R₁ is C₃-C₁₀ cycloalkyl or C₆-C₁₀ aryl, wherein the C₃-C₁₀ cycloalkyl and C₆-C₁₀ aryl are unsubstituted or substituted with one or more substituents selected from C₁-C₆ alkyl and C₁-C₆ alkoxy;

R₂ is H or CH₃;

the R₃'s are each independently C₁-C₆ alkyl or C₁-C₆ alkoxy;

n is an integer from 0 to 4; and

X and Y are each independently absent or C₁-C₃ alkylene, with the proviso that, when R₁ is C₆-C₁₀ aryl, Y is C₁-C₃ alkylene;

as a reactive diluent in a process for polymerizing a curable composition comprising at least one polymerizable species, the process comprising the steps of providing the curable composition, mixing the curable composition with the reactive diluent, and polymerizing the mixture to form a crosslinked polymer,

wherein the curable composition comprises at least one photopolymerization initiator and is irradiated to initiate polymerization in the polymerization step, wherein the curable composition is heated to a predetermined elevated process temperature in the range of 90° C. to 120° C. before being irradiated with light having a suitable wavelength to be absorbed by the photoinitiator, thereby causing cleavage of the photoinitiator to induce polymerization of the curable composition to obtain the crosslinked polymer;

wherein the (meth)acryloyloxy-substituted benzoic acid ester is a 2- or 3-substituted benzoic acid ester having the (meth)acryloyloxy substituted at a meta- or ortho-position of the benzoic acid ester;

wherein the C₁-C₆ alkyl groups comprise linear, branched and cyclic alkyl groups;

wherein the C₁-C₃ alkylene groups comprise linear, branched and cyclic alkylene groups; and

wherein the process for polymerizing the curable composition is part of a 3D printing process.