LOW VISCOSITY SELF-TOUGHENING ACRYLATE COMPOSITION Compositions comprising: A) A mixture of acrylate functional prepolymers in the total amount of between about 50% and 80% by weight of the composition, said prepolymer mixture comprising a first prepolymer which is a urethane diacrylate resin, suitably a polyether urethane diacrylate, having a viscosity of at least 500,000 cps at 25.degree.C in an amount of between 10 and 40% by weight of the composition, and a second multi-acrylate prepolymer having a viscosity of between about 500 and 50,000 cps in an amount of at least 15% by weight of the composition; B) A monoacrylate diluent monomer selected from the group consisting of isobornyl acrylate, .beta.-carboxyethyl acrylate and mixtures thereof in an amount of at least 5% by weight of the composition; and, C) An effective amount for cure initiation of a free radical initiator, the composition having a viscosity of less than 10,000 cps at 25.degree.C, give unusual selftoughened cured properties. Such compositions, where the free radical initiator is a free radical photoinitiator, are particularly useful in rapid prototyping applications where the requirement for low viscosity and optical clarity of the liquid formulation has heretofore limited use of the formulations to ones giving undesirably brittle or soft properties.
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