Radiation curable compositions for additive manufacturing of tough objects

A liquid radiation curable composition comprising the following components:

• a) 20 to 60 weight percent of one or more oligomer(s), pre-polymer(s) or polymer(s) containing a plurality of ester linkages in the backbone, at least one urethane group and at least two ethylenic unsaturated groups that can form polymeric crosslink networks with the other components in the composition in the presence of radicals, anions, nucleophiles or combinations thereof;
• b) 30 to 90 weight percent of one or more monomer(s) comprising one ethylenic unsaturated group capable of forming polymeric crosslink networks with the other components in the composition in the presence of radicals, anions, nucleophiles or combinations thereof;
• c) 0.01 to 10 weight percent of one or more photoinitiator(s) capable of producing radicals when irradiated with actinic radiation;
• d) 0 to 40 weight percent of one or more additive(s) selected from the group consisting of:
• filler(s);
• pigment(s), thermal stabilizer(s), UV light stabilizer(s), UV light absorber(s), radical inhibitor(s), and oligomer(s) as a processing aid, wherein said oligomers are different from the oligomers in component a);
• with the provision that component b) is different from the monomers forming the oligomer(s)/pre-polymer(s)/polymer(s) of component a) and the composition has a viscosity of no more than 4000 cps at 25° C.