COOKING SCHEDULE OF ALKYD RESIN PREPARATION .2. EFFECT OF COOKING SCHEDULE ON MOLECULAR WEIGHT DISTRIBUTION OF ALKYD RESIN

The effect of cooking schedule on the molecular weight distribution of an alkyd resin was investigated. At the molar ratio of 1.03/0.43/1.00 for glycerin, lauric acid, and phthalic anhydride, two kinds of alkyd resin were prepared, one by maintaining the reaction temperature at 170°C for an hour and then raising it up to 230°C (sample I), the other by raising the temperature up to 230°C at a uniform rate of 33°C per 10 min. (Sample II). Sample I and sample II were fractionated into seven or eight fractions by adding n‐heptane to 5 wt‐% toluene solution at 30°C. Acid valued, hydroxyl value, intrinsic viscosity [η], and the number‐averagè molecular weight M̄n were determined. The result showed that the molecular weight distribution curve obtained from sample I was much narrower than that from sample II. In addition, a relation was found between [η] and M̄n conforming to the equation [η] = KMα, where different values of K and α were obtained for sample I and sample II. Based on the differences in the molecular weight distribution curves and in the rate constants for the esterification reactions, glycerin/lauric acid and glycerin/phthalic anhydride at 170°C and 230°C, the mechanism of condensation reaction of short oil alkyd resin was discussed. Copyright © 1969 John Wiley & Sons, Inc.