Photopolymerization kinetics of UV-curable polyester powder coatings containing urethane methacrylate reactive diluents

Abstract A series of small molecule urethane methacrylates were synthesized and used as reactive diluents for UV-curable polyester powder coatings. A UV-curable polyester oligomer was prepared and formulated with the reactive diluents and a photoinitiator package. Kinetics studies were carried out using photo-differential scanning calorimetry (photo-DSC). The influence that the reactive diluent concentration, UV-light intensity, temperature, and atmosphere had on the reaction kinetics was investigated. Crosslinked samples that were analyzed via DSC showed that the glass transition temperature correlated well with the extent of conversion. In general, lower curing temperatures (i.e., ≤ 80°C) significantly reduced the conversion and polymerization rate. However, the use of a mono-functional reactive diluent facilitated much higher conversions than the UV-curable polyester control, even at just 5 wt% loading level. These findings suggest that reactive diluents can be used to improve the low temperature cure capability of UV-curable polyester powder coatings.