Synthesis, photopolymerization kinetics, and thermal properties of UV-curable waterborne hyperbranched polyurethane acrylate dispersions

A series of UV-curable waterborne hyperbranched polyurethane acrylate dispersions (WHBPUADs) were prepared via a three-step procedure based on isophorone diisocyanate (IPDI), hyperbranched polyester (HBP), maleic anhydride (MA), and hydroxy-ethyl acrylate (HEA). The structure of WHBPUADs was characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). FTIR was also applied to research the effect of double bond concentration on the kinetics of photopolymerization. The heat resistance of the cured films was characterized by thermogravimetric analysis (TGA), and their mechanical properties were also measured. The results showed that the double bond conversion (τ) and photopolymerization rate (R _p) were affected by the concentration of double bond and viscosity of WHBPUADs. The UV-curable systems with higher double bond concentration and lower viscosity led to higher τ and R _p. The maximum τ and R _p reached 93% and 71 mmol g⁻¹ s⁻¹, respectively. The WHBPUADs films possessed better heat resistance and mechanical properties, and with the increase of crosslink density, the heat resistance and hardnesses were further improved.