A method of three-dimensional stereolithography printing a thiourethane polymer part using the vat resin. Adding a resin to a vat of a three-dimensional stereolithography printer, the resin a liquid mixture including: a first type of monomer including two or more thiol functional groups, a second type of monomer including two or more isocyanate functional groups, a photolatent base, an anionic step-growth polymerization reaction inhibitor and a light absorber. The photolatent base is decomposable upon exposure to a light to form a non-nucleophillic base catalyst having a pKa greater than 7. The anionic step-growth polymerization reaction inhibitor has an acidic group configured to form an acid-base pair with the non-nucleophillic base. The light absorber has an absorbance in the liquid mixture that is greater than an absorbance of the photolatent base at a wavelength of the light used for the exposure.