The present invention is directed to a novel method of preparing a polymerizate, which includes the step of polymerizing a two-component composition, which includes: a first component containing at least one polycyanate reactant having at least two functional groups selected from isocyanate, isothiocyanate and combinations thereof, the polycyanate reactant being the reaction product of: a polythiol monomer having at least two thiol groups; and a polycyanate monomer having at least two functional groups selected from isocyanate, isothiocyanate and combinations thereof; and a second component containing at least one polyamine reactant having at least two functional groups selected from primary amine, secondary amine and combinations thereof. The molar equivalent ratio of (NCO+NCS) groups from the first component to (--NH.sub.2+--NH--) groups from the second component is from 0.5 to 100. The present invention is also directed to polymerizates prepared according to the method of the present invention. The present invention is further directed to photochromic articles that may be prepared from the polymerizates of the present invention.