Synthesis and properties of waterborne hyperbranched aliphatic polyester clear coats

A waterborne hyperbranched polyester (WHP) consisting of a multi-hydroxy functional aliphatic polyester core, which is endcapped with an epoxy group of CARDURA E10 and salt-like groups in different ratios was synthesized. The core was a second generation of hyperbranched aliphatic polyester Boltorn™ H20 with approximately 16 hydroxyl groups. The effects of different ratios of chemical structure of end groups were studied by evaluating various properties of WHP such as acid value, solubility in water and dynamic viscosity. A natural good control over the solubility of the samples was possible by salt-like functionality. Since acid value decreased as reaction time increased, it gave an indication of the end of the reaction when the change in acid value was small. The investigation of solubility characteristics of the modified hyperbranched polyester illustrated that those with higher concentration of salt-like groups were more soluble while those having less salt-like groups were less soluble. The viscosity of the resin WHP was reduced rapidly by diluting with water and raising the temperature. The performance of film, baking with waterborne hyperbranched polyester and hexamethoxy methyl melamine resin (HMMM) at 140 °C, was excellent. The glass transition temperature (Tg) of product decreased after modification. Therefore, the waterborne curable resins based on hyperbranched polyester were regarded as an alternative strategy as waterborne clear coats.