Synthesis and Properties of Ionic Polyurethane Dispersions: Influence of Polyol Molecular Weight

Aseries of water dispersible polyurethanes containing carboxylate anion as the hydrophilic pendant group were prepared from toluene diisocyanate (TDI), 1,4butanediol (1,4-BDO), dimethylol propionic acid (DMPA) and different molecular weight of polytetramethylene glycol (PTMG). IR Spectroscopy was used to check the end of polymerization reaction and characterization of polymer.The effect of PTMG molecular weight was studied on the particle size distribution, contact angle, and mechanical and thermal properties of the emulsion-cast films. Average particle size of prepared polyurethane emulsions decreases with increasing the PTMG molecular weight. Tensile strength and hardness decrease and elongation-at-break and contact angle increase with increase of the PTMG molecular weight. Thermal property and thermal stability are also affected by variation of PTMG molecular weight. The thermal stability increases with increasing PTMG molecular weight. Glass transition temperature (Tg) moved toward the lower temperatures by increasing molecular weight of the polyol. Decrease in Tg and tensile properties are interpreted in terms of the decrease in hard segments and the increase in chain flexibility and phase separation in high molecular weight PTMG based polyurethanes.