hydroxy - functional polyester oligomers are prepared by contacting a hydroxy - functional aliphatic dicarboxylic acid or a mixture of dicarboxylic acids containing hydroxy - functional aliphatic diacids , with a diglycidyl ether or diglycidyl ester in the presence of an onium catalyst in an ether solvent under conditions suitable for forming the oligomer . the oligomers can be used as hot melt adhesives , adhesive tackifiers , plasticizers , heat - curable adhesives and heat - curable coatings . some of these materials are biodegradable and are therefore suitable for application to compostable end products .