| abstract |
The invention relates to the acceleration of the synthesis of unsaturated polyesters containing maleic acid/anhydride, 1 to 30 percent, preferably 5 to 15 percent of the prescribed maleic acid/anhydride is introduced into the reaction mixture in total or in two or more increments at the stage of the reaction when the acid number or the molecular weight of the mixture has reached about 50 to 250 or about 300 to 1500, respectively. Thus, the rate of polyesterification can be increased considerably, occasionally two-folds and, in addition, polyester resins of very low acid number or high molecular weight can be prepared. |