Cycloaliphatic polyester based high solids polyurethane coatings: I. The effect of difunctional alcohols

High-solids polyesters were synthesized with two cycloaliphatic diacids, 1,4- cyclohexanedicarboxylic acid (1,4-CHDA) and 1,3-cyclohexanedicarboxylic acid (1,3-CHDA); and with five diols, 1,4-cyclohexanedimethanol (CHDM), neopentyl glycol (NPG), hydroxypivalyl hydroxypivalate (HPHP), 2-butyl-2-ethyl-1, 3-propanediol (BEPD), and 1,6-hexanediol (HD). The viscosity of the polyesters was dependent on the structures of diols. The viscosity of polyesters is lower with the diol HD, intermediate with BEPD and HPHP, and higher with the diols CHDM and NPG. The polyesters were crosslinked with hexamethylene diisocyanate isocyanurate (HDI isocyanurate) affording polyurethane coatings. The mechanical properties, tensile properties, fracture toughness, and viscoelastic properties were investigated for the polyurethane films with five different diols. The cyclohexyl structure of the CHDM provides the polyurethane with rigidity which is manifested in high tensile modulus, hardness, and fracture toughness. In contrast, the linear diol, 1,6-hexanediol provides polyurethane with very high flexibility, but these coatings suffer with respect to low hardness and tensile modulus. Polymers and Coatings Department, Fargo, ND 58105. 3401 Grays Ferry Avenue, Philadelphia, PA 19146.