Analysis of products of the thickening reaction between polyesters and magnesium oxide

Abstract

The products of the reaction between MgO and polypropylene-glycol adipates of different acid values and water contents were analyzed for the water generated and the magnesium reacted into the resin by means of Karl Fischer titration and atomic absorption spectroscopy, respectively. The results conclusively show that both basic and neutral salts are present in the products. The ratio of the amounts of basic and neutral salts present in the mixture, r_B/N, could also be calculated from the results. It was found that as R, the moles of MgO added per mole of acid groups, is increased both the amount of oxide reacted and r_B/N increase while these are relatively unaffected by the water content of the resin. The minimum value of R at which basic salt exists in the reaction products was found to increase with decreasing acid value. It is proposed that diffusional effects account for these observations as well as those reported in literature.