Hyperbranched waterborne polyurethanes

A hyperbranched polyol (HBP), viz. hyperbranched 2,2-bis(hydroxymethyl) propionic acid (MPA) polyester-16-hydroxyl, was incorporated chemically into waterborne polyurethane by a covalent bond as a multifunctional chain extender or chemical crosslink for isocyanate (NCO)-terminated PU prepolymers. In addition, the effects of HBP incorporation on the particle size, tensile properties in the glassy and rubbery states, thermal stability, contact angle, and hardness were examined. After HBP incorporation, the particle size initially decreased during the dispersion step. With time, the particle size increased due to the swelling of HBP, and there was an increase in the contact angle, initial modulus, break strength, and decomposition temperature of the dispersion cast film. In particular, the largest increases in these properties were obtained when the NCO index was unity.