| abstract |
A process for preparing a thermoplastic thiourethane-urethane copolymer for optical use, which is a polymeric material which has a good balance between refractive index and Abbe number and possesses various properties required of optical products such as lenses. This process comprises the first step of reacting a diisocyanate and/or a diisothiocyanate with a thiol compound having two groups reactive with an isocyanate group, at least one of the reactive groups being an SH group, to prepare a thiourethane prepolymer having a weight-average molecular weight of 1 ,000 to 30,000; and the second step of reacting the thiourethane prepolymer prepared in the first step with a diisocyanate arid a hydroxyl-containing monomer having two groups reactive with an isocyanate group, at least one of the reactive groups being an OH group. |