1.95:1 in a first reaction phase, operating at a temperature of from about 100* to 160*C and with residence times of from about 5 to 40 minutes to cause the formation of a corresponding half-ester; adding to the half-ester formed a further quantity of the alcohol component in such a way as to give a molar ratio of the dicarboxylic acid component to the total amount of the alcohol component in the range of from about 0.87:1 to 0.97:1; bringing about the polyesterification in a second reaction phase by treating the product obtained in at least two separate and successive stages, which are operated at decreasing pressure values in the range of from about 5 atmospheres to atmospheric pressure, for times of about 2 to 8 hours, and at temperatures of from about 100* to 220*C, the temperature in said stages not differing by more than about 10*C, and the water formed during the polyesterification being eliminated from each of the said stages; evaporating the residual water and the excess of the alcohol component from the polyesterification product obtained with operation at pressures below atmospheric pressure. |