Describes a method of preparing a polymerizate by polymerizing a two-component organic composition comprising: a first component containing a polyfunctional reactant having two or more functional groups selected from isocyanate, isothiocyanate and combinations of isocyanate and isothiocyanate groups; and a second component containing a polythiol represented by the following general formula I, ##STR1## wherein R.sub.1 and R.sub.2 are each selected from the group consisting of straight or branched chain alkylene, e.g., methylene and ethylene, cyclic alkylene, phenylene and C.sub.1 -C.sub.9 alkyl substituted phenylene. The second component may also optionally contain a reactive hydrogen compound that is different than the polythiol of general formula I. Polymerizates prepared according to the present invention are useful as ophthalmic lenses and have a refractive index of at least 1.57, an Abbe number of at least 33 and an initial Barcol hardness of at least 1. Also described are photochromic articles prepared from such polymerizates.