Super-high refractive index optical resin composition having a higher heat deflection temperature and an excellent thermal stability, optical lens using it and its preparation method

A monomer composition for plastic optical lens is provided to ensure excellent lightness, excellent plasticity, dyeability, transparency, shock resistance, and high initial heat deflection temperature and to reduce central deformation of the lens and cracking of the multi-film of the lens due to heat. A monomer composition for plastic optical comprises (i) a compound 25~65 weight% where one or at least two selected from an alkylene diisocyanate compound, alicyclic diisocyanate compound, heterocyclic diisocyanate compound, and sulfur-containing aliphatic diisocyanate compound are added to tolylene diisocyanate, (ii) at least one or two mercapto compounds having at least one sulfur atom in one molecule, and (iii) a UV-absorbing agent, a release agent and a polymerization initiator. The monomer composition for plastic optical has 1.00~1.30 equivalence ratio of - SH (and, -OH) / -NCO, 1.550~1.660 liquid-phase refractive index (Ne,20 ‹C), 1.630~1.685 solid-phase refractive index (Ne, 20 ‹C), 24~50 Abbe's number(20 ‹C), and 10~1,000 cps of liquid viscosity(20 ‹C).