Synthesis and Comparative Physico-chemical Study of Polyester Polyols Based Polyurethanes of Bisphenol-A and Bisphenol-C Epoxy Resins

Polyester polyols of epoxy resins of bisphenol-A and bisphenol-C were synthesized by reacting corresponding 0.02 mol epoxy resin, and 0.04 mol ricinoleic acid by using 1,4-dioxane (30 ml) as a solvent and 0.5 g triethyl amine as a catalyst at reflux temperature for 4–5 hr. Polyurethanes have been synthesized by reacting 0.0029 mol of polyester polyols with 0.004 mol toluene diisocyanate at room temperature and their films were cast from solutions. The formation of polyester polyols and their polyurethanes are supported by IR spectral data (1732.9–1730.0 cm^?1 ester and urethane and 3440.8–3419.6 cm^?1 OH and NH str). The densities of polyurethane of bisphenol-A (PU-A) and polyurethane of bisphenol-C (PU-C) were determined by a floatation method. The observed densities of PU-A and PU-C are 1.2190 and 1.2308 g/cm³, respectively. Slightly high density of PU-C is due to structural dissimilarity of two bisphenols. The tensile strength, electric strength, and volume resistivity of PU-A and PU-C are 34.7, 18.7 MPa; 80.7, 44.4 kv/mm; and 1.7 × 10¹⁵, 2.2 × 10¹⁵ ohm cm, respectively. PU-A and PU-C are thermally stable up to about 182–187°C and followed three step degradation. Incorporation of cyclohexyl cardo group in polyurethane chain did not impart any change in thermal properties but it caused drastic reduction in tensile and electric strength due to rigid nature of PU-C chains. PU-C has excellent chemical resistance over PU-A. Both polyurethanes possess good resistance against water, 10% each of aqueous acids (HCl, HNO₃, and H₂SO₄), alkalis (NaOH and KOH) and NaCl. Good thermo-mechanical, excellent electrical properties, and good chemical resistance of polyurethanes signify their usefulness in coating and adhesive, electrical and electronic industries.