Preparation and characterization of aqueous polyurethane dispersions containing ionic centers

Aqueous polyurethane dispersions were prepared from toluene di‐isocyanate, polytetramethylene glycol, and 1,4‐butanediol, with different weight percent of dimethylol propionic acid (DMPA) as anionic center. IR Spectroscopy was used to follow the polymerization reaction as well as the polymer characterization. The effect of DMPA content on the state of dispersion, particle size distribution, mechanical, and thermal properties of the emulsion‐cast films were studied. Average particle size of the prepared emulsion polyurethanes decreased with increasing DMPA content. Tensile strength and hardness increase and elongation at break and contact angle decrease by increasing the ionic content. Glass transition temperature (Tg) shifted toward higher temperature and thermal stability decreased by increasing the DMPA content. The increased Tg and tensile properties are interpreted in terms of the increased hard segments and coulombic forces between ionic centers. The decreased contact angle is ascribed to the increase in the hydrophilicity of the polyurethanes because of the incorporation of more hydrophilic moiety in polymer backbone.