Self-photoinitiating water-diluted polyurethane acrylates and their UV-curing kinetics

In order to find a novel solution to eliminate the photolysis residues and migration problems of organic photoinitiators, a new kind of self-photoinitiating oligomers of water-diluted polyurethane acrylate (WPUA) was synthesized. The UV-curable WPUAs were synthesized with toluene diisocyanate, polyether diols, 2, 2-dimethylol propionic acid, hydroxyl propyl acrylate, pentaerythritol triacrylate, and triethylamine. The UV-curable WPUAs were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography, thermogravimetry, differential scanning calorimeter, and UV-Vis spectroscopy, respectively. Effects of different neutralizers, neutralization degrees, hydroxyl acrylates, double bond contents, soft and hard segment ratios on UV-curing degrees and properties of UV-cured films were investigated. The real time UV-vis spectra during the UV-curing process were measured. The UV-curing kinetics of WPUA at low concentrations were conformed to be zero order reactions. The results showed that the UV-cured films had the best performance when triethylamine was used as the neutralizing agent, the neutralization degree was 100%, the initiation molar ratio of -OH and -NCO was 5, and the molar ratio of pentaerythritol triacrylate and 2-hydroxyethyl methacrylate was 3:2. A novel self-photoinitiating mechanism with neutralized triethylamine in WPUA was proposed. Thus, the novel self-photoinitiating WPUAs were proved to be effective and sufficient to use in UV-curing coatings.