Abstract: A batch process for preparing a molded optical article includes introducing (i) a dithiol component or (ii) a polyisocyanate component into a reaction vessel; adding a first catalyst of organotin halide to form a first reaction mixture; heating the first reaction mixture; introducing a second catalyst of tertiary amine to the first reaction mixture; mixing a polyisocyanate (ii) into the reaction vessel containing the first reaction mixture if dithiol (i) was first added, or mixing a dithiol (i) into the first reaction mixture if the polyisocyanate (ii) was first added, to form a second reaction mixture; filling a mold with the second reaction mixture to provide a filled mold to form a molded optical article. The molar ratio of elemental tin present in the first catalyst to tertiary amine compound present in the second catalyst ranges from 0.04:1 to 0.29:1.