Effect of solvent exposure on the properties of hydroxy-terminated polybutadiene-based polyurethanes

Hydroxy-terminated polybutadiene-based prepolyurethanes and diamine chain extended polyurethane-ureas were prepared and treated with various organic solvents in the moisture-cured state in order to modify their ultimate strength. FTIR studies with solvent-treated polyurethanes and polyurethane-ureas confirmed that organic solvents penetrated inside the polyurethane hard segments and affected hydrogen bonding. The polar and non-polar solvents showed different abilities to penetrate into polyurethane hard segments. Solvent treatment after moisture curing increased the tensile strength of these polyurethanes and polyurethane-ureas with respect to control samples. The stress-strain behaviour of solvent-treated polyurethane follows the constrained junction model. The change in hard segment crystallinity on solvent treatment has been explained by wide-angle X-ray diffraction study. The better orientation in polybutadiene soft segments evidenced from SEM (scanning electron microscopy) pictures is believed to be the main reason behind the improved tensile properties of solvent-treated polyurethane samples. The effect of solvent treatment, as well as stretching, on the diffusion coefficient of hexane in polyurethanes was investigated. (C) 2003 Society of Chemical Industry.