In this paper the results in the field of unsaturated polyesters of our teams’ research, together with the results published in the literature by other researchers, are overviewed. Unsaturated polyesters based on ethylene glycol or propylene glycol were synthesized using a variety of anhydride, saturated and unsaturated dicarboxylic acids and different catalysts. The progress of the polyesterification was followed by determining the amount of water produced during the reaction. The kinetics of the polyesterification was studied and a mathematical model for the simulation of the production of unsaturated polyesters was deduced from the experimental results of the produced water. Two fundamental equations were expressed: an empirical equation and a theoretical one, which contain as parameters the kinetic constants of polycondensation, e.g. activation energy, and which were determined from the above- mentioned kinetical study of the reaction. Further, the determination of the parameters for theoretical as well as the empirical equation was done at different ranges taking into consideration the time from the beginning of heating. This model can be used if the water can be continuously separated and measured.
After the polyesterification, the polymers were diluted with styrene and then cued by using a common, room temperature curing system (methylethylketone peroxide, cobalt naphthenate). The curing was studied using Differential Scanning Calorimetry (DSC) by dynamic- and isothermal-heating conditions, or rheologically. The FTIR-spectra of the initial polyesters and polyesters cured were also determined. Curing at the end of DSC scan is not completed and the mean degree of conversion (α) of all double bonds (styrene unit and maleate unit) was approximately determined as α = 0.40. Using an appropriate kinetic model for the analysis of the curing reactions’ exotherm, the activation energy (Ea), the reaction order (x) and the frequency factor (ko) were determined. Because the kinetic parameters (i.e. Ea, ko, x) differently affect the kinetics, the curves of degree of conversion versus time (t) at various isothermal conditions is preferable in order to compare and characterize the curing of polyesters. The degree of conversion of already crosslinked polyesters is highly increased by post-curing them at elevated temperature and prolonged time.
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