Researchers prepared two seies of unsaturated polyester resins by reacting maleic anhydride (MAN) with polyethylene glycol (PEG) or polypropylene glycol (PPG). Acid value analysis, hydroxyl value analysis, vapor pressure osmometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy characterized the polyester resins. The researchers compared the molecular structures of the polyester resins with those of idealized resins that had been derived from the reactant stoichiometry. Polyester resins based on MAN and PEG exhibited molecular structures that approximated the ideal(except for PEG 200, which was influenced by the Ordelt reaction). Polyester resins based on MAN and PPG exhibited idealized molecular structures. The presence of a secondary hydroxyl group at the chain ends lengthened the MAN/PPG polymerization times. The PEG based reactive liquid polymers were miscible with the unsaturated polyester resins, but the PPG based reactive liquid polymers were not. 17. refs.