Synthesis of a novel hyperbranched polyester with carboxyl end groups applied to UV-curable waterborne coating

A hyperbranched polyester with carboxyl end group (HPC) was synthesized by using trimellitic anhydride and neopentyl glycol as raw materials via A₂ + B₃ polycondensation. Then, waterborne hyperbranched polyester acrylate (WHPC) was synthesized by partially modifying the carboxylic groups of HPC with glycidyl methacrylate. In order to explore the influence of molecular weight, acrylate groups content, and ion groups content on performances, a series of WHPC films with different molecular weight, acrylate groups content, and ion groups content were prepared. The dynamic light scattering spectrometer analysis shows that the higher ionic groups content and the lower molecular weight cause the smaller particle size. The ionic group content has a positive effect on the solubility. The smaller molecular weight and particle size cause the lower viscosity. The Fourier-transform IR spectrophotometer reveals that the double bond final conversion increased with increasing acrylate groups content. The final conversion is between 69 and 86%. The curing speed is fast, and the curing time is about 70 s due to the numerous end groups owned by the hyperbranched structure. The dynamic mechanical thermal analysis coupled with end-use mechanical property tests illustrates that the crosslink density has a positive effect on the storage modulus and a negative effect on the flexibility. It is also found that glass transition temperature and pencil hardness are determined by the balance between crosslink segment and hyperbranched polyester segment. The thermogravimetric analysis proves that increased crosslink density and molecular weight promote the heat resistance of films. This work utilizes a novel hyperbranched structure that excels in viscosity, flexibility, and water solubility. Furthermore, the preparation process is convenient.