Provided is a thioepoxide functional polymerizable composition comprising a reaction product of thiourea and an epoxide functional, polymerizable composition. The epoxide functional, polymerizable composition comprises a reaction product prepared from a reaction mixture comprising: (a) a monomer comprising at least one ethylenically unsaturated ester functional monomer having an epoxide functional group; and (b) a compound having two or more thiol groups. The reactants (a) and (b) are reacted via a Michael addition reaction in the presence of a base to form an epoxide functional reaction product. Also provided are methods of preparing an optical article using the polymerizable compositions.