Molecular weight distribution of poly(ethylene adipate) and its changes caused by aging



Precipitation fractionations of poly(ethylene adipate) were carried out by nonsolvent addition methods using chloroform as solvent and petroleum ether as nonsolvent. Seventy-five grams of the polyester was fractionated into 10 fractions by stepwise method and 35 g of the former was fractionated into nine fractions by triangle method. Number-average molecular weights were determined by ebullioscopic measurements with chloroform as solvent. Acid, hydroxyl, and saponification numbers were determined by analytical methods. It was proved that poly(ethylene adipate) contained considerable quantity of cyclic molecules (ca. 23 mol %). The molecular weight distribution curves of linear molecules constructed from the results of polyester fractionations were found to differ rather from distribution expected from the theory of kinetics of polycondensation and statistical theory. This discrepancy may be explained by higher reactivity of functional groups belonging to shorter molecular chains. It was found out that the aged poly(ethylene adipate) hydrolyzed to a great extent and practically contains no cyclic molecules. Molecular weight distribution of the aged poly(ethylene adipate) determined by GPC is very near to the theoretical “most probable distribution” derived for polycondensates.