METHOD OF CURING A POLYTHIOURETHANE-BASED SUBSTRATE FROM A PRE-POLYMER

The invention relates to a method of curing a polythiourethane-based transparent casted substrate, comprising the steps of providing a first component A comprising a polythiourethane pre-polymer having iso(thio)cyanate end groups, said pre-polymer having been prepared from at least one polythiol monomer and at least one polyiso(thio)cyanate monomer, used in amounts adapted so that the molar ratio R2 of NCX/SH groups ranges from 2 to 35, providing a second component B comprising at least one polythiol monomer, mixing together first and second components A and B and filling a molding cavity with the resulting polymerizable mixture, curing said polymerizable mixture to obtain a polythiourethane-based transparent substrate, wherein said pre-polymer has been prepared by mixing said at least one polyiso(thio)cyanate monomer and said at least one polythiol monomer in initial amounts such that the initial molar ratio R1 of NCX/SH groups for said monomers ranges from 0.3 R2 to 0.95 R2, polymerizing the mixture, and adding to the mixture an additional amount of at least one polyiso(thio)cyanate monomer such that the molar ratio of NCX/SH groups for all the monomers used in the preparation of said pre-polymer is equal to R2, X being O or S.