Latent borate-ammonium or iminium salts as photo-activatable catalysts for polythiourethane based substrates

Abstract

The present invention relates to a method of fast curing a polythiourethane based transparent substrate, comprising in one of its embodiments providing a first component (A) comprising a polythiourethane pre-polymer (A1) having isocyanate or isothiocyanate end groups, providing a second component (B) comprising a polythiourethane pre-polymer (B1) having thiol end groups, mixing together first and second components (A) and (B) to form a polymerizable mixture, curing said mixture to obtain a transparent substrate, wherein at least one photo-activatable latent catalyst composed of a quaternary ammonium or quaternary iminium cation and a borate anion is added in the process prior to the curing step, and said latent catalyst is subsequently photo- activated to carry out a polymerization reaction forming the polythiourethane-based transparent substrate.

Description

[0001] Latent borate-ammonium or iminium salts as photo-activatable catalysts for polythiourethane based substrates

[0002] The present invention relates to a process for manufacturing polythiourethane based substrates, and in particular optical substrates such as ophthalmic lenses, having generally a middle or high refractive index, preferably of at least 1 .52, more preferably of at least 1 .54, more preferably of at least 1 .6 and even more preferably of at least 1 .67, within short curing cycles using a latent photo-activatable catalyst, polymerizable compositions that can be used in such a process, and new latent photo-activatable catalysts.

[0003] BACKGROUND AND SUMMARY OF THE INVENTION

[0004] Ophthalmic lenses made of polythiourethane based substrates are typically made by a process comprising mixing appropriate monomers in a tank, such as a mixture of a polyisocyanate and a polythiol, adding catalyst and additive, filling a molding cavity with this liquid mixture of monomers, polymerizing the monomer mixture and thereafter recovering the polymerized polythiourethane based substrate from the mold. The mixture is usually subjected to a thermal cycle in an oven, for a typical duration of 20 hours, as shorter thermal curing cycles can face incomplete polymerization especially for thick lenses.

[0005] It is known to reduce the time required to cure the polymerizable composition poured into mold assemblies by using oligomers rather than monomers. The monomers are first pre-reacted to form oligomers, then blended with a catalyst that provides a high overall reactivity in very small volume or even through in-line mixing equipment, then poured into mold assemblies that are subjected to a short polymerization cycle, typically few hours.

[0006] In this regard, US 2003 / 125410 discloses a method of fast curing polythiourethane transparent casted substrate, which comprises the steps of:

[0007] 1) Providing a first component A comprising a polythiourethane pre-polymer having isocyanate or isothiocyanate end groups,

[0008] 2) Providing a second component B comprising a polythiourethane pre-polymer having thiol end groups,

[0009] 3) Mixing together first and second components A and B and filling a molding cavity of a casting mold assembly with the resulting mixture,

[0010] 4) Curing said mixture to obtain a transparent solid substrate, in the presence of a catalyst to shorten the curing time of the polymerizable composition down to typically 2 hours.

[0011] A fast cure process is highly desirable over usual processes as the shorter residence time in the curing oven enables a dramatic productivity gain, complex and demanding lens geometries can be obtained in better yield as the final polymerizable mixture shrinkage is lower than that of mixture obtained directly from monomers, compatibility with the adhesive of tape used for mold assembly is better, and energy consumption during polymerization cycles is reduced. Provided that the viscosity is controlled, batch mixing of such mixtures is inherently safer than usual process from monomers, as part of the available bond forming energy has already been released during the oligomers formation (pre-polymerization), which limits formation of local heat points in the final polymerizable mixture.

[0012] In applications EP 3916470 and EP 3919967, a different approach for fast curing a polythiourethane optical material has been chosen, combining the use of monomers and prepolymers in the presence of a polymerization catalyst.

[0013] Polythiourethane synthesis can be catalyzed by a wide variety of bases or Lewis acids. When basic catalysts are selected, they activate the thiol by forming the corresponding thiolate anion which is the species that attacks the iso(thio)cyanate carbon atom (nucleophilic activation).

[0014] Known catalysts include dibutyltin dichloride, nitrogen containing heterocycles, amines, or a mixture of KSCN and 18-crown-6. However, in the presence of such catalysts, it is difficult to control the reaction rate. Once initiated, the reaction forming the polythiourethane network is very fast and the system is difficult to process due to the high reactivity of the species involved in the reaction. When all ingredients are mixed together, the viscosity of the mixture increases quickly as the ingredients react to form species with increased molecular weight, and a gel is obtained at room temperature in less than 10 minutes.

[0015] Consequently, a major technical problem of the fast cure process described in the prior art is the short pot life of the polymerizable mixture, leading to a huge constraint on m ixing / fi Hing step as only a short time is allowed to achieve highly intimate mixing of very viscous pre-polymers before gelling. The pot-life of a polymerizable composition comprising polyiso(thio)cyanate and polythiol monomers is also reduced due to the high reactivity of monomers at room temperature.

[0016] A polymerizable mixture having a longer pot life, i.e. , a longer time range before reaching a viscosity where it is not anymore handleable (mixing / filing), would thus be a great advantage to extend mixing time, especially critical as the mixture is highly viscous. In addition, such a mixture could be advantageously processed in batches, similarly to the usual process starting from monomers.

[0017] To reduce the speed of the reaction, latent catalysts, which release the active catalyst after the application of an external stimulus, have been proposed.

[0018] EP 0182203 describes a method for preparing a polyurethane product by the reaction of a polyisocyanate with a polyol in the presence of a catalyst system consisting essentially of a tertiary amine and 1 to 35 wt. %, based on the tertiary amine, of an organic acid salt of a quaternary ammonium compound having a N-hydroxyalkyl group. The catalyst is used to delay the initiation time.

[0019] European patent application n° 22305961.9 discloses a method of fast curing a polythiourethane based transparent casted substrate, usable for making optical articles such as ophthalmic lenses, which comprises the use of a latent catalyst that is heat-activatable to accelerate the polymerization reaction forming the substrate. The catalysts used in this application are nitrogen containing basic organic compounds blocked by isocyanates or salts of these compounds with benzoic acid.

[0020] WO 2023 / 063398 discloses another approach by using a photo-curable composition comprising a polyiso(thio)cyanate compound, a polythiol compound and a base generator for producing a transparent polythiourethane resin. The base generator is composed of a borate anion and various ammonium or iminium cations. The photo-curable composition is cured by irradiation with ultraviolet rays or visible light. By irradiating the base generator with light, a base can be generated and the polymerization reaction can proceed. However, the pot life of the polymerizable mixture still needs to be improved.

[0021] Other photo-base generator systems are disclosed in EP 3078717, EP 2980180, WO 2021 / 261498, WO 2006 / 030029, WO 2015 / 014381 , WO 98 / 38195 or the article Progress Polym. Sci. 34, 2009, 194-209.

[0022] Thus, the aim of the present invention is to provide a method of fast curing a polythiourethane based transparent substrate which remedies to the drawbacks of the prior art methods in terms of limited pot life of the polymerizable mixture.

[0023] Another object of the invention is to provide a method of fast curing polythiourethane based transparent substrates substantially free from optical defects, in particular free from bubbles and / or striations resulting from the polymerization process. Still other objects of the invention are to provide a method characterized by high conversion rates of the starting materials, delivering materials with good thermo-mechanical properties and / or low yellowness indexes.

[0024] The present inventors found that the reactivity of the polymerizable mixture could be minimized by using specific catalysts that are blended under an inactive form and display essentially no catalytic effect in the polymerizable mixture, while being subsequently triggered by light irradiation to photo-cure the composition and form the final polythiourethane based polymer. These photo-latent catalysts allow a better control of the curing initiation of the polymerizable mixture containing monomers and / or pre-polymers than traditionally used non-latent catalysts such as tin catalysts.

[0025] The present invention provides a process of curing a polythiourethane-based transparent substrate, usable for making optical articles such as ophthalmic lenses, comprising the following steps 1), 2), 3), 4) and 5), 1), 2’), 3), 4) and 5), T), 2), 3), 4) and 5) or T), 2’), 3), 4) and 5):

[0026] 1) Providing a first component A comprising at least one polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said prepolymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or

[0027] T) Providing a first component A comprising at least one polyisocyanate or polyisothiocyanate monomer A2,

[0028] 2) Providing a second component B comprising at least one polythiourethane pre-polymer B1 having thiol end groups, said pre-polymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or

[0029] 2’) Providing a second component B comprising at least one polythiol monomer B2, 3) Mixing together first and second components A and B to form a polymerizable mixture,

[0030] 4) Curing said polymerizable mixture to obtain a polythiourethane-based transparent substrate, and

[0031] 5) Recovering the polythiourethane-based transparent substrate, wherein at least one photo-activatable latent catalyst composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1b) is added in the process prior to curing step 4): in which Ra, Rb, Rcand Rdindependently represent a (hetero)aryl group or a substituted or unsubstituted alkyl group, R1represents an (hetero)aryl group, and:

[0032] - R2, R3and R4independently represent a substituted or unsubstituted alkyl group or a (hetero)aryl group, or

[0033] - R3represents a substituted or unsubstituted alkyl group or a (hetero)aryl group and R2and R4together form a divalent radical of formula -R2-R4-, or

[0034] - R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted unsaturated 5- or 6-member non-aromatic heterocyclic group, or

[0035] - R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted 5- or 6-member heteroaromatic group, or

[0036] - R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted saturated bicyclic group, and said latent catalyst is subsequently photo-activated to carry out a (photo-) polymerization reaction forming the polythiourethane-based transparent substrate.

[0037] In formula (1a), R2, R3and R4are not necessarily connected to the quaternary nitrogen atom by single bonds but two of them may together form a double bond.

[0038] The present process offers several advantages in addition to those mentioned above. The latent catalyst according to the invention allows a good control of the curing process, avoids premature gelling of the polymerizable mixture, while reaching a complete curing in a reduced time.

[0039] The polythiourethane materials obtained from polymerization catalyzed by the latent catalysts according to the invention have similar mechanical and thermal characteristics to the ones obtained by using the commonly used non-latent catalysts. The conversion levels obtained were higher.

[0040] The invention also relates to a polymerizable mixture comprising the above defined latent catalyst, which exhibits an improved processability and shelf life.

[0041] The reactivity of the finally formulated polymerizable mixture is essentially the same as that of an uncatalyzed blend, and it can be flowed through pipe to filling stations with less risks of clogging from local gelling. All components can be admixed together, including the catalyst, over a period of time that is compatible with a very high level of mixing state, reducing inhomogeneities and optical defects likeliness such as striations.

[0042] DETAILED DESCRIPTION OF THE INVENTION

[0043] The substrate of the invention is an organic glass substrate, made from a thermosetting resin. The polymer matrix of substrate is obtained from a photo-curable thiourethane composition (“substrate composition”) comprising monomers or at least one polymerizable pre-polymer, preferably at least two.

[0044] The substrate is preferably an optical article substrate, more preferably an optical lens substrate. The optical article is preferably an ophthalmic lens, such as a plastic eyeglass lens.

[0045] In the present description, unless otherwise specified, a substrate is understood to be transparent when the observation of an image through said substrate is perceived with no significant loss of contrast, that is, when the formation of an image through said substrate is obtained without adversely affecting the quality of the image. This definition of the term “transparent” can be applied to all objects qualified as such in the description, unless otherwise specified.

[0046] The term “ophthalmic lens” is used to mean a lens adapted to a spectacle frame to protect the eye and / or correct the sight. Said lens can be chosen from afocal, unifocal, bifocal, trifocal, progressive lenses and Fresnel lenses or any other kind of lenses having a discontinuous surface. Although ophthalmic optics is a preferred field of the invention, it will be understood that this invention can be applied to optical elements of other types such as, for example, lenses for optical instruments, filters particularly for photography or astronomy, optical sighting lenses, ocular visors, optics of lighting systems, screens, glazings, etc.

[0047] If the optical article is an optical lens, it may be coated on its front main surface, rear main side, or both sides with one or more functional coatings. As used herein, the rear face of the substrate is intended to mean the face which, when using the article, is the nearest to the wearer's eye. It is generally a concave face. On the contrary, the front face of the substrate is the face which, when using the article, is the most distant from the wearer's eye. It is generally a convex face. The optical article can also be a piano article.

[0048] A substrate, in the sense of the present invention, should be understood to mean an uncoated substrate, and generally has two main faces. The substrate may in particular be an optically transparent material having the shape of an optical article, for example an optical lens or an ophthalmic lens destined to be mounted in glasses. In this context, the term “substrate” is understood to mean the base constituent material of the optical lens and more particularly of the ophthalmic lens. This material may act as support for a stack of one or more coatings or layers.

[0049] The refractive index of the polythiourethane based transparent substrate is preferably 1.52 or greater, more preferably 1.54 or greater, more preferably 1.56 or greater, more preferably 1.58 or greater, more preferably 1.60 or greater, and still more preferably 1.65 or greater, and it is preferably 1.80 or less, more preferably 1.70 or less, and still more preferably 1.67 or less. Unless otherwise specified, the refractive indexes referred to in the present application are expressed at 25°C at a wavelength of 550 nm.

[0050] The fast cure polymerizable composition leading to a polythiourethane based material is composed of two main components.

[0051] In a first embodiment of the invention, the first component A is comprised of a polythiourethane pre-polymer A1 having isocyanate (NCO) or isothiocyanate (NCS) end groups. The second component B is comprised of a polythiourethane pre-polymer B1 having thiol (SH) end groups.

[0052] In step 1) of the present process, a first component A comprising a polythiourethane prepolymer A1 having isocyanate or isothiocyanate end groups is provided and has been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, the latter being used in excess. The first component A comprises therefore oligomers and the initial monomers that did not polymerize.

[0053] In step 2) of the present process, a second component B comprising a polythiourethane pre-polymer B1 having thiol end groups is provided and has been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, the former being used in excess. The second component B comprises therefore oligomers and the initial monomers that did not polymerize.

[0054] This first embodiment provides materials having the best performances in terms of thermomechanical properties, conversion rate, yellowness index and cosmetic appearance.

[0055] In a second embodiment of the invention, the first component A is comprised of a polythiourethane pre-polymer A1 having isocyanate (NCO) or isothiocyanate (NCS) end groups (step 1). The second component B is comprised of at least one polythiol monomer B2 (step 2’).

[0056] In a third embodiment of the invention, the first component A is comprised of at least one polyisocyanate or polyisothiocyanate monomer A2 (step T). The second component B is comprised of a polythiourethane pre-polymer B1 having thiol (SH) end groups (step 2).

[0057] In a fourth embodiment of the invention, the first component A is comprised of at least one polyisocyanate or polyisothiocyanate monomer A2 (step T). The second component B is comprised of at least one polythiol monomer B2 (step 2’).

[0058] The use of at least one pre-polymer in the polymerizable composition (embodiments 1-3) provides final materials with a lower yellowness index than polymerizable compositions containing only monomers (embodiment 4).

[0059] By pre-polymer, it is meant a polymer or oligomer comprising pre-polymer molecules. By pre-polymer molecule, it is meant a macromolecule or oligomer molecule capable of entering, through reactive (polymerizable) groups, into further polymerization, thereby contributing more than one monomeric unit to at least one chain of the final macromolecule. It is generally formed from two or more different monomers. The polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer and at least one polythiol monomer in a proportion such that the molar ratio of isocyanate or isothiocyanate groups to thiol groups NCX / SH preferably ranges from 3:1 to 30:1 , preferably in the absence of a catalyst, X being O or S.

[0060] The polythiourethane pre-polymer B1 having thiol end groups is prepared by reacting at least one polyisocyanate or polyisothiocyanate monomer and at least one polythiol monomer in a proportion such that the molar ratio of the thiol groups to the isocyanate or isothiocyanate groups SH / NCX preferably ranges from 3:1 to 30:1 , preferably in the absence of a catalyst, X being O or S.

[0061] Polythiol and polyisocyanate or polyisothiocyanate compounds used to prepare polythiourethane pre-polymer A1 or B1 are considered herein as monomers, even when they are oligomers.

[0062] By polyisocyanate, it is meant any compound comprising at least two isocyanate groups, in other words diisocyanates, triisocyanates, etc. Polyisocyanate pre-polymers may be used. The polyisocyanate may be any suitable polyisocyanate having two or more, preferably two or three isocyanate functions.

[0063] The polyisocyanates may be selected from aliphatic, aromatic, cycloaliphatic or heterocyclic polyisocyanates and mixtures thereof.

[0064] Polyisothiocyanate are defined in the same manner as polyisocyanates above, by replacing the “isocyanate” group by the “isothiocyanate” group.

[0065] The preferred polyisocyanate or isothiocyanate monomers are those having the formulae: wherein R1is independently H or a C1-C5 alkyl group, preferably CH3 or C2H5;

[0066] R2is H, a halogen, preferably Cl or Br, or a C1-C5 alkyl group, preferably CH3 or C2H5;

[0067] Z is -N=C=X, with X being O or S, preferably O; a is an integer ranging from 1 to 4, b is an integer ranging from 2 to 4 and a + b < 6; and x is an integer from 1 to 10, preferably 1 to 6. The polyisocyanates of the invention are preferably diisocyanates. Among the available diisocyanates may be cited toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, paraphenylene diisocyanate, xylylene diisocyanate, biphenyl-diisocyanate, 3,3'-dimethyl-4,4'-diphenylene diisocyanate, tetramethylene-1 ,4-diisocyanate, hexamethylene-1 ,6-diisocyanate, 2,2,4-trimethyl hexane-1 ,6-diisocyanate, lysine methyl ester diisocyanate, bis(isocyanatoethyl) fumarate, isophorone diisocyanate (IPDI), ethylene diisocyanate, dodecane-1 ,12-diisocyanate, cyclobutane-1 ,3-diisocyanate, cyclohexane-1 ,3-diisocyanate, cyclohexane-1 ,4-diisocyanate, methylcyclohexyl diisocyanate, hexahydrotoluene-2,4-diisocyanate, hexahydrotoluene-2,6- diisocyanate, hexahydrophenylene-1 ,3-diisocyanate, hexahydrophenylene-1 ,4-diisocyanate, perhydro diphenylmethane-2,4'-diisocyanate, perhydro phenylmethane-4,4'-diisocyanate (or bis- (4-isocyanatocyclohexyl)-methane, or 4,4'-dicyclohexylmethanediisocyanate), bis(isocyanatomethyl) cyclohexane, dicyclohexylmethane diisocyanate, 2,5(or 2,6)- bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, and their mixtures.

[0068] Other non-limiting examples of polyisocyanates are the isocyanurates from isophorone diisocyanate and 1 ,6-hexamethylene diisocyanate, both of which are commercially available. Further polyisocyanates suitable for the present invention are described in detail in WO 98 / 37115, WO 2014 / 133111 or EP 1877839.

[0069] The polythiols that may be used in the present invention are defined as compounds comprising at least two sulfhydryl (mercapto) groups, in other words dithiols, trithiols, tetrathiols etc. Polythiols pre-polymers may be used. The polythiol may be any suitable polythiol having two or more, preferably two or three thiol functions.

[0070] Among the preferred polythiol monomers and / or oligomers suitable in accordance with the present invention, there may be cited aliphatic polythiols such as trimethylolpropanetris(2- mercaptoacetate), trimethylolpropanetris(3-mercaptopropionate), trimethylolethanetris(2- mercaptoacetate), trimethylolethanetris(3-mercaptopropionate), pentaerythritol tetrakis(2- mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), bis(mercaptomethyl)sulfide, bis(mercaptomethyl)disulfide, bis(mercaptoethyl)sulfide, bis(mercaptoethyl)disulfide, bis(mercaptopropyl)sulfide, bis(mercaptopropyl)disulfide, 2,3-bis((2-mercaptoethyl)thio)-1- propanethiol, 4,8(or 4,7 or 5,7)-dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 2,5- dimercaptomethyl-1 ,4-dithiane, and 2,5-bis[(2-mercaptoethyl)thiomethyl]-1 ,4-dithiane, mercaptoethylthio)-2,3-dimercaptopropane, 1-(2’-mercapropylthio)-2,3-dimercaptopropane, 1- (3’-mercapropylthio)-2,3-dimercaptopropane, 1-(4’-mercabutylthio)-2,3-dimercaptopropane, 1- (5’-mercapentylthio)-2,3-dimercaptopropane, 1-(6’-mercahexylthio)-2,3-dimercaptopropane, 1 ,2- bis-(4’-mercaptobutylthio)-3-mercaptopropane, 1 ,2-bis-(5’-mercaptopentylthio)-3- mercaptopropane, 1 ,2-bis-(6’-mercaptohexylthio)-3-mercaptopropane, 1 ,2,3- tris(mercaptomethylthio)propane, 1 ,2,3-tris-(3’-mercaptopropylthio)propane, 1 ,2 , 3-tris-(2’- mercaptoethylthio)propane, 1 ,2,3-tris-(4’-mercaptobutylthio)propane, 1 ,2 , 3-tris-(6’- mercaptohexylthio)propane, methanedithiol, 1 ,2-ethanedithiol, 1 ,1 -propanedithiol, 1 ,2- propanedithiol, 1 ,3-propanedithiol, 2,2-propanedithiol, 1 ,6-hexanethiol-1 ,2,3-propanetrithiol, and 1 ,2-bis(2’-mercaptoethylthio)-3-mercaptopropane. Further examples of polythiols are shown in the formulae below or can be found in WO 2014 / 133111 , EP 394495, US 4775733 or EP

[0071] 1877839:

[0072] C2H5C(CH2COOCH2CH2SH)3

[0073] Preferred embodiments are combination of xylylene diisocyanate and pentaerythritol tetrakis(3-mercaptopropionate); combination of xylylene diisocyanate and 2,3-bis((2- mercaptoethyl)thio)-1 -propanethiol; combination of 2,5 (or 2,6)-bis(isocyanatomethyl)bicyclo- [2.2.1]-heptane, pentaerythritol tetrakis(3-mercaptopropionate) and 2,3-bis((2- mercaptoethyl)thio)-1-propanethiol; combination of xylylene diisocyanate and 4,8(or 4,7 or 5,7)- dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane; combination of dicyclohexylmethane diisocyanate and 4,8(or 4,7 or 5,7)-dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane; or a combination of bis(2,3-epithiopropyl)disulfide and 4,8(or 4,7 or 5,7)-dimercaptomethyl-1 ,11- dimercapto-3,6,9-trithiaundecane. The most preferred polythiol is 2,3-bis((2-mercaptoethyl)thio)- 1 -propanethiol, shown below:

[0074] Preferably the polythiols have a viscosity at 25°C of 1 Pa.s or less, more preferably 5.10’1Pa.s or less, more preferably 2.5.1 O'1Pa.s or less, more preferably 2.1 O'1Pa.s or less, more preferably 10'1Pa.s or less and even more preferably of 0.5.1 O'1Pa.s or less.

[0075] Depending on the embodiment of the invention, components A and B are prepared by polymerizing mixtures of required amounts of at least one polyisocyanate and / or at least one polyisothiocyanate monomer and at least one polythiol monomer (steps 1 and 2), and optionally polyols monomers, hydroxy-thiol monomers and / or polyamines monomers. Typically, components A and B can be prepared through classical thermal polymerization including induction and infrared heating.

[0076] The amounts of polyisocyanate or polyisothiocyanate monomers and polythiol monomers in the reaction medium are preferably adapted in each case in such a way that the molar ratio of NCX / SH groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane pre-polymer A1 , preferably from 6:1 to 10:1 , and / or the molar ratio of SH / NCX groups for the mixture of polyisocyanate or polyisothiocyanate monomers and polythiol monomers ranges from 3:1 to 30:1 for the preparation of polythiourethane pre-polymer B1 , preferably from 6: 1 to 10: 1 , X being O or S.

[0077] In one embodiment, both components A and B are prepared without the use of a catalyst system, which allows better control of the polymerization reaction and results in pre-polymers of high stability in time. However, they can be prepared using a catalyst or catalyst system as described above.

[0078] Generally, in the first embodiment of the invention, the at least one pre-polymer A1 and the at least one pre-polymer B1 are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0079] Generally, in the second embodiment of the invention, the at least one pre-polymer A1 and the at least one polythiol monomer are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0080] Generally, in the third embodiment of the invention, the at least one polyisocyanate or polyisothiocyanate monomer and the at least one pre-polymer B1 are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1 .2, preferably 1.

[0081] Generally, in the fourth embodiment of the invention, the at least one polyisocyanate or polyisothiocyanate monomer and the at least one polythiol monomer are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1 .2, preferably 1.

[0082] Generally, in the second embodiment of the invention, the pre-polymer A1 and the polythiol of component B are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0083] Generally, in the third embodiment of the invention, the polyisocyanate or polyisothiocyanate of component A and the pre-polymer B1 are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0084] Generally, in the fourth embodiment of the invention, the polyisocyanate or polyisothiocyanate of component A and the polythiol of component B are comprised in the mixture in an amount such that the molar ratio of NCX to SH groups is from 0.8 to 1.2, preferably 1.

[0085] Preparation of pre-polymer B1 having thiol end groups has already been described in US 5908876. Similar process can be used to prepare component B of the present invention. When component A of the present invention comprises polythiourethane pre-polymer A1 , it can be prepared in a similar manner but with the required ratio of polyisocyanate or polyisothiocyanate and polythiol monomers in order to obtain polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups.

[0086] In one embodiment, the polythiourethane pre-polymer A1 and / or B1 is prepared by directly blending the total amount of the two monomers (the at least one polyisocyanate or polyisothiocyanate monomer and the at least one polythiol monomer) and subjecting the overall mixture to a thermal treatment to enable the pre-polymer formation. Stated otherwise, in this embodiment, the polythiourethane pre-polymer is directly prepared by mixing the at least one polyisocyanate or polyisothiocyanate monomer and the at least one polythiol monomer at the desired ratio.

[0087] In another embodiment, the polythiourethane pre-polymer A1 and / or B1 is prepared by firstly blending the minor monomer with a part of the major monomer, secondly subjecting this mixture to a thermal polymerization treatment to enable oligomer formation, and thirdly diluting this concentrated mixture with the remaining part of major monomer. This way of proceeding generally leads to an improvement of the thermal properties of the final polythiourethane polymer.

[0088] The mixture polythiol / polyiso(thio)cyanate from which pre-polymer A1 is obtained may comprise 90% or less by weight of at least one polyol. Preferably, said mixture may comprise 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less by weight of at least one polyol. Also preferably, no polyol is used. Polyiso(thio)cyanate means polyisocyanate or polyisothiocyanate.

[0089] The mixture polythiol / polyiso(thio)cyanate from which pre-polymer B1 is obtained may comprise 90% or less by weight of at least one polyol. Preferably, said mixture may comprise 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less by weight of at least one polyol. Also preferably, no polyol is used.

[0090] The mixture of components A and B according to the invention may also include additives which are conventionally employed in polymerizable compositions intended for molding optical articles, in particular ophthalmic lenses, in conventional proportions, namely inhibitors, dyes, photochromic agents, UV absorbers, perfumes, deodorants, antioxidants, resin modifiers, color balancing agents, chain extenders, crosslinking agents, free radical scavengers such as antioxidants or hindered amine light stabilizers (HALS), dyes, pigments, fillers, adhesion accelerators, anti-yellowing agents, photosensitizers and mold release agents.

[0091] In one embodiment, the additives are added to first component A prior to the mixing with second component B.

[0092] UV absorbers are frequently incorporated into optical articles in order to reduce or prevent UV light from reaching the retina (in particular in ophthalmic lens materials). The UV absorber that may be used in the present invention preferably have the ability to at least partially block light having a wavelength shorter than 400 nm, but can also have an absorption spectrum extending to the visible blue light range of the electromagnetic spectrum (400 - 450 nm), in particular 400- 430 nm.

[0093] Said UV absorbers both protect the user’s eye from UV light and the substrate material itself, thus preventing it from weathering and becoming brittle and / or yellow. The UV absorber according to the invention can be, without limitation, a benzophenone-based compound, a benzotriazole-based compound or a dibenzoylmethane-based compound, preferably a benzotriazole compound. Suitable UV absorbers include without limitation 2-(2-hydroxyphenyl)- benzotriazoles such as 2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-5-chlorobenzotriazole (Seesorb® 703 I Tinuvin® 326), or other allyl hydroxymethylphenyl chlorobenzotriazoles, 2-(5- chloro-2H-benzotriazol-2-yl)-6-(1 ,1-dimethylethyl)-4-methylphenol (Viosorb® 550), n-octyl-3-[3- tert-butyl-4-hydroxy-5-(5-chloro-2H-benzotriazol-2-yl)phenyl] propionate (Eversorb® 109), 2-(2- hydroxy-5-methoxyphenyl)benzotriazole, 2-(2-hydroxy-5-butoxyphenyl)benzotriazole and also Tinuvin®CarboProtect® from BASF. Preferred absorbers are of the benzotriazole family. Other examples of benzotriazole UV absorbers protecting from blue light can be found in WO 2017 / 137372.

[0094] The amount of UV absorber compounds according to the invention used herein is an amount sufficient to provide a satisfactory protection from UV light but not excessive so as to prevent precipitation. The UV absorber compounds are preferably present in a low amount to avoid the inhibition of the photopolymerization.

[0095] Among the release agents that may be used in the invention, there may be cited mono and dialkyl phosphates, alkyl ester phosphates, silicones, fluorinated hydrocarbon, fatty acids and ammonium salts. The preferred release agents are mono and dialkyl phosphates, alkyl ester phosphates and mixtures thereof. Such release agents are disclosed inter alia in US 4975 328 and EP 271839. The release agent is preferably used in an amount lower than or equal to 1% by weight based on the total weight of the polymerizable compounds present in the mixture of components A and B.

[0096] The polymerizable mixture of the present invention can comprise a solvent for promoting the dissolution of the catalyst, which is under the form of a salt.

[0097] Any polar organic solvent can be used such as acetonitrile, tetra hydrofuran, dioxane, ethanol, thioethanol, acetone, and 3-methyl-2-butene-1-ol. The amount of solvent is generally kept below 2% by weight, based on the total weight of the polymerizable compounds present in the mixture of components A and B and preferably from 0 to 0.5% by weight, to avoid haze and bubbling.

[0098] In the present invention, at least one latent catalyst according to the invention that is photo- activatable is added in the process prior to curing step 4), and said latent catalyst is subsequently photo-activated to carry out a polymerization reaction forming the polythiourethane based transparent substrate.

[0099] The catalyst is a system for accelerating the polymerization reaction. The catalyst used in the present process can comprise one or more latent photo-activatable catalysts and preferably only comprises latent photo-activatable catalysts according to the invention, i.e., composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1 b). The catalyst used in the present process is in fact a pre-catalyst that leads to the active form of the catalyst upon activation by irradiation.

[0100] The catalyst shall be used in the polymerizable composition in an effective amount, i.e., an amount sufficient to promote the polymerization of the mixture. Generally, the at least one catalyst is used in a proportion of 0.01 to 5% by weight with respect to the total weight of polymerizable compounds present in the mixture of components A and B, more preferably from 0.02 to 2% or 0.04 to 1%.

[0101] As used herein, a latent catalyst, or blocked / triggerable catalyst, is a catalyst that displays a delayed action. The latent catalyst will not display a significant catalytic effect, i.e., will not significantly react with active SH, NCO and / or NCX groups until activated. In the present invention, the latent catalyst is activated by irradiation with an appropriate light source. Depending on its nature, it can also be activated by heat.

[0102] The latent catalyst according to the invention generally provides the polymerizable composition with a pot life that is significantly greater than the pot life provided by conventional latent or non-latent catalysts or the pot life provided by said latent catalyst once activated. For example, said pot life is of 8 hours or more or 12 hours or more and is preferably of 1 day or more. The pot life is the time during which a fully formulated polymerizable composition has a viscosity such that it is pourable, e.g., processable (typically filling in the assemblies).

[0103] The latent catalyst is generally activated during curing step 4), preferably photo-activated during curing step 4). If the latent catalyst was activated during the mixing step 3), the pot life of the mixture would be shortened. The mixture could become too viscous too soon and the molds might not be filed properly.

[0104] The latent catalyst that is photo-activatable is activated by visible and / or UV radiation, preferably UV radiation. This can be done at room temperature (20-25°C). In one embodiment, the activation of the latent catalyst is carried out without heating. It is generally inactive at room temperature, even at higher temperatures, and will not significantly react until activated by irradiation.

[0105] The latent catalyst can be added at different stages of the present process.

[0106] In one embodiment, the catalyst is added to the polythiol and polyisocyanate or polyisothiocyanate monomers during the preparation of the polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups or to the polythiol and polyisocyanate or polyisothiocyanate monomers during the preparation of the polythiourethane pre-polymer B1 having thiol end groups, or to the polyisocyanate or polyisothiocyanate monomers during the preparation of component A, or to the polythiol monomers during the preparation of component B, depending on the case.

[0107] In a preferred embodiment, the catalyst is added to the first component A obtained in step 1) or T) prior to mixture with component B or to the second component B obtained in step 2) or 2’) prior to mixture with component A. In the embodiment where step 1) and / or step 2) is carried out, the catalyst is added to pre-polymers A1 and / or B1 after their preparation, depending on the case.

[0108] In another preferred embodiment, the catalyst is added to the mixture of components A and B in step 3) of the present process.

[0109] The photo-activatable latent catalyst according to the invention is composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1 b): in which Ra, Rb, Rcand Rdindependently represent a (hetero)aryl group or a substituted or unsubstituted alkyl group, R1represents an (hetero)aryl group, and R2, R3and R4define five families of compounds (1a) that will be defined.

[0110] By ammonium cation, it is meant a cation having a positively charged nitrogen atom (N+) with only univalent groups bonded to said nitrogen atom. A quaternary ammonium cation derives from the parent NH4+cation by substitution of all four hydrogen atoms with four univalent groups.

[0111] By iminium cation, it is meant a cation that includes a carbon-nitrogen double bond with the structure C=N+. A quaternary iminium cation has a positively charged nitrogen atom involved in a carbon-nitrogen double bond and said positively charged nitrogen atom bears two univalent groups different from a hydrogen atom, in at least one of its mesomeric forms. The latter structure can be part of an aromatic ring. Examples of iminium compounds include guanidinium, amidinium, pyridinium, pyrazolium and imidazolium compounds.

[0112] The quaternary ammonium or iminium cations have no hydrogen atom on the positively charged nitrogen atom shown on formula (1a). The non-hydrogen groups born by the positively charged nitrogen atom are preferably connected through a carbon atom.

[0113] In the present application, the term "alkyl" denotes a linear or branched, cyclic or acyclic, saturated or unsaturated hydrocarbon-based radical connected to the rest of the molecule via an sp3carbon atom, containing preferably from 1 to 25 carbon atoms, especially including acyclic groups containing from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl and n-hexyl groups, cycloalkyl groups preferably containing from 3 to 7 carbon atoms, cycloalkylmethyl groups preferably containing from 4 to 8 carbon atoms.

[0114] By "substituted alkyl" is understood an alkyl group as defined above, connected to the rest of the molecule via an sp3carbon atom and in which one or more methylene hydrogen atoms are replaced with a substituent. The substituted alkyl group can be substituted by one or a plurality of aryl groups and / or one or a plurality of heteroatoms such as N, S, O or a halogen atom (fluorine, chlorine, bromine or iodine). Mention will be made by way of examples of arylalkyl groups (alkyl group substituted with at least one aryl group) such as the trityl group (-CPha), the benzyl group or the 4-methoxybenzyl group, alkoxyalkyl groups, such as the methoxymethyl group or dialkoxymethyl groups such as the diethoxymethyl or dimethoxymethyl groups, the groups CH2CO2R11, wherein R11represents an optionally substituted alkyl or aryl group.

[0115] The term "aryl" denotes an aromatic monovalent carbocyclic radical, connected by an sp2carbon atom, including a single ring (for example a phenyl group) or multiple condensed rings (for example the naphthyl, terphenyl groups), which may optionally be substituted by one or a plurality of groups such as, without limitation, alkyl (for example methyl), hydroxyalkyl, aminoalkyl, hydroxyl, thiol, amino, halogeno (fluoro, bromo, iodo, chloro), nitro, alkylthio, alkoxy (for example methoxy), aryloxy, mono-alkylamino, dialkylamino, acyl, carboxyl, alkoxycarbonyl, aryloxycarbonyl, hydroxysulphonyl, alkoxysulphonyl, aryloxysulphonyl, alkylsulphonyl, alkylsulphinyl, cyano, trifluoromethyl, tetrazolyl, carbamoyl, alkylcarbamoyl, dialkylcarbamoyl groups. Alternatively, two adjacent positions of the aromatic ring may be substituted by a methylenedioxyl or ethylenedioxyl group. The aryl group preferably comprises from 6 to 18 carbon atoms.

[0116] The term "heteroaryl" denotes an aryl group as defined above, connected to the rest of the molecule via an sp2carbon atom, wherein one or a plurality of carbon atoms of the aromatic ring(s) have been replaced with a heteroatom such as nitrogen, oxygen, phosphorus, or sulfur. The heteroaryl groups may be structures with a single or a plurality of aromatic rings, or structures with a single or a plurality of aromatic rings coupled with one or a plurality of non-aromatic rings. In the structures having a plurality of rings, the rings may be fused, bonded covalently or bonded together via a divalent common group such as a methylene, ethylene, carbonyl group. Examples of heteroaryl groups are the thiophene (2-thienyl, 3-thienyl), pyridine (2-pyridyl, 3-pyridyl, 4- pyridyl), isoxazole, phthalimide, pyrazole, indole, furan groups and the benzofused analogues thereof, phenyl pyridyl ketone, quinoline, phenothiazine, carbazole, benzopyranone.

[0117] A (hetero)aryl group represents a heteroaryl or aryl group.

[0118] The suffix “-ene” is used to describe a divalent group. Thus, any of the monovalent groups defined herein can be modified with the suffix “-ene” to describe a divalent version of that moiety. For example, a divalent alkyl group is “alkylene”. Alkylene groups are connected to the rest of the molecule via two sp3carbon atoms.

[0119] In the present application, alkyl groups preferably comprise from 1 to 6 carbon atoms, more preferably from 1 to 4 carbon atoms, from 1 to 3 carbon atoms, or from 1 to 2 carbon atoms.

[0120] In formula (1a), R1preferably represents a (hetero)aryl group having preferably from 6 to 18 carbon atoms, more preferably an aryl group having preferably from 6 to 18 carbon atoms. Examples of suitable R1groups include phenyl, substituted or unsubstituted naphthyl, substituted or unsubstituted anthracenyl, substituted or unsubstituted phenanthryl, more preferably substituted or unsubstituted 2-naphthyl. These embodiments of the R1group are valid for all quaternary ammonium or quaternary iminium cations mentioned in the present application.

[0121] The first family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises compounds in which R2, R3and R4independently represent a substituted or unsubstituted alkyl group or a (hetero)aryl group. R2, R3and R4preferably represent identical or different alkyl groups.

[0122] Preferred combinations for this first family include R2= R3= R4= ethyl (generating the active catalyst triethylamine), R2= R3= R4= -CH2CH2OH (generating the active catalyst triethanolamine), R2= R3= R4= butyl (generating the active catalyst tributylamine), preferably n- butyl, R2= R3= isopropyl and R4= ethyl (generating the active catalyst N,N- diisopropylethylamine), R2= R3= methyl and R4= cyclohexyl (generating the active catalyst N,N- dimethylcyclohexylamine). Some preferred structures corresponding to the first family of compounds (1a) are shown hereunder:

[0123] The second family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises compounds in which R3represents a substituted or unsubstituted alkyl group or a (hetero)aryl group (preferably a substituted or unsubstituted alkyl group such as methyl or ethyl) and R2and R4together form a divalent radical of formula -R2-R4-. In other words, R2and R4are bonded to each other to form a ring structure.

[0124] The divalent radical of formula -R2-R4- defined in the present application is preferably saturated. It comprises carbon atoms and optionally heteroatoms such as oxygen, nitrogen and sulfur in its main chain. Said main chain preferably contains 4 to 6 atoms. The divalent radical of formula -R2-R4- preferably represents a substituted or unsubstituted alkylene group, preferably a linear alkylene group of formula (CH2)P, with p being an integer ranging from 4 to 6, preferably from 4 to 5, or a group of formula -CH2CH2OCH2CH2-, or a group of formula - CH2CH2NR15CH2CH2-, R15representing a (hetero)aryl group or a substituted or unsubstituted alkyl group.

[0125] Preferred combinations for this first family include R3= methyl and -R2-R4- = - CH2CH2OCH2CH2- (generating the active catalyst N-methylmorpholine), R3= methyl and -R2-R4- = (CH2)S (generating the active catalyst N-methylpiperidine).

[0126] Some preferred structures corresponding to the second family of compounds (1a) are shown hereunder:

[0127] The third family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises compounds in which R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted unsaturated 5- or 6-member non-aromatic heterocyclic group. Examples of such iminium compounds have formula (3): in which Q represents an alkylene group of formula (CH2)m, m being 2 or 3, R1arepresents a (hetero)aryl group, a substituted or unsubstituted alkyl group and R4arepresents a hydrogen atom, a (hetero)aryl group, a substituted or unsubstituted alkyl group or R1aand R4atogether form a saturated divalent radical of formula -R1-R4-.

[0128] The saturated divalent radical of formula -R1a-R4a- defined in the present application comprises carbon atoms and optionally heteroatoms such as oxygen, nitrogen and sulfur in its main chain. Said main chain preferably contains 3 to 5 atoms. The saturated divalent radical of formula -R1a-R4a- preferably represents a substituted or unsubstituted alkylene group, preferably a linear alkylene group of formula (CH2)P, with p being an integer ranging from 3 to 5, preferably from 3 to 4, or a group of formula -CHR6CHR7CHR8NR5- in which R5represents a (hetero)aryl group, a substituted or unsubstituted alkyl group, R6, R7and R8independently represent a hydrogen atom, a (hetero)aryl group, a substituted or unsubstituted alkyl group, the nitrogen atom of the main chain of this group being connected to the cyclic carbon atom in the compound of formula (3). This group is preferably a group of formula -CH2CH2CH2NR5- in which R5is as defined previously and preferably represents an alkyl group.

[0129] In one embodiment of the invention, Q in the compound of formula (3) is an alkylene group of formula (CH2)m, m being 2 or 3, preferably 3, and R1aand R4atogether form a saturated divalent radical of formula -R1a-R4a- representing a substituted or unsubstituted alkylene group. A preferred family of such amidinium compounds has formula (3a): in which n represents an integer ranging from 1 to 3 and R9an R10independently represent hydrogen, a substituted or unsubstituted alkyl group or a (hetero)aryl group.

[0130] A preferred family of tertiary iminium cations of formula (3a) includes iminium compounds of formula (4), in which n represents an integer ranging from 1 to 3:

[0131] The preferred amidinium cations of formula (3a) corresponding to the third family of compounds (1a) are shown below. They respectively generate the active catalysts DBN (1 ,5- diazabicyclo[4.3.0]non-5-ene) and DBU (1 ,8-diazabicyclo[5.4.0]undec-7-ene), from left to right:

[0132] In another embodiment of the invention, Q in the compound of formula (3) is an alkylene group of formula (CH2)m, m being 2 or 3, preferably 3, and R1aand R4atogether form a saturated divalent radical of formula -R1a-R4a- representing a group of formula -CHR6CHR7CHR8NR5- in which R5represents a (hetero)aryl group, a substituted or unsubstituted alkyl group, R6, R7and R8independently represent a hydrogen atom, a (hetero)aryl group, a substituted or unsubstituted alkyl group, the nitrogen atom of the main chain of this group being connected to the cyclic carbon atom in the compound of formula (3). This group is preferably a group of formula - CH2CH2CH2NR5- in which R5is as defined previously and preferably represents an alkyl group.

[0133] A preferred family of such guanidinium compounds has formula (5), in which R5 to R8 are as defined above:

[0134] The preferred guanidinium cations of formula (5) are derived from 7-alkyl-1 ,5,7- triazabicyclo[4.4.0]dec-5-enes (R6= R7= R8= H and R5= alkyl having preferably from 1 to 8 carbon atoms). Another preferred iminium structure corresponding to the third family of compounds (1a) is shown hereunder. It generates the active catalyst 7-methyl-1 ,5,7- triazabicyclo[4.4.0]dec-5-ene (7-methyl TBD):

[0135] The fourth family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises compounds in which R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted 5- or 6-member heteroaromatic group.

[0136] Examples of such quaternary ammonium or quaternary iminium cations are iminium / imidazolium compounds of formula (2): wherein R1is as defined above and is preferably an aryl group having from 6 to 18 carbon atoms, R6represents a substituted or unsubstituted alkyl group or a (hetero)aryl group, R5, R7and R8independently represent a hydrogen atom, a substituted or unsubstituted alkyl group or a (hetero)aryl group, or R7and R8together form a 5- or 6-member (hetero)aromatic group with the two carbon atoms they are attached to or a saturated divalent radical of formula -R7-R8-.

[0137] The saturated divalent radical of formula -R7-R8- defined in the present application comprises carbon atoms and optionally heteroatoms such as oxygen, nitrogen and sulfur in its main chain. Said main chain preferably contains 3 to 5 atoms. The saturated divalent radical of formula -R7-R8- preferably represents a substituted or unsubstituted alkylene group, preferably a linear alkylene group of formula (CH2)P, with p being an integer ranging from 3 to 5, preferably from 3 to 4.

[0138] In one embodiment, R7and R8together form, with the two carbon atoms they are attached to, a 5- or 6-member (hetero)aromatic group, for example a 5- or 6-member heteroaromatic group or a 6-member aromatic group such as benzene group that may bear additional substituents as those disclosed above in the context of the aryl group.

[0139] R6preferably represents a substituted or unsubstituted alkyl group or a (hetero)aryl group, R5, R7and R8independently preferably represent a hydrogen atom, a substituted or unsubstituted alkyl group or a (hetero)aryl group. When R7and R8together form, with the two carbon atoms they are attached to, a 6-member aromatic group, the compound of formula (2) is a benzimidazolium cation.

[0140] A preferred imidazolium structure corresponding to the fourth family of compounds (1a) includes compounds in which R5= R7= R8= H and R6represents a substituted or unsubstituted alkyl group having preferably 1 to 8 carbon atoms, such as the structure shown hereunder. It generates the active catalyst 1 -methylimidazole:

[0141] Another example of quaternary ammonium or quaternary iminium cations corresponding to the fourth family of compounds (1a) includes pyridinium cations (R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted 6-member heteroaromatic group). Mention may be made of the compounds generating the active catalysts 2 ,6-di-tert-butylpyridine or picoline.

[0142] The fifth family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises compounds in which R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted saturated bicyclic group.

[0143] Examples of such iminium compounds are those in which R2, R3and R4together form a trivalent group of formula (7): in which A represents a nitrogen atom or a C-R14group, with R14representing a hydrogen atom, a (hetero)aryl group or a substituted or unsubstituted alkyl group, and E, D and G independently represent a divalent group. R14preferably represents a hydrogen atom. E, D and G preferably represent ethylene groups.

[0144] The fifth family of quaternary ammonium or quaternary iminium cations of formula (1a) comprises cations deriving from fused or bridged polycyclic amines, preferably bicyclic, wherein at least one of the bridgehead atoms is a nitrogen atom such as a fused or bridged bicyclic diamines having one or two nitrogen bridgehead atoms. The fifth family of quaternary ammonium or quaternary iminium cations of formula (1a) also comprises cations deriving from fused or bridged bicyclic amines having one nitrogen bridgehead atom.

[0145] Non-limiting examples of iminium compounds of the fifth family of cations of formula (1a) have formula (8), generating the active catalyst quinuclidine, or formula (9) or (9b), generating the active catalyst 1 ,4-diazabicyclo[2.2.2]octane (DABCO):

[0146] (8) (9) (9b) In one embodiment, the quaternary ammonium or quaternary iminium cation of formula (1a) is defined as having:

[0147] - R2, R3and R4independently representing a substituted or unsubstituted alkyl group having from 2 to 6 carbon atoms, or

[0148] - R2, R3and R4together forming with the quaternary nitrogen atom they are attached to a substituted or unsubstituted imidazolium group.

[0149] The preferred photo-activatable latent catalysts according to the invention are those generating the following active catalysts: 1-methylimidazolium, triethylamine, tributylamine, 1 ,5- diazabicyclo[4.3.0]non-5-ene, 1 ,8-diazabicyclo[5.4.0]undec-7-ene, 7-methyl-1 ,5,7- triazabicyclo[4.4.0]dec-5-ene, N,N-diisopropylethylamine, 2,6-di-tert-butylpyridine, N- methylmorpholine, quinuclidine and 1 ,4-diazabicyclo[2.2.2]octane. The three former compounds are the most preferred active catalysts.

[0150] In a preferred embodiment, the latent catalyst does not comprise NH or NH2 groups. Indeed, those groups with labile protons could react with NCO or NCS groups of the iso(thio)cyanate reactants to form (thio)ureas. In another embodiment, the latent catalyst does not comprise secondary amine groups or primary amine groups. In another embodiment, the latent catalyst does not comprise OH or SH groups. In another embodiment, the latent catalyst does not comprise NH, NH2, OH or SH groups, all these groups having active hydrogen atoms.

[0151] In one embodiment of the invention, the quaternary ammonium or quaternary iminium cation according to the invention is selected from the cations having the following formulae:

[0152] In another embodiment of the invention, the quaternary ammonium or quaternary iminium cation according to the invention is selected from the cations having the formulae shown on the above scheme, with the 2-naphthyl group replaced with a R1group selected from represents an (hetero)aryl groups.

[0153] The anion of the latent catalyst salt according to the invention is a borate anion of formula (1 b), in which Ra, Rb, Rcand Rdindependently represent a (hetero)aryl group or a substituted or unsubstituted alkyl group:

[0154] RaR— B-Rb(1 b) Rc

[0155] Ra, Rb, Rcand Rdare connected to the boron atom through a carbon atom and preferably represent (hetero)aryl groups, more preferably aryl groups.

[0156] In a preferred embodiment, at least two of the Ra, Rb, Rcand Rdgroups are identical or different (hetero)aryl groups.

[0157] Non-limiting examples of borate anions of formula (1 b) include n-butyltriphenylborate, n- butyltri(1-naphthyl)borate, tetrakis(3-fluorophenyl)borate, tetrakis(pentafluorophenyl) borate and tetraphenyl borate. The anion of formula (1b) is preferably a tetraaryl borate, more preferably tetraphenyl borate, for all quaternary ammonium or quaternary iminium cations mentioned in the present application.

[0158] Organoborate anions can be prepared from well-known methods starting from organomagnesium compounds, as disclosed, e.g., in US 2016 / 0108062.

[0159] Latent catalysts according to the invention can be synthesized in two steps, for example by reaction in a first step (blocking step) of an appropriate substituted or unsubstituted 2- halogeno-2-acetophenone, typically a substituted or unsubstituted 2-bromo-2-acetophenone with a nitrogen containing basic organic precursor compound (active form of the catalyst), such as DBU, DBN, 1 -methylimidazole, triethylamine, tributylamine or 7-methyl TBD, forming an ammonium or iminium salt, such as a bromide salt, and in a second step by reaction of said salt with an alkali borate precursor, for example a sodium borate compound such as a sodium tetraaryl borate compound, by an ion exchange reaction.

[0160] The required nitrogen containing basic organic precursor compounds are commercially available or can be easily synthesized from widely available and relatively cheap raw materials, such as substituted or unsubstituted 2-pyrrolidone, acrylonitrile, substituted or unsubstituted 1 ,6- hexanedial, 1 ,3-diaminopropane, through chemical reactions well known to those skilled in the art.

[0161] Without wishing to be bound by any theory, the inventors believe that the borate anion acts as a blocker and contributes to render the catalyst catalytically inactive.

[0162] The latent catalyst according to the invention is a base generator, called “photo-base generator”. Its active form is the deblocked nitrogen containing basic organic compound, which is an imine (such as an amidine, a guanidine, an imidazole) or an amine, capable of acting as a catalyst in thio-urethanization reactions. The covalent bond between the acetophenone part and the amine / imine part of the compound of formula (1 a), and the ionic bond of the salt catalyst can be broken upon photo-activation, to regenerate the basic active form of the catalyst. It is believed that the acetophenone part acts as a light receptor group, preferably a UV receptor group.

[0163] The level of light energy required to decompose the salt and liberate the active basic compound may vary depending on the nature of the borate anion and acetophenone blocking components.

[0164] Preferably, the nitrogen containing basic organic compound generated by activating the latent catalyst according to the invention has a pKa ranging from 8 to 15. In the present application, pKa is preferably expressed at 25°C. pKa can be measured in water at standard pressure by potentiometric (pH) titration, using a glass electrode and a pH meter.

[0165] Several latent catalysts according to the invention can be combined in the present process. In particular, two or more latent catalysts with different photo-activation modes can be employed.

[0166] In this case, a first latent catalyst activatable by a first radiation can form a gel while minimizing defects, and then the second latent catalyst is triggered with a different radiation to drive the polymerization to completion.

[0167] In the context of the present invention, a gel preferably designates the reaction product of components A and B in which the conversion rate of the reactive functions is significantly high. For example, said conversion rate ranges from 50 to 80% and preferably is about 70%.

[0168] An additional catalyst (co-catalyst) that is not a photo-activatable latent catalyst according to the invention can also be used in the context of the invention. Among additional non-latent catalysts that can be used in the method of the invention, there may be cited amines, such as tertiary amines (e.g., triethylamine or 3,5-lutidine), organometallic compounds, such as alkyltins or alkyltin oxides, in particular dibutyltin dilaurate, dibutyltin dichloride and dimethyltin dichloride.

[0169] Among additional latent catalysts that can be used in the method of the invention, there may be cited latent thermal catalysts such as nitrogen containing basic organic compounds blocked by isocyanates or salts of these compounds with benzoic acid or organoborborate salts of these compounds such as BPI salts.

[0170] When an additional catalyst is present, it is preferably used in a molar ratio [latent catalyst according to the invention / additional catalyst] higher than or equal to 40 / 1 , more preferably higher than or equal to 50 / 1 .

[0171] In one embodiment, the method according to the invention does not use a catalyst that is not a photo-activatable latent catalyst.

[0172] The mixing of first component A with second component B during step 3) to form a polymerizable mixture can be performed by any known mixing technique such as those mentioned in US 5973098. Preferably, components A and B to be mixed are added in a small reactor chamber and then mixed with a screw mixer. In one embodiment, the viscosity at 25°C of the mixture of components A and B ranges from 0.01 Pa.s to 5 Pa.s, preferably from 0.05 Pa.s to 0.5 Pa.s, even more preferably from 0.1 Pa.s to 0.3 Pa.s.

[0173] During step 3), a molding cavity of a casting mold assembly can be filled with the resulting polymerizable mixture of first and second components A and B.

[0174] More specifically, the optical material composition can be poured into the cavity of two mold parts held together using an annular closure such as a gasket or tape. Depending on the desired characteristics of the resulting optical material, degassing can be performed under reduced pressure and / or filtration can be performed under increased pressure or reduced pressure before pouring the optical material composition in the mold. After pouring the composition, the casting mold, preferably a lens casting mold, can be irradiated with an appropriate light source and optionally heated in an oven or a heating device immersed in water according to a predetermined temperature program to cure the resin in the mold assembly.

[0175] The curing step of the mixture, which provides a transparent substrate, is performed in the presence of the catalyst according to the invention, and can be implemented using any well known polymerization technique triggered by light irradiation. This method has the advantage of shortening the curing time.

[0176] Polymerization of the polymerizable composition is generally triggered by irradiating the composition with radiation, preferably visible or ultraviolet light, ultraviolet light being the most preferred radiation. The ultraviolet or visible light preferably includes light with a wavelength of 200 nm to 450 nm.

[0177] Preferably, UV light wavelength ranges from 320 to 390 nm. UV light intensity typically ranges from 10 to 1000 mW / cm2and the total exposure time to UV light, either in one shot or several shots, preferably ranges from 120 to 1650 seconds, more preferably from 200 to 600 seconds. In one embodiment, the polymerizable mixture is pre-heated before the photopolymerization is performed.

[0178] Devices such as a LED ultraviolet ray irradiation device, an irradiation device with laser light, a high-pressure mercury lamp, a metal halide lamp, can be employed for photo-irradiation.

[0179] In one embodiment, curing step 4) is a dual curing step, i.e., includes a thermal curing step performed after the step of photo-activating said latent catalyst (“photo-polymerization” step). Indeed, a combination of both radiation-curing and thermal curing can be employed, to complete the polymerization and increase the polymerization degree of the cured material.

[0180] Thermal polymerization includes induction and infrared heating. The curing temperature of this thermal post-cure generally ranges from 50°C to 150°C, more preferably from 80°C to 130°C. The thermal curing time is preferably lower than or equal to 2 hours, more preferably lower than or equal to 1 .5 hours or 1 hour.

[0181] The curing starts due to the photo-induced decomposition of the latent salt catalyst that releases the base. Once started, the curing is fast due to the high reactivity of amine or imine catalyst generated. The total curing time of the process (step 4) is preferably lower than 5 hours, more preferably lower than 2, 1.5 or 1.25 hours. As used herein, curing refers to a chemical process of converting a monomer or an oligomer into a polymer of higher molar mass and then into a network.

[0182] Thereafter, the mold assembly is withdrawn from the oven / curing device, the annular closure member is removed and the mold parts disassembled.

[0183] The resulting resin product may then be annealed, if necessary, at a temperature preferably ranging from 80°C to 150°C. Annealing is performed after disassembly of the mold, for a time preferably ranging from 1 to 2 hours. In one embodiment of the invention, the process according to the invention does not comprise any thermal polymerization step. In another embodiment, the latent catalyst according to the invention is not activated by heat to accelerate the polymerization reaction forming the polythiourethane-based transparent substrate.

[0184] In step 5) of the present process, the polythiourethane transparent substrate is recovered, typically from the casting mold assembly if a mold was used. The recovered substrate or article can then be edged to obtain a lens.

[0185] The present process can be used to manufacture a finished lens, having both sides at the required geometries, or a semi-finished lens, having one face that still needs to be surfaced at the required geometry.

[0186] The article resulting from the present process has satisfactory color properties, which can be quantified by the yellowness index Yi. The degree of whiteness of the inventive optical material may be quantified by means of colorimetric measurements, based on the CIE tristimulus values X, Y, Z such as described in the standard ASTM E313 with illuminant C observer 2°. The optical article according to the invention preferably has a low yellowness index Yi, i.e. , lower than 12 or 10, more preferably lower than 8, even better lower than 6, as measured according to the above standard. The yellowness index Yi is calculated per ASTM method E313 through the relation Yi = (127.69 X - 105.92 Z)) I Y, where X, Y, and Z are the CIE tristimulus values.

[0187] From the viewpoint of photo-curability, the thickness of the cured product is preferably 10 mm or less, more preferably 6 mm or less, and even more preferably 3 mm or less. The thickness of the cured product is preferably 10 nm or more, more preferably 50 nm or more, and even more preferably 100 nm or more.

[0188] Thereafter the substrate or article can be tinted or coated to improve various properties such as scratch resistance or reflection properties.

[0189] Specific examples of polythiourethane resins suitable to the present invention are those marketed by the Mitsui Chemicals company as MR® series, in particular MR6®, MR7® (refractive index: 1.67), MR8® (refractive index: 1.6) resins, MR10® (refractive index: 1.67). These optical materials as well as the monomers used for their preparation are especially described in the patents US 4,689,387, US 4,775,733, US 5,059,673, US 5,087,758 and US 5,191 ,055.

[0190] The invention also relates to a polymerizable mixture, comprising:

[0191] - a first component A comprising:

[0192] - at least one polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said pre-polymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or

[0193] - at least one polyisocyanate or polyisothiocyanate monomer A2,

[0194] - a second component B comprising:

[0195] - at least one polythiourethane pre-polymer B1 having thiol end groups, said prepolymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or

[0196] - at least one polythiol monomer B2,

[0197] - at least one photo-activatable latent catalyst composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1 b) as defined above in the present disclosure.

[0198] The polymerizable mixture according to the invention intended to form a polythiourethane resin can be distinguished from the polymerizable mixtures obtainable by the prior art processes using other catalysts by means of its extended shelf life at room temperature or higher temperatures, which is very interesting to extend the processing time before filling to the molds with said polymerizable mixture. Due to the low reactivity of the latent catalysts according to the invention in thiourethane systems in the absence of light irradiation, the polymerizable mixture can be stored for several hours before being processed.

[0199] The invention also relates to a new photo-activatable latent catalyst selected from the compounds of formulae:

[0200] The polymerizable mixture may be used as an optical material composition in additive manufacturing systems to manufacture an ophthalmic lens.

[0201] Additive manufacturing is a manufacturing technique defined in international standard ASTM 2792-12 and designates a process for assembling elements of material to obtain a solid three-dimensional object on the basis of a digital three-dimensional model (typically represented by data of a CAD file, CAD standing for “Computer-Aided Design”).

[0202] Known methods for additively manufacturing of ophthalmic lenses, such as stereolithography and its variants, comprise curing steps and layering steps which are performed successively in a manufacturing system which comprises a curing device, a layering device and a building platform located in relation to a vat filled with a predetermined material. The additive manufacturing method used may be selected in, but is not limited to, the list consisting of inkjet printing, stereolithography, mask stereolithography or mask projection stereolithography, material (such as polymer) jetting, scanning laser sintering (SLS), scanning laser melting (SLM) and fused deposition modeling (FDM).

[0203] Namely, various families of additive manufacturing technologies are known: DLP-SLA (Digital Light Processing Stereolithography) and material jetting, also known as inkjet printing, or even fused deposition modeling (FDM), etc.

[0204] According to DLP-SLA, each ophthalmic lens is built layer by layer on the building platform which is movable relative to the vat including a volume of the predetermined material. The building platform is located in a predetermined position, the curing device including an irradiation source performs the curing step of a first layer of material, the layering device performs the layering step at least thanks to a displacement of the building platform so that a novel layer of material having a predetermined thickness can be cured, etc.

[0205] In other words, in such known methods, a curing step is performed on a layer which is for instance liquid for the plurality of ophthalmic lenses to be manufactured on the building platform. The liquid layer is thus hardened and next a layering step is performed for forming a new liquid layer on the previous hardened layer of the plurality of ophthalmic lenses to be manufactured.

[0206] Another method of additive manufacturing may comprise successively depositing droplets of liquid material and curing them forming layers of material. This method, usually called 3D- printing, or inkjet printing, generally controls the shape of the layers by controlling the position and volume of the deposited droplets whereas the curing step is usually global. Other additive manufacturing method may also be used.

[0207] Other known method of additive manufacturing propose to build the whole structure or part of the whole structure without any specific layers, either as a block or as a continuously moving boundary, such as holographic printing, the so called “Xolographic”® printing technology and other similar concepts, fronto-photo-polymerization, or even some variants of continuous stereolithography.

[0208] In order to be used in such systems, the polymerizable mixture of the disclosure may need to be tuned to have a working temperature viscosity between 1 and 10000 cP, for example, from 5 to 5000 cP, and for example for stereolithography from about 10cP to 3000 cP, and, for stereolithography technologies a critical dose, or critical energy between 2 and 50 mJ / cm. The critical energy EC is determined using an empirical method based on the Jacobs’ equation (Paul F. Jacobs, Fundamentals of stereolithography in International Solid Freeform Fabrication Symposium, 1992):

[0209] { th = DP * In ( E / EC ) }, with E the curing surface energy, EC the critical energy, DP a light depth penetration value of the curing surface energy within the curable material and th the polymerized thickness.

[0210] These processes can be used to manufacture an ophthalmic lens using the polymerizable mixture of the disclosure. Such ophthalmic lens may be a finished lens, having both sides at the required geometries, or a semi-finished lens, having one face that still needs to be surfaced at the required geometry. Such lenses may have a circular or pseudo circular contour or be already at or near a contour adapted to have the lens mounted in glasses. These processes may also be used to form ophthalmic lenses based on the so-called “build over technology” by manufacturing at least one complementary optical member onto a starting optical member. Such a build over technology is disclosed for instance in international applications WO 2015 / 004383 and WO 2020 / 115061.

[0211] The following examples illustrate the present invention in a more detailed, but non-limiting manner. Unless stated otherwise, all thicknesses disclosed in the present application relate to physical thicknesses.

[0212] EXAMPLES

[0213] 1. Chemicals used

[0214] Optical materials were prepared from a composition comprising polymerizable compounds, a delayed action catalyst, and Zelec UN® (CAS 3896-11-5) as a mold release agent. The monomers used in the present examples were m-xylylene diisocyanate (CAS 3634-83-1) and 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol (CAS 131538-00-6), in order to produce a polythiourethane transparent matrix having a refractive index of 1.67.

[0215] The latent catalysts according to the invention were prepared from the following amines or imines: 1 -methylimidazole (noted 1 Ml, CAS 616-47-7), 1 ,5-diazabicyclo[4.3.0]non-5-ene (DBN, CAS 3001-72-7), 1 ,8-diazabicyclo[5.4.0]undec-7-ene (DBU, CAS 6674-22-2), tributylamine, triethylamine, 1 ,4-diazabicyclo[2.2.2]octane (DABCO) or N-methylmorpholine, as described in § 3.

[0216] Two non-latent thermal catalysts were used for comparative purposes: dimethylin dichloride and the catalyst system disclosed in US 2003 / 125410 (8.5 % KSCN, 34.84 % 18-crown- 6, 56.66 % 2-mercaptoethanol, by weight).

[0217] 2. Evaluation of the polymerizable composition and of lenses after curing

[0218] The following test procedures were used to evaluate the optical articles prepared according to the present invention. Several samples for each system were prepared for measurements and the reported data were calculated with the average of the different samples.

[0219] The glass transition temperature (Tg) and tensile storage modulus (E’) of the lenses have been evaluated by DMA (dynamic mechanical analysis) using a dynamic mechanical analyzer Q800 module supplied by TA Instruments. Measurements were conducted in the multi-frequency strain mode on the final material. A sample was in rectangular shape with dimensions of 50x8x2 mm. The operating was performed at a heating rate of 2°C / min from 25-130°C at a 30 pm amplitude, pre-load force 0.5 N with force track 150 %. The storage modulus makes it possible to evaluate the ability of the material to store an input mechanical energy elastically.

[0220] DSC (Differential scanning calorimetry) was used to determine the melting point of the latent catalysts. The device used was a differential scanning calorimeter DSC 823e supplied by Mettler Toledo. The experiments were carried out under nitrogen with a flow rate of 60 mL / min. Sample weights were 5-12 mg to ensure sufficient sensitivity for heat capacity measurements.

[0221] The yellowness index Yi of the prepared optical materials was calculated as described above, by measuring on a white background with a Cary 60 spectrophotometer the CIE tristimulus values X, Y, Z such as described in the standard ASTM E 313-05, through reflection measures, with biplano lenses having a thickness of 6 mm.

[0222] The infrared transmission spectra at normal incidence were measured with a Nicolet iS50 FTIR spectrometer in a range of 500-4500 cm-1with a resolution of 8 cm-1to calculate the progression of the condensation reaction.

[0223] Transmission corresponding to the NCO functional group resonance frequency was taken at 2260 cm-1and the peak at 2925 cm-1assigned to the CH2 group of the thiol monomer was used as a normalized signal. The NCO groups conversion was calculated based on a spectrum of the final polythiourethane substrate obtained from FTIR using the equation below:

[0224] NCO conversion (%) = (x — y) / x ■ 100 where x is the average transmission ratio of NCO / CH2 groups in the starting composition before reaction and y is the average transmission ratio of NCO / CH2 groups in the solid resin obtained (before annealing). The higher the NCO conversion, the more complete the polymerization reaction.

[0225] Defects were inspected in depth in the final material using an arc lamp. A rating “A” means no striation, no bubbles. A rating “B” means a few striations and / or bubbles. A rating “C” means a lot of striations and / or bubbles.

[0226] 3. Synthesis of the ammonium and iminium borate latent catalysts

[0227] The synthesis of the latent catalysts according to the invention was divided into two main steps: (1) the synthesis of an ammonium or iminium bromide salt and (2) the synthesis of the tetraphenylborate salt.

[0228] In the first step, 2-bromo-2-acetonaphthone and an excess of the required amine or imine were separately dissolved in acetone. Then, the amine or imine was dropped into the 2-bromo-2- acetonaphthone solution, and the mixture was stirred for 1 hour at room temperature. The solvent was removed in a rotary evaporator to provide the crude ammonium or iminium bromide salt. Alternatively, if the ammonium or iminium bromide salt precipitated, it was filtered off and rinsed with cold acetone. In the second step of the synthesis, the ammonium or iminium bromide salt was resolubilized in ethanol, while an excess of sodium tetraphenylborate (NaBPh4) was also separately dissolved in the same solvent. The ammonium or iminium bromide salt was then added to the NaBPh4 solution, and the reaction was allowed to proceed for an h our at room temperature under stirring, forming a colorless precipitate, which was filtered, rinsed with ethanol and dried at 50°C.

[0229] The structures of the latent catalysts according to the invention that have been prepared are shown hereunder:

[0230] These blocked catalysts can be deblocked by irradiation, releasing the basic (amine or imine) active form of the catalyst (DBU, DBN, 1 -methylimidazole, 4-methylmorpholine, quinuclidine, triethylamine, tributylamine or DABCO).

[0231] The chemical structure of the latent catalysts was confirmed by FTIR and NMR techniques.

[0232] The characteristic peaks of PBG-TEA appeared as follows on the FTIR spectrum: 684- 845 cm-1(C-H out of plan, aromatic ring), 1067-1278 cm-1(C-N stretching), 1394-1427 cm-1(CH3bending), 1477 cm-1(CH2bending), 1690 cm-1(C=O stretching), and 2984-3053 cm-1(C-H stretching). The melting point of PBG-TEA measured by DSC was 165°C. UV-Vis absorption at 365 nm was 0.0131 (0.05 mM, ethyl acetate as solvent).

[0233] The characteristic peaks of PBG-TBA appeared as follows on the FTIR spectrum: 684- 895 cm-1(C-H out of plan, aromatic ring), 1068-1275 cm-1(C-N stretching), 1355-1408 cm-1(CH3bending), 1456 - 1472 cm-1(CH2bending), 1695 cm-1(C=O stretching), and 2873-3054 cm-1(C- H stretching). The melting point of PBG-TBA measured by DSC was 160°C. UV-Vis absorption at 365 nm was 0.0166 (0.05 mM, ethyl acetate as solvent).

[0234] The characteristic peaks of PBG-1 MI appeared as follows on the FTIR spectrum: 704-888 cm-1(C-H out of plan, aromatic ring), 1032-1276 cm-1(C-N stretching), 1627 cm-1(C=N stretch), 1704 cm-1(C=O stretching), and 2925-3162 cm-1(C-H stretching). The melting point of PBG-1 MI measured by DSC was 161 °C. UV-Vis absorption at 365 nm was 0.0036 (0.05 mM, ethyl acetate as solvent).

[0235] The characteristic peaks of the 4-methylmorpholinium compound represented above appeared as follows on the FTIR spectrum: 684-895 cm-1(C-H out of plan, aromatic ring), 1192- 1292 cm-1(C-N stretching), 1372-1477 cm-1(CH2 and CH3 bending), 1058 cm-1(C-0 stretching), 1700 cm-1(C=O stretching), and 2871-3052 cm-1(C-H stretching). The melting point of this compound measured by DSC was 231 °C (measured by DSC). UV-Vis absorption at 365 nm was 0.02086 (0.05 mM, acetone as solvent).

[0236] 4. Preparation of polythiourethane pre-polymer A1 having isocyanate end groups

[0237] In a reactor eguipped with a condenser, a thermal probe and an agitator, a determined amount of the polyisocyanate monomer m-xylylene diisocyanate (33.62 % wt.) was charged and heated up to 118°C. Then, 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol was introduced and mixed with the polyisocyanate in an amount (10.34 % wt.) such that the molar ratio of the isocyanate functions to the thiol functions NCO / SH was 3: 1. The mixture was heated for 3.5 hours and then cooled to room temperature and an additional amount of the polyisocyanate monomer m-xylylene diisocyanate (56.04 % wt.) was added to the mixture. The resulting mixture was transferred into an appropriate container, tapped with inert gas (nitrogen or argon) and stored in a cold room. The final molar ratio of NCO / SH was 8:1 . Pre-polymer A1 with isocyanate end groups was prepared without the use of catalyst.

[0238] 5. Preparation of polythiourethane pre-polymer B1 having thiol end groups

[0239] In a reactor eguipped with a condenser, a thermal probe and an agitator, a determined amount of the polythiol monomer 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol (66.05 % wt.) was charged and heated up to 93°C. Then, m-xylylene diisocyanate was introduced and mixed with the polythiol in an amount (11 .93 % wt.) such that the molar ratio of the thiol functions to the isocyanate functions SH / NCO was 6:1. The mixture was heated for 3.5 hours and then cooled to room temperature and an additional amount of the polythiol monomer 2,3-bis((2- mercaptoethyl)thio)-1 -propanethiol (22.02 % wt.) was added to the mixture. The resulting mixture was transferred into an appropriate container, tapped with inert gas (nitrogen or argon) and stored in a cold room. The final molar ratio of SH / NCO was 8:1. Pre-polymer B1 with thiol end groups was prepared without the use of catalyst.

[0240] 6. Preparation of polythiourethane transparent casted substrates Convex and concave molds were assembled by using a tape. Center thickness was 2 mm. In examples 1-10, 45.5 to 52 g of the polyisocyanate compound (pre-polymer A1 mixture prepared above or monomer A2) were mixed with 0.1 g of Zelec UN® and a latent catalyst in a content specified in table 1. This mixture was stirred at room temperature and degassed for 45 minutes to form component A. 42 to 54.5 g of the polythiol compound (pre-polymer B1 mixture prepared above or monomer B2) were separately stirred at room temperature and degassed for 45 minutes to form component B. Components A and B were then mixed in a small reactor while stirring and degassing for 30 minutes at room temperature. Once the mixing was complete, molds were filled with the help of a clean syringe. The assembled molds were held at room temperature for 10 minutes before inserting them in a UV oven equipped with 365 nm LED at both top and bottom sides, and the irradiation was done for 5 minutes, followed by thermal curing in a convection oven at 120°C for 60 minutes, to carry out the polymerization reaction. After the polymerization process, the assembled molds were removed from the oven and allowed to cool at room temperature for 5-10 minutes. The molds were then disassembled to obtain piano (no power) lenses with 2 mm center thickness comprising a body of polythiourethane transparent thermoset substrate having a refractive index of 1.67. The lenses were cleaned by immersion and sonication in a surfactant solution, then rinsed, put on a rack and annealed at 120°C for 1h in a thermal oven.

[0241] In comparative examples 1-3, the (non-latent) thermal catalyst dimethyltin dichloride was used under identical process conditions, except that mixing of the catalyst and mixing of components A and B before filling of the mold were done at a temperature lower than 10°C to prevent premature gelation. After filling the mold, the assemblies were let gelled for 5 minutes and thermally cured in a convection oven at 120°C for 60 minutes.

[0242] In comparative example 4, another non-latent thermal catalyst (KSCN, 18-crown-6, 2- mercaptoethanol) was used under identical process conditions, except that the catalyst was mixed with the polythiol compound rather than the polyisocyanate compound, and mixing of the catalyst and mixing of components A and B before filling of the mold were done at a temperature lower than 10°C to prevent premature gelation. After filling the mold, the assemblies were let gelled for 10 minutes and thermally cured in a convection oven at 120°C for 3 hours.

[0243] In all examples and comparative examples, the molar ratio of NCO to SH groups was 1.

[0244] The polymerization conditions (nature and amounts of reactants and catalysts) are shown in table 1 . Examples 1-3 involved only monomers, examples 4-6 involved only pre-polymers, while examples 7-10 combined a monomer and a pre-polymer.

[0245] In terms of catalyst weight amount, 0.3 % by weight of latent catalyst PBG-TEA (M = 589.64 g / mol) corresponds to 0.05 % by weight of the active catalyst, which is triethylamine (M = 101.19 g / mol, representing 17.16 % of the catalyst total weight). This amount is comparable to that of comparative example C2 (0.05 % of dimethyltin dichloride).

[0246] In terms of catalyst weight amount, 0.3 % by weight of latent catalyst PBG-1 MI (M = 570.55 g / mol) corresponds to 0.043 % by weight of the active catalyst, which is 1 -methylimidazole (M = 82.1 g / mol, representing 14.39 % of the catalyst total weight).

[0247] In terms of catalyst weight amount, 0.3 % by weight of latent catalyst PBG-TBA (M = 673.8 g / mol) corresponds to 0.08 % by weight of the active catalyst, which is tributylamine (M = 185.36 g / mol, representing 27.5 % of the catalyst total weight). This amount is comparable to that of comparative example 03 (0.08 % of dimethyltin dichloride).

[0248] The thermo-mechanical and cosmetic properties of the optical articles prepared using the different catalysts are shown in table 2.

[0249] Table 1 In each experiment, the molar ratio of NCO to SH groups was 1 . Table 2

[0250] The latent catalysts according to the invention regenerate the active form of the catalyst (triethylamine, tributylamine, 1 -methylimidazole...) upon activation. They allow a more significant control of the polymerization reaction at room temperature, since they are in a blocked state, so that the reactivity of the system is limited and there is no need to cool down the reaction mixture to 10°C to prevent premature gelation, which was required in comparative examples C1 to C4.

[0251] As a comparison, the catalyst system of comparative example C4 (8.5 % KSCN, 34.84 % 18-crown-6, 56.66 % 2-mercaptoethanol, by weight) used at a concentration of 0.4 % by weight with respect to the total weight of polymerizable compounds present in the mixture of components A and B caused the mixture to gel in 20 minutes at room temperature.

[0252] The mechanical properties (storage modulus) of all samples were comparable, with differences within the tolerance of standard deviation (+ / - 0.2 GPa). In most cases, 5 minutes of UV irradiation followed by 60 minutes of thermal curing allowed to reach conversions higher than or equal to 98 % (before annealing). In example 1 , 5 minutes of UV irradiation followed by 15 minutes of thermal curing provided a conversion rate of 91 .2 %.

[0253] The annealing treatment allowed to increase the % conversion by 0.5 to 2.3 % in all examples and comparative examples and to drive the conversion to completion or almost to completion, with percentages of conversion ranging from 97.6 % to 100 %.

[0254] The use of two pre-polymers in the polymerizable composition (examples 4-6) allowed to obtain the most complete polymerization reactions forming the polythiourethane polymer with the same latent catalyst used. This may be due to the fact that partial polymerization was done during pre-polymerization, leaving less burden for the rest of the reaction to be completed.

[0255] The embodiment in which a polyisocyanate or polyisothiocyanate monomer A2 was reacted with a pre-polymer B1 having thiol end groups was the least favorable in terms of conversion rate (examples 7, 8). Without wishing to be bound by any theory, the inventors believe that the difference of viscosity between the two reactants was the most important. Example 7 obtained the lowest glass transition temperature due to the least complete polymerization reaction and would require more than 5 minutes UV irradiation to complete the reaction.

[0256] The lenses having 2 mm thickness did not show any striations nor bubbles in examples 1-6 and 8. Some embodiments combining a monomer and a pre-polymer led to inferior results in terms of cosmetic appearance (examples 7, 9, 10).

[0257] The use of at least one pre-polymer in the polymerizable composition (examples 4-10) provided final materials with a lower yellowness index than polymerizable compositions containing only monomers (examples 1-3) with the same latent catalyst (compare examples 1 , 4, 7, 8; examples 2, 5, 8, 10). This might be due to a difference in the reactivity of the starting materials, monomers being more reactive than pre-polymers, and occurrence of undesirable side-reactions involving catalyst fragments.

[0258] The embodiment of the present invention involving the use of at least one polythiourethane pre-polymer B1 having thiol end groups and at least one polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups (steps 1 and 2) provided the best results in terms of thermo-mechanical properties, conversion rate, yellowness index and cosmetic defects (examples 4-6).

Claims

CLAIMS1. A process of curing a polythiourethane-based transparent substrate, comprising the following steps 1), 2), 3), 4) and 5), 1), 2’), 3), 4) and 5), T), 2), 3), 4) and 5) or T), 2’), 3), 4) and 5):1) Providing a first component A comprising at least one polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said prepolymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, orT) Providing a first component A comprising at least one polyisocyanate or polyisothiocyanate monomer A2,2) Providing a second component B comprising at least one polythiourethane pre-polymer B1 having thiol end groups, said pre-polymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or2’) Providing a second component B comprising at least one polythiol monomer B2,3) Mixing together first and second components A and B to form a polymerizable mixture,4) Curing said polymerizable mixture to obtain a polythiourethane-based transparent substrate, and5) Recovering the polythiourethane-based transparent substrate, wherein at least one photo-activatable latent catalyst composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1b) is added in the process prior to curing step 4):in which Ra, Rb, Rcand Rdindependently represent a (hetero)aryl group or a substituted or unsubstituted alkyl group, R1represents an (hetero)aryl group, and:- R2, R3and R4independently represent a substituted or unsubstituted alkyl group or a (hetero)aryl group, or- R3represents a substituted or unsubstituted alkyl group or a (hetero)aryl group and R2and R4together form a divalent radical of formula -R2-R4-, or- R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted unsaturated 5- or 6-member non-aromatic heterocyclic group, or- R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted 5- or 6-member heteroaromatic group, or- R2, R3and R4together form with the quaternary nitrogen atom they are attached to a substituted or unsubstituted saturated bicyclic group, and said latent catalyst is subsequently photo-activated to carry out a polymerization reaction forming the polythiourethane-based transparent substrate.

2. The process of claim 1 , wherein said latent catalyst is added to the polythiol and polyisocyanate or polyisothiocyanate monomers during the preparation of said polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups or to the polythiol and polyisocyanate or polyisothiocyanate monomers during the preparation of said polythiourethane pre-polymer B1 having thiol end groups.

3. The process of claim 1 , wherein said latent catalyst is added to the first component A obtained in step 1) or T) prior to mixture with component B or to the second component B obtained in step 2) or 2’) prior to mixture with component A.

4. The process of claim 1 , wherein said latent catalyst is added to the mixture of components A and B in step 3).

5. The process according to any one of the preceding claims, wherein said latent catalyst is photo-activated during curing step 4).

6. The process according to any one of the preceding claims, wherein curing step 4) includes a thermal curing step performed after the step of photo-activating said latent catalyst.

7. The process according to any one of the preceding claims, wherein R1is a substituted or unsubstituted naphthyl group.

8. The process according to any one of the preceding claims, wherein said quaternary ammonium or quaternary iminium cation of formula (1a) is defined as having:- R2, R3and R4independently representing a substituted or unsubstituted alkyl group having from 2 to 6 carbon atoms, or- R2, R3and R4together forming with the quaternary nitrogen atom they are attached to a substituted or unsubstituted imidazolium group.

9. The process according to any one of the preceding claims, wherein said quaternary ammonium or quaternary iminium cation is an iminium compound of formula (2):wherein R1is an aryl group having from 6 to 18 carbon atoms, R6represents a substituted or unsubstituted alkyl group or a (hetero)aryl group, R5, R7and R8independently represent a hydrogen atom, a substituted or unsubstituted alkyl group or a (hetero)aryl group, or R7and R8together form a 5- or 6-member (hetero)aromatic group with the two carbon atoms they are attached to or a saturated divalent radical of formula -R7-R8-.

10. The process according to any one of claims 1 to 8, wherein said quaternary ammonium or quaternary iminium cation is selected from the cations of formulae:

11. The process according to any one of the preceding claims, wherein the anion of the catalyst of formula (1b) is tetraphenyl borate.

12. The process according to any one of the preceding claims, wherein the total curing time of the process is lower than 2 hours, preferably lower than 1.25 hour.

13. The process according to any one of the preceding claims, wherein the substrate is an optical lens substrate.

14. A polymerizable mixture, comprising:- a first component A comprising:- at least one polythiourethane pre-polymer A1 having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said pre-polymer A1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or- at least one polyisocyanate or polyisothiocyanate monomer A2,- a second component B comprising:- at least one polythiourethane pre-polymer B1 having thiol end groups, said prepolymer B1 having been prepared from at least one polythiol monomer and at least one polyisocyanate or polyisothiocyanate monomer, or- at least one polythiol monomer B2,- at least one photo-activatable latent catalyst composed of a quaternary ammonium or quaternary iminium cation of formula (1a) and a borate anion of formula (1b) as defined in any one of claims 1 to 11.

15. A photo-activatable latent catalyst selected from the compounds of formulae:

Images