Acrylated Allophanates - Low viscous alternatives for outdoor applications

Allophanate-containing polyisocyanates are known to exhibit a particularly low viscosity. Therefore, allophanates play an important role in polyurethane chemistry, especially as modified NCO- containing crosslinker molecules in 2k-PUR applications. However, compared to isocyanurate structures allophanates possess a reduced NCO-functionality which in turn reduces the crosslink density of the resulting polyurethane after curing with a polyol compound.
In the field of radiation curing polyurethane acrylates this disadvantage can be overcome by the use of an double bond bearing alcohol to perform the allophanate reaction. This does lead to a comparable functionality and to a higher crosslink density of the cured films as only two HDI molecules are necessary to bear three hydroxyl alkylacrylates rather than three HDI molecules in case of an isocyanurate structure (figure 1). At the same functionality the viscosity of allophanate urethane acrylates is reduced to less than 10% compared to the isocyanurate based material. The first part of this paper will give a deeper insight into urethane induced viscosity effects and how they affect application properties.