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The exterior durability of waterbased UV-cured polyurethane-acrylate (PUA) coatings has been tested in an accelerated QUV-weatherometer. Infrared spectroscopy was used to monitor the chemical changes occurring upon photoageing. The UV-curing reaction was hardly affected by the addition of the HALS radical scavengers and UV absorbers needed to improve the light stability of the UV-cured PUA coatings. The photoinitiator was shown to disappear rapidly upon UV-curing and early QUV exposure. The urethane linkage (C-NH) is the most sensitive to photodegradation. Such waterbased PUA coatings were found to be as resistant to weathering as typical UV-cured PUA coatings. In the presence of light stabilizers, they undergo only minor chemical changes after as much as 4800 h QUV-A ageing. They proved to be as resistant as thermoset two-pack polyurethanes and more resistant than melamine-acrylate thermosets.
