The diamine composition according to an embodiment of the present invention comprises a benzylmonoamine having a methyl group in an amount of 10 ppm to 2,000 ppm in the composition. When it is used for the preparation of a diisocyanate composition and an optical material, it is possible to improve the optical characteristics by preventing the occurrence of yellowing, striae, and cloudiness in the optical material and enhancing the mechanical properties such as impact resistance at the same time. Thus, the diisocyanate composition can be applied to the preparation of a plastic optical lens of high quality.

A method of producing a polyamine compound, the method including: a first step of generating a polyurea compound by reacting a thiourethane resin and an amine compound A with each other; and a second step of generating a polyamine compound by reacting the polyurea compound and an amine compound B with each other.

A method of producing a polyamine compound, the method including: a first step of generating a polyurea compound by reacting a thiourethane resin and an amine compound A with each other; and a second step of generating a polyamine compound by reacting the polyurea compound and an amine compound B with each other.

A method of producing a thiourethane resin raw material, the method including comprising the step of generating the thiourethane resin raw material by reacting a thiourethane resin and an active hydrogen compound with each other.

A method of producing a thiourethane resin raw material, the method including comprising the step of generating the thiourethane resin raw material by reacting a thiourethane resin and an active hydrogen compound with each other.

A method of producing a thiourethane resin raw material, the method including comprising the step of generating the thiourethane resin raw material by reacting a thiourethane resin and an active hydrogen compound with each other.

The invention relates to a method for the preparation of isocyanates. Here it is provided that (i) a first organosilicon compound having at least one silicon atom Si.sup.1 and a unit of formula G-I bound thereto ##STR00001## is converted to a third organosilicon compound having a unit of formula G-II ##STR00002## by silylation of the NH group of the unit of formula G-I with a second organosilicon compound having one silicon atom Si.sup.2; and (ii) the third organosilicon compound is reacted to an isocyanate by thermolysis, whereby the unit of formula G-II is converted to an isocyanate group.

The invention relates to a method for the preparation of isocyanates. Here it is provided that (i) a first organosilicon compound having at least one silicon atom Si.sup.1 and a unit of formula G-I bound thereto ##STR00001## is converted to a third organosilicon compound having a unit of formula G-II ##STR00002## by silylation of the NH group of the unit of formula G-I with a second organosilicon compound having one silicon atom Si.sup.2; and (ii) the third organosilicon compound is reacted to an isocyanate by thermolysis, whereby the unit of formula G-II is converted to an isocyanate group.

A method of producing a thiourethane resin raw material, the method including comprising the step of generating the thiourethane resin raw material by reacting a thiourethane resin and an active hydrogen compound with each other.

A method of producing a thiourethane resin raw material, the method including comprising the step of generating the thiourethane resin raw material by reacting a thiourethane resin and an active hydrogen compound with each other.