Unsaturated polyesters with maleic acid and different molar ratio of phthalic anhydride to adipic acid were produced, mixed with styrene, and cured. The degree of double bonds conversion, determined by differential scanning calorimetry (alpha(DSC)), indicating the initial curing, increases significantly with the molar ratio of phthalic anhydride. On the other hand, the degree of double bonds conversion of maleate (alpha(UP,FTIR)) and styrene (alpha(St,FTIR)) units determined by Fourier transform infrared spectroscopy after prolonged curing are considerably higher than alpha(DSC) and increase slightly with the molar ratio of phthalic anhydride. Polyester containing phthalic anhydride without adipic acid (M5P5) has the lowest tetrahydrofuran uptake and diffusion parameter D/alpha(2) due to its more rigid segments, in opposite to polyester containing adipic acid (M5A5) having the highest values. According to dielectric spectroscopy measurements, two different relaxations were determined, one beginning above 130 degrees C (with peak above 180 degrees C) attributed to alpha-relaxation (dielectric glass transition) and a second one at lower temperatures, attributed to beta-relaxation. The peak of beta-relaxation is at around 130, 75-80, and 30 degrees C for the rigid, intermediate rigidity/flexibility, and flexible polyesters, respectively. The alpha-relaxation is determined at low frequencies and the beta-relaxation at intermediate or high frequencies. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1984-1993, 2011