HYPERBRANCHED ALIPHATIC POLYESTERS

Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1200-44 300 were synthesized in the molten state from 2,2-bis(hydroxymethyl)propionic acid (repeating unit of AB(x) type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (core molecule) using acid catalysis. The synthesis procedure was a pseudo-one-step reaction where stoichiometric amounts corresponding to each generation were added successively. The resulting polymers were glassy, slightly yellow solids at room temperature with hydroxyl groups as terminal groups. The degree of branching of the polyesters was determined with the help of model compounds using C-13-NMR and was found to be near 80%. The material exhibited good thermal stability as analyzed with TGA in a nitrogen atmosphere. Glass transition temperatures were determined using DSC and were found to be about 40 degrees C and to be relatively insensitive to variations in molar mass.