Kinetic Study of the Dual-curing of Isocyanate Acrylate Hydrogen Donor Combinations

The dual-curing of an isocyanate functionalized polyurethane-acrylate, associated to an alcohol, was investigated by infrared spectroscopy to address the issue of the curing of coatings in shadow areas on three-dimensional objects. The thermal polycondensation was followed through the decay of the isocyanate group and the photopolymerization through the decay of the acrylate double bond. A number of factors were shown to control the thermal curing, namely the nature of the alcohol, the sample temperature, the atmosphere humidity and the presence of amines. The addition of benzoyl peroxide has a beneficial effect on the curing of the unexposed areas, where hardening occurred upon storage of the sample at ambient temperature. When this initiator was associated to an hydroxyphenyl ketone, dual-curing of a purely acrylate resin could be effectively achieved, with formation of a hard coating in the shadow areas.