An investigation study of controlled synthesis of polyester polyols having different molecular weights

Polyester polyols are the second most important group of oligo-polyols for production of polyurethanes after polyether polyols. Polyester polyols have stable and specific practical applications due to some superior characteristics of the resulting polyurethanes. The superior characteristics polyester polyol based polyurethanes are explained by a better crystalline structure in the urethane segment, compared to the majority of polyether polyols which are amorphous, due to the superior secondary forces between the polyester chains and also due to a superior thermal and fire resistance, compared to polyether polyol based polyurethanes. Polyester based polyurethanes, have a superior solvent resistance compared to the polyether-based polyurethanes. Polyester polyols were employed in both rigid and flexible polyurethane formulations. The most important segments of polyester polyol applications are those of polyurethane elastomers, flexible foams, coatings, adhesives, rigid foams, synthetic leather and sealants. The main objective of this work to develop controlled synthesis of polyester polyols with different structure and different moleculer weight from dicarboxylic acids and various glycols by polyesterification reaction. The process conditions were optimized by the temperature profile and also point of vacuum distillation. In this work, these diols are used; ethylene glycol, di-ethylene glycol, glycerin, trimethylol propane, sorbitol. These dicarboxylic acids are used; adipic acid, phthalic anhydrid, teraphatlic acid. Different dicarboxylic acids with a number of various glycols were used as raw materials to give distinct molecular weight and structures with specific features. The reaction was carried out at temperatures in the range of 190-200 0C for the synthesis of low molecular weight polyesters, while a temperature above 200-220 0C was maintained to guarentee the polyester has higher molecular weight. For controlled molecular weight polyester polyesterification, these critical factors during the reaction are important, reaction temperature, reaction time, the agitation, raw materials, flow of inert gas and also grateful removal water. Confirmation of a successfully conducted process of polyesterification was obtained by FTIR-ATR spectroscopy (Infrared Fourier Transform-Attenuated Total Reflectance), as well as viscosity ,acid number and hydroxyl number determination. Different molecular weights and structures can be achieved for polyester polyol synthesis, to import certain features to the final application, since the polyester polyol is an intermediary product, used as a raw material for polyurethane production.