| abstract |
Distortion control additives are disclosed which comprise a polyisocyanate, a polyol or polyol blend having a hydroxyl functionality of 2 to 3 hydroxyl groups per molecule and an average molecular weight of at least about 500 grams per gram mole, a diol chain extender having from about 2 to 35 carbon atoms per molecule and an acrylate or methacrylate having an acrylate functionality of from 1 to 5 acrylate groups per molecule. Ultraviolet-curable liquid compositions comprising an unsaturated polymeric resin, a monomer and the distortion control additives of the present invention are also disclosed. The distortion control additives can provide substantial reductions in distortion, e.g., shrinkage, of objects produced by ultraviolet curing, e.g., stereolithography. |