Optical material derived from a prepolymer obtained from a heterodifunctional alkyne compound

Abstract

The invention relates to a polymerizable composition comprising a) at least one polyiso(thio)cyanate and at least one prepolymer having thiol end groups obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I), or b) at least one polythiol and at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, obtained from the reaction of a mixture of at least one polyiso(thio)cyanate and at least one polymerizable compound of formula (I), in which R1 and R2 represent a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1 and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, Z represents OH, SH, NH2 or NHR4 in which R4 represents a substituted or unsubstituted alkyl group or (hetero)aryl group, and R3 represents a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or a CR'1R'2Z' group in which R'1, R'2 and Z' are defined as R1, R2 and Z. (Formula (I))

Description

[0001] Optical material derived from a prepolymer obtained from a heterodifunctional alkyne compound

[0002] The present invention relates to optical materials having improved thermomechanical properties, in particular impact resistance, which can be used in particular in optical substrates such as ophthalmic lenses, having generally a middle or high refractive index. The present invention is also directed to a polymerizable composition, a prepolymer, and a method of making the optical material.

[0003] BACKGROUND AND SUMMARY OF THE INVENTION

[0004] Plastic materials have been developed as alternatives and replacements for glass in applications such as optical lenses, fiber optics, windows, and automotive, nautical and aviation industries. As compared to inorganic glass, organic polymeric materials are advantageous in terms of light weight, impact resistance, ease of molding and dyeability.

[0005] Optical elements prepared from a variety of durable organic polymers have been developed, including polythiourethane obtained by condensation of polyiso(thio)cyanate and polythiol monomers, which are disclosed for example in the applications WO 00 / 26272, US 2007 / 098999, WO 2021 / 182526, EP 3916470 and EP 3919967.

[0006] Polythiourethane materials display relatively high refractive indexes and are of major interest since this property allows the manufacture optical articles such as lenses of lower thickness for an equivalent corrective power. However, most resulting polythiourethane polymers display poor mechanical performances, such as low glass transition temperature and low impact resistance.

[0007] US 2016 / 376453 discloses a curable composition comprising a polythiol constituent, an alkene-containing and / or alkyne-containing constituent, and an epoxy-containing constituent. The polythiol constituent can derive from a mercaptan-containing terpene or terpenoid, a mercaptan- containing cyclic alkene, a mercaptan-containing polycyclic alkene, a linear alkene, a mercaptan- containing alkyne, a mercaptan-containing unsaturated fatty acid, a mercaptan-containing unsaturated fatty ester, or a mercaptan-containing polyalkene. The cured composition is used for making cell phone cases or expanded polystyrene foam. However, three different chemicals need to be synthesized then blended to obtain the polymerizable composition.

[0008] US 2008 / 0125570 discloses an optical article comprising a reaction product of (A) a reactive compound comprising a material having functional groups that are reactive with active hydrogens such as isocyanate groups; (B) a thioether-functional, oligomeric polythiol prepared by reacting together a compound having at least two thiol functional groups, a hydroxyl functional compound having triple bond functionality; and a compound having at least two double bonds. The hydroxyl functional compound having triple bond functionality is used in high amounts to produce the polymer material (in stoichiometric amount relative to the other monomers) and therefore constitutes a backbone of the network. EP 3257876 describes a polymerizable composition comprising 100 parts by weight of a terminal dialkyne compound and 25-75 parts by weight of a polythiol, which is used to obtain materials having a high refractive index. As the dialkyne is used in high quantity, the glass transition temperature of the material is expected to be very low.

[0009] EP 2980113 discloses a polymerizable composition for an optical material comprising a polythiol compound and a difunctional compound having a carbon-carbon triple bond and at least one group selected from an isocyanate group and an isothiocyanate group, such as propargyl isocyanate.

[0010] JP 2019 / 026755 and JP 2019 / 142849 describe an optical material composition that contains a compound having two or more alkyne groups in terminal position, which is polymerizable with a polythiol compound.

[0011] Thus, there is a need in the art to develop a polymeric material having adequate refractive index and glass transition temperature, good impact resistance / strength for practical use in optical articles, at a reasonable cost.

[0012] The present invention relates to a polymerizable composition comprising: a) at least one polyisocyanate or polyisothiocyanate and a component B comprising at least one prepolymer having thiol end groups, said component B being obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I), or b) at least one polythiol and a component A comprising at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said component A being obtained from the reaction of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I), in which R1and R2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, Z represents OH, SH, NH2 or NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, and R3represents a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or a group or formula:

[0013] R'1

[0014] Z' —

[0015] R'2in which R’1and R’2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group, Z’ represents OH, SH, NH2 or NHR’4in which R’4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of SH / alkyne groups present in all said polymerizable compounds is higher than or equal to 7, and the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / alkyne groups present in all said polymerizable compounds is higher than or equal to 6, X being O or S.

[0016] The present inventors have found that alkyne compounds of formula (I) having at least one active hydrogen bearing group could be used as modifiers in a standard polythiourethane composition containing polythiols and polyiso(thio)cyanates. This addition of alkyne co-monomers allows to make a standard polythiourethane resin, having poor impact resistance, compatible with FDA impact resistance requirements, without the need to use a specific coating or plastifiers providing this property, while at the same time improving the glass transition temperature and / or elastic modulus of the material in some embodiments.

[0017] The present invention provides polythiourethane polymer networks modified by increased crosslinking from thiol-yne reactions providing thioether functionality, thanks to specifically designed starting materials co-polymerizable with polythiols and poly(iso)thiocyanates, and partially curable through photochemical processes. Improving impact resistance of a material by increasing crosslinking with an alkyne modifier is an innovative approach.

[0018] Also it has been found that the introduction of alkyne co-monomers decreases the reaction time to reach a defined level of conversion rate of polyisocyanate or polyisothiocyanate compounds in the optical material according to the invention.

[0019] The foregoing and other objects, features and advantages of the present invention will become readily apparent to those skilled in the art from a reading of the detailed description hereafter when considered in conjunction with the accompanying drawings, wherein figure 1 represents a FTIR spectrum of the initial monomer formulation, before reaction and figure 2 represents a FTIR spectrum of the obtained polymer after a certain reaction time.

[0020] DETAILED DESCRIPTION OF THE INVENTION

[0021] The terms “comprise” (and any grammatical variation thereof, such as “comprises” and “comprising”), “have” (and any grammatical variation thereof, such as “has” and “having”), “contain” (and any grammatical variation thereof, such as “contains” and “containing”), and “include” (and any grammatical variation thereof, such as “includes” and “including”) are open- ended linking verbs. They are used to specify the presence of stated features, integers, steps or components or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps or components or groups thereof. As a result, a method, or a step in a method, that “comprises,” “has,” “contains,” or “includes” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more steps or elements.

[0022] Unless otherwise indicated, all numbers or expressions referring to quantities of ingredients, ranges, reaction conditions, etc. used herein are to be understood as modified in all instances by the term "about."

[0023] In the present description, unless otherwise specified, an optical article / material is understood to be transparent when the observation of an image through said optical article is perceived with no significant loss of contrast, that is, when the formation of an image through said optical article 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.

[0024] The optical material of the invention is an organic glass, made from a thermosetting resin. The polymer matrix of said material is obtained by polymerization of a polymerizable composition comprising: a) at least one polyisocyanate or polyisothiocyanate and a component B comprising at least one prepolymer having thiol end groups, said component B being obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I), or b) at least one polythiol and a component A comprising at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said component A being obtained from the reaction of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I), in which R1and R2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, Z represents OH, SH, NH2 or NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, and R3represents a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or a group or formula:

[0025] R'1

[0026] Z' —

[0027] R'2 in which R’1and R’2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group, Z’ represents OH, SH, NH2 or NHR’4in which R’4represents a substituted or unsubstituted alkyl group or (hetero)aryl group.

[0028] The optical material of the invention can be used as the substrate of an optical article, preferably an optical lens or lens blank, more preferably an ophthalmic lens or lens blank, such as a plastic eyeglass lens. It can also be used as a coating.

[0029] 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, piano, solar and Fresnel lenses or any other kind of lenses having a discontinuous surface.

[0030] Although ophthalmic optics is a preferred field of the invention, it will be understood that this invention can be applied to optical articles of other types, such as, for example, lenses for optical instruments, in photography or astronomy, optical sighting lenses, ocular visors, optics of lighting systems, screens, glazing, windshields, sport masks, face shields, goggles, optical coatings or adhesives, etc.

[0031] 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 from 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.

[0032] 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 made of the present optical material having the shape of an optical article, for example 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 article and more particularly of the optical lens. This material may act as support for a stack of one or more coatings or layers.

[0033] From the viewpoint of reducing the thickness of a lens, a plastic material having a high refractive index is desired. The refractive index of the optical material according to the invention is preferably higher than or equal to 1 .50, more preferably 1 .52 or greater or 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, 1.67 or greater, 1.70 of greater, or 1.72 or greater, and it is preferably 1.80 or less, more preferably 1.75 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.

[0034] The refractive index of the optical material can be tuned by adapting the structure of the polymerizable precursors, in particular the weight amount represented by sulfur atoms in the monomers, typically the polythiol monomer or the difunctional compound of formula (I). The refractive index of the material can also be increased by the presence of one or more aromatic groups in the structure of at least one polymerizable precursor.

[0035] In one embodiment, the optical material according to the invention is thin, i.e. , it preferably has a center thickness of 2 mm or less, more preferably 1.5 mm or less and even better 1 .2 or 1.1 mm or less.

[0036] The optical material according to the invention preferably has a glass transition temperature higher than or equal to 70, 75, 80, 85, 90, 95 or 100°C. It is preferably lower than or equal to 200°C. The glass transition temperature can be measured by DMA (dynamic mechanical analysis).

[0037] The modulus of elasticity E (or Young's modulus, or storage modulus, or tensile modulus of elasticity) of the optical material according to the invention is preferably higher than or equal to 2.5, 3, 3,2, 3,4 or 3.6 GPa. The modulus of elasticity E of a material evaluates the ability of the material to deform under the effect of a force applied. It can be measured by DMA (dynamic mechanical analysis).

[0038] The optical material according to the invention preferably has a relative light transmission factor in the visible spectrum Tv higher than or equal to 70 %, preferably higher than or equal to 75 %, more preferably higher than or equal to 80 %, and better higher than or equal to 85 %.

[0039] The Tv factor, also called “luminous transmission" of the system, is such as defined in ISO standard 13666:1998 and is measured according to the standard ISO 8980-3. It is defined as the average transmission in the 380-780 nm wavelength range that is weighted according to the sensitivity of the eye at each wavelength of the range and measured under D65 illumination conditions (daylight). Transmissions are expressed for 2 mm thick optical articles, measured at the center of the optical article and at a normal incidence of the light beam (0° from the normal).

[0040] The optical material according to the invention 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 8, more preferably lower than 6, even better lower than 4, 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.

[0041] The polymerizable composition leading to the optical material is obtained from three main components, namely a polythiol, a polyiso(thio)cyanate and a heterodifunctional alkyne compound of formula (I), having at least one alkynylene -C=C- group and at least one Z group bearing a heteroatom (O, S or N) with at least one active hydrogen atom.

[0042] In one embodiment, said compound of formula (I) and said polythiol are different compounds.

[0043] The compound of formula (I) is generally referred two as a difunctional compound by convention, but may in fact comprise more than two reactive functions, e.g., when at least one of its substituents R1, R2or R3comprises at least one reactive function. In one embodiment, the polymerizable compound of formula (I) comprises less than two thiol functions, preferably 0 or 1 thiol function. In one embodiment, the polymerizable compound of formula (I) comprises less than two iso(thio)cyanate functions, preferably no iso(thio)cyanate function.

[0044] The polymerizable composition can be obtained from only one type of compound of formula (I), or a mixture of compounds of formula (I) having different structures. As used herein, the “polymerizable composition" without further details refers to that containing the prepolymer according to the invention and the complementary polymerizable compound.

[0045] The prepolymers are obtained from non-stoichiometric blends of at least two monomers that are reacted to obtain oligomers, specifically from a minor amount of a given monomer in an excess amount of the other monomer.

[0046] The polymerizable composition according to the invention is obtained in two steps, including a step of preparing a prepolymer having iso(thio)cyanate or thiol end groups, and a step of adding to said prepolymer a complementary polymerizable compound. Depending on the nature of the end groups of the prepolymer, the complementary polymerizable compound is a polythiol or a polyiso(thio)cyanate.

[0047] Thus, the prepolymer according to the invention is a polymerizable compound (adduct) that is intended to further react with a complementary polymerizable compound (generally a monomer) so as to provide the final optical material.

[0048] In the first main embodiment of the present invention, a prepolymer having thiol end groups is prepared from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I), the former being used in excess. The component B comprises therefore oligomers resulting from thiol-yne condensations and the initial monomers that did not polymerize, if any, which are mainly polythiols.

[0049] In the second main embodiment of the present invention, a prepolymer having isocyanate or isothiocyanate end groups is prepared from the reaction of a mixture of at least one polyiso(thio)cyanate and at least one polymerizable compound of formula (I), the former being used in excess. The component A comprises therefore oligomers (resulting from condensations of iso(thio)cyanates and active hydrogen bearing groups) and the initial monomers that did not polymerize, if any, which are mainly polyiso(thio)cyanates.

[0050] The polymerizable composition can comprise additional polymerizable compounds that are neither compounds of formula (I) according to the invention nor polythiols nor polyiso(thio)cyanates. In one embodiment, such additional polymerizable compounds (comonomers) are copolymerizable with at least one of compounds of formula (I) according to the invention, polyiso(thio)cyanates and polythiols. The additional polymerizable compounds mentioned above can also be used in the polymerizable composition forming the prepolymer according to the invention (having -SH or -NCX end groups), i.e. , during the reaction of at least one polythiol and at least one polymerizable compound of formula (I) (first main embodiment of the present invention) or during the reaction of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I) (second main embodiment of the present invention).

[0051] The polythiols, polyiso(thio)cyanates and compounds of formula (I) according to the invention preferably represent at least 50 % by weight relative to the total weight of polymerizable compounds used to prepare the polymerizable composition, i.e., polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition, more preferably at least 60 %, 70 %, 80 %, 90 %, 95 %, 99 %, or 100 % by weight.

[0052] In one embodiment, the polymerizable composition comprises less than 5 % by weight of polymerizable compounds having at least two C=C double bonds, more preferably less than 4, 3, 2 or 1 % by weight, relative to the total weight of polymerizable compounds present in said composition, even more preferably does not comprise any polymerizable compound having at least two C=C double bonds. In one embodiment, the prepolymer according to the invention is not formed from a polymerizable compound having at least two C=C double bonds. In another embodiment, less than 5 % by weight of polymerizable compounds having at least two C=C double bonds, more preferably less than 4, 3, 2 or 1 % by weight, are used to prepare the prepolymer according to the invention, relative to the total weight of polymerizable compounds used to prepare said prepolymer.

[0053] Examples of polymerizable compounds that are neither compounds of formula (I) according to the invention nor polythiols nor polyiso(thio)cyanates include polyols, polyamines, epoxy-containing compounds.

[0054] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polythiols represent from 35 % to 70 % by weight relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition), more preferably from 38 % to 65 % by weight, 40 to 60 % by weight, 42-58 % by weight, 44-54 % by weight or 52-54 % by weight. In another embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polythiols represent from 38 to 58 % by weight relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition).

[0055] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that trithiols represent from 35 % to 42 % by weight and tetrathiols represent from 3 % to 16 % by weight, relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition). In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polyiso(thio)cyanates represent from 20 % to 70 % by weight relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition), more preferably from 25 % to 65 % by weight, 30 to 60 % by weight, 40-50 % by weight, 47-55 % by weight, or 42-47.5 % by weight. The compound of formula (I) is used as a modifier in the preparation of the polymerizable composition obtained from polythiols and polyiso(thio)cyanates as major components, which means that the backbone of the optical material according to the invention is polythiourethane.

[0056] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the compounds of formula (I) represent from 0.15 % to 4 or 5 % by weight relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition), more preferably from 0.2 % to 3.5 % by weight, 0.25 % to 3 % by weight, 0.25 % to 2.5 % by weight, 1 % to 3 % by weight or 0.3 to 2 % by weight. When the amount of alkyne compounds of formula (I) increases, the polymer network becomes richer in thioether bonds resulting from the reaction of alkyne and thiol functions, which creates S-C bonds.

[0057] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polyiso(thio)cyanates and polythiols represent from 80 % to 99.85 % by weight relative to the total weight of (polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition), more preferably from 85 % to 99.85 % by weight, 90 % to 99.85 %, 95 % or 96 % to 99.85 %, 96.5 % to 99.8 % by weight, 97 % to 99.75 % by weight, 97.5 % to 99.75 % by weight, or 98 % to 99.7 % by weight.

[0058] In one embodiment, the polymerizable composition comprises from 35 % to 65 % by weight of prepolymer according to the invention relative to the total weight of polymerizable compounds present in said polymerizable composition, more preferably from 40 % to 60 % by weight, even more preferably from 40 % to 50 %.

[0059] In one embodiment, the polymerizable composition comprises from 35 % to 65 % by weight of complementary polymerizable compound according to the invention (which is either the polythiol or poly(iso)thiocyanate) relative to the total weight of polymerizable compounds present in said polymerizable composition, more preferably from 40 % to 60 % by weight, even more preferably from 40 % to 50 %.

[0060] The inventors surprisingly found that the use of even a small amount of an alkyne comonomer compound of formula (I) in the preparation of a modified polythiourethane material led to a material having an improved impact resistance, as compared to the pure polythiourethane material that suffers from a low impact resistance.

[0061] Without wishing to be bound by any theory, the inventors believe that yet acting as a crosslinking agent in the polymer network, the alkyne compound of formula (I) also introduces thioether bonds imparting more flexibility to the polymer network, as compared to a pure polythiourethane matrix without the alkyne co-monomer.

[0062] As evidenced by the experimental part, the use of an alkyne co-monomer compound of formula (I) for preparing the polymerizable composition in quantities satisfying the SH / alkyne and NCX / alkyne molar ratios according to the invention is beneficial to other thermomechanical properties of the optical material, i.e., increases its glass transition temperature and elastic modulus as compared to the pure polythiourethane matrix. However, below the SH / alkyne and NCX / alkyne molar ratios according to the invention, i.e., when a too high amount of alkyne co-monomer compound of formula (I) is employed for preparing the polymerizable composition, the glass transition temperature of the material is significantly decreased. Without wishing to be bound by any theory, the inventors believe that the glass transition temperature initially increases because of increased crosslinking brought by the alkyne co-monomer compound of formula (I), but a too high amount of this alkyne makes the glass transition temperature decrease again because the polymer network becomes increasingly mediated by thioether bonds, causing a network bond loosening.

[0063] According to the present invention, the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of SH / alkyne groups present in all said polymerizable compounds is higher than or equal to 7. Said molar ratio of SH / alkyne groups is preferably higher than or equal to 8, 9, 10 or 11 , and / or said molar ratio of SH / alkyne groups is preferably lower than or equal to 90, 85, 81 or 80. Those polymerizable compounds may be compounds of formula (I), which may be identical or different, polythiols, optional polymerizable compounds of other categories, etc.

[0064] According to the present invention, the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / alkyne groups present in all said polymerizable compounds is higher than or equal to 6, X being O or S. Said molar ratio of NCX / alkyne groups is preferably higher than or equal to 7, 8,

[0065] 9 or 10 and / or said molar ratio of NCX / alkyne groups is preferably lower than or equal to 90, 85, 80 or 79. Those polymerizable compounds may be compounds of formula (I), which may be identical or different, poly(iso)thiocyanates, optional polymerizable compounds of other categories, etc.

[0066] In one embodiment, when said molar ratio of NCX / alkyne groups is higher than or equal to 7, 8, 9 or 10, said molar ratio of SH / alkyne groups is respectively higher than or equal to 8, 9,

[0067] 10 or 11. In one embodiment, when said molar ratio of NCX / alkyne groups is lower than or equal to 90, 85, 80 or 79, said molar ratio of SH / alkyne groups is respectively lower than or equal to 90, 85, 81 or 80.

[0068] The molar ratios of reactive groups defined in relation to the polymerizable composition can be calculated from the amounts of all starting materials used to prepare the prepolymer and the polymerizable composition (polythiols, polyiso(thio)cyanates, polymerizable compounds of formula (I), etc.).

[0069] In one embodiment, the prepolymer having thiol end groups obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I) is such that the molar ratio of SH / alkyne groups for the mixture of polythiols and polymerizable compounds of formula (I) used for the preparation of said prepolymer is higher than or equal to 7, 8, 9, 10 or 11. Said molar ratio of SH / alkyne groups is preferably lower than or equal to 90, 85, 81 or 80.

[0070] In one embodiment, the prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, obtained from the reaction of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I) is such that the molar ratio of NCX / alkyne groups for the mixture of polyisocyanates or polyisothiocyanates and polymerizable compounds of formula (I) used for the preparation of said prepolymer is higher than or equal to 6, X being O or S, more preferably higher than or equal to 7, 8, 9 or 10. Said molar ratio of NCX / alkyne groups is preferably lower than or equal to 90, 85, 80 or 79.

[0071] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of (NCX groups + 2 alkyne groups) I (SH groups + OH, NH2 and / or NHR4groups that may be present in the compound of formula (I)) present in all said polymerizable compounds ranges from 0.9 to 1.1 , and is preferably 1 , X being O or S.

[0072] Indeed, a stoichiometric reaction between polyiso(thio)cyanates, polythiols and compounds of formula (I) requires the use of two equivalents of alkyne functions and one equivalent of NCX functions for three equivalents of (OH, SH, NH2 and NHR4functions) for preparing the polymerizable composition, when no other function reactive toward these functions is present.

[0073] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of (NCX groups + alkyne groups) I SH groups present in all said polymerizable compounds ranges from 0.9 to 1 .1 , X being O or S. When this simplified ratio is close to 1 , the polymerization reaction is generally close to balance, in terms of reactive functions.

[0074] In one embodiment, the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / SH groups present in all said polymerizable compounds ranges from 0.7 to 1.2, more preferably from 0.8 to 1 , X being O or S.

[0075] The compound of formula (I) is a heterodifunctional compound that contains at least two different reactive (polymerizable) functions, namely a Z group and an alkynylene -C=CH group.

[0076] The compound of formula (I) is defined as a compound comprising at least one alkyne bond. It preferably comprises one or two alkyne bonds, more preferably one. The compound of formula (I) is defined as a compound comprising at least one group selected from OH, SH, NH2 or NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group. It preferably comprises 1 or 2 groups selected from OH, SH, NH2 or NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, more preferably 1. The Z and Z’ groups of the compound of formula (I) are reactive groups that can take part to polymerization reactions with iso(thio)cyanate groups.

[0077] In one embodiment, the compound of formula (I) is such that the ratio of groups selected from OH, SH, NH2 or NHR4(R4being defined above) I alkyne groups per molecule of compound of formula (I) is equal to 1 or 2, preferably 1.

[0078] 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.

[0079] By "substituted alkyl" group 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 such as the trityl group (-CPha), the benzyl group or the 4-methoxybenzyl group, alkoxyalkyl groups, particularly dialkoxymethyl groups such as the diethoxymethyl or dimethoxymethyl groups, the groups CH2CO2R11, wherein R11represents an optionally substituted alkyl or aryl group.

[0080] 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 15 carbon atoms.

[0081] 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.

[0082] A (hetero)aryl group represents a heteroaryl or aryl group.

[0083] 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 aryl group is “arylene”, a divalent alkyl group is “alkylene”. Alkylene groups are connected to the rest of the molecule via two sp3carbon atoms. Arylene groups are connected to the rest of the molecule via two sp2carbon atoms.

[0084] Examples of alkylene groups include linear C1-C10 alkylene groups, for example a methylene group -CH2-, an ethylene group -CH2-CH2-, 1 ,3-propylene, a butylene or a hexylene group, especially 1 ,4-butylene and 1 ,6-hexylene and branched C3-C10 alkylene radicals such as

[0085] 1 .4-(4-methyl pentylene), 1 ,6-(2,2,4-trimethyl hexylene), 1 ,5-(5-methyl hexylene), 1 ,6-(6-methyl heptylene), 1 ,5-(2,2,5-trimethyl hexylene), 1 ,7-(3,7-dimethyl octylene), 2,2-(dimethylpropylene),

[0086] 1.5-pentylene, 1 ,1 -dimethylpentylene and 1 ,6-(2,4,4-trimethyl hexylene) radicals. Preferred cycloalkylene radicals include cyclopentylene and cyclohexylene radicals, optionally substituted especially by alkyl groups.

[0087] Examples of arylene groups include 2,4-tolylene, 2,6-tolylene, 2,4-naphthylene, 2,6- naphthylene, 1 ,5-naphthylene, 1 ,4-phenylene, 1 ,4-bisphenylene (-P-C6H4-P-C6H4-), 2-methyl-1 ,3- phenylene, 4-methyl-1 ,3-phenylene, tetramethylxylylene, 1 ,4-phenylene-methylene-1 ,4- phenylene (4,4-biphenylenemethylene).

[0088] In the present application, alkyl groups preferably comprise from 1 to 5 carbon atoms, more preferably from 1 to 4 carbon atoms, from 1 to 3 carbon atoms, or from 1 to 2 carbon atoms.

[0089] In one embodiment, R1= R2.

[0090] The group -R1-R2- defined in the present application preferably represents a linear alkylene group such as -(CH2)s- (thus forming a cyclohexyl group with the carbon atom connected to the alkyne bond) or -(CH2)4-.

[0091] The R1and R2groups preferably represent, independently of each other, a hydrogen atom or a substituted or unsubstituted alkyl group, the alkyl group being preferably a C1-C5 alkyl group, more preferably a C1-C2 alkyl group and ideally a methyl group.

[0092] In preferred embodiments of the invention, R1= R2= H, or R1= R2= CH3, or R1= H and R2= CH3, or R1= H and R2= 3-heptyl, or R1= H and R2= i-butyl.

[0093] A useful category of compounds of formula (I) comprises terminal alkynes, in which R3= H.

[0094] In one embodiment, said polymerizable compound is selected from the compounds of formula (IV): in which R1and R2are as defined above and preferably represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, and Z is as defined above and preferably represents OH, SH or NH2.

[0095] In one embodiment, said polymerizable compound is selected from the compounds of formula (II): in which R1and R2are as defined above and preferably represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group.

[0096] Specific examples of such compounds of formula (II) are shown hereunder:

[0097] Another useful category of compounds of formula (I) comprises those in which R3represents a group of formula:

[0098] R'1

[0099] Z' —

[0100] R'2in which R’1and R’2are as defined above and preferably represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group, Z’ represents OH, SH, NH2or NHR’4in which R’4represents a substituted or unsubstituted alkyl group or (hetero)aryl group.

[0101] In one embodiment, R1= R2and R’1= R’2. In another embodiment, Z = Z’.

[0102] The group -R’1-R’2- defined in the present application preferably represents a linear alkylene group such as -(CH2)s- (thus forming a cyclohexyl group with the carbon atom connected to the alkyne bond) or -(CH2)4-.

[0103] The R’1and R’2groups preferably represent, independently of each other, a hydrogen atom or a substituted or unsubstituted alkyl group, the alkyl group being preferably a C1-C5 alkyl group, more preferably a C1-C2 alkyl group and ideally a methyl group. In preferred embodiments of the invention, R’1= R’2= H, or R’1= R’2= CH3, or R’1= H and R’2= CH3, or R’1= H and R’2= i-butyl, or R1= R2= R’1= R’2= H, or R1= R2= R’1= R’2= CH3, or R1= R’1= H and R2= R’2= CH3, or R1= R’1= CH3and R2= R’2= i-butyl.

[0104] In one embodiment, said polymerizable compound is selected from the compounds of formula (V): in which R1, R2, R’1and R’2are as defined above and preferably represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group, and Z and Z’ are as defined above and preferably independently represent OH, SH or NH2.

[0105] In one embodiment, said polymerizable compound is selected from the compounds of formula (Ila):

[0106] R'1R1

[0107] HO - = - OH (Ila)

[0108] R'2R2in which R1, R2, R’1and R’2are as defined above and preferably represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group.

[0109] Specific examples of such compounds of formula (Ila) are shown hereunder:

[0110] Other examples of useful polymerizable compounds of formula (I) include SH and NH2 analogues of the compounds of formulae (II) and (Ila) such as propargylamine or propargyl thiol.

[0111] The polymerizable compounds of general formulae (I), (II) (Ila), (IV) and (V) are commercially available or can be easily synthesized from widely available and relatively cheap raw materials, such as propargyl alcohol, propargyl chloride, 1-ethynyl-1 -cyclohexanol, 3-butyne- 2-ol, 2-methyl-3-butyn-2-ol, 2-butyne-1 ,4-diol, 3-hexyne-2,5-diol, propargyl thiol, propargyl amine, etc., through chemical reactions well known to those skilled in the art. The widespread use of these raw materials used to synthesize the monomers of the present invention enables very competitive cost in regard of the refractive index achieved. 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 prepolymers or oligomers may be used. The polythiol may be any suitable polythiol having two or more, preferably two, three or four thiol functions.

[0112] By prepolymer, it is meant a polymer or oligomer comprising prepolymer molecules. By prepolymer 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.

[0113] In one embodiment of the invention, said polythiol is a compound of formula:

[0114] R5(SH)n1 (III) wherein n1 represents an integer ranging from 2 to 6 and R5represents an aliphatic, alicyclic, heterocyclic or aromatic group.

[0115] 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), dipentaerythritol hexakis(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 of formula (Via), 4,8- dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane of formula (Vila), 4,7- dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercaptomethyl-1 ,11- dimercapto-3,6,9-trithiaundecane, 2,5-bis (mercaptomethyl)-1 ,4-dithiane, and 2,5-bis[(2- mercaptoethyl)thiomethyl]-1 ,4-dithiane, 1-(T-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, 1 ,2-bis(2’-mercaptoethylthio)-3-mercaptopropane, tris[2-(3- mercaptopropionyloxy)ethyl] isocyanurate of formula (Villa), 2-mercaptoethyl 2-mercaptoacetate of formula (IX), 2-mercaptoethyl 3-mercaptopropionate, 1 ,1 ,3,3-tetrakis (mercaptomethylthio) propane, 4,6-bis (mercaptomethylthio)-1 ,3-dithiane, 1 , 1 ,2,2-tetrakis (mercaptomethylthio) ethane, 3-mercaptomethyl-1 ,5-dimercapto-2,4-dithiapentane, tris (mercaptomethylthio) methane, ethylene glycol bis (3-mercaptopropionate), butylene glycol bis (3-mercaptopropionate), 2-(2,2- bis (mercaptomethylthio) ethyl)-1 ,3-dithietane.

[0116] Further examples of polythiols are shown in the formulae below or can be found in WO 2014 / 133111 , EP 394495, US 4775733 or EP 1877839:

[0117] C2H5C(CH2COOCH2CH2SH)3

[0118] In one embodiment of the invention, said polythiol is selected from the group consisting of pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), tris(3- mercaptopropionate) trimethylolpropane, tris(2-mercaptoacetate) trimethylolpropane, 2,3-bis((2- mercaptoethyl)thio)-1 -propanethiol, ethylene glycol bis (3-mercaptopropionate), butylene glycol bis (3-mercaptopropionate), 2-mercaptoethyl 2-mercaptoacetate, 2-mercaptoethyl 3- mercaptopropionate, 5,7-dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 4,7- dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 4,8-dimercaptomethyl-1 ,11- dimercapto-3,6,9-trithiaundecane, 2,5-bis (mercaptomethyl)-1 ,4-dithiane, bis (mercaptoethyl) sulfide, 1 ,1 ,3,3-tetrakis (mercaptomethylthio) propane, 4,6-bis (mercaptomethylthio)-1 ,3-dithiane, 2-(2,2-bis (mercaptomethylthio) ethyl)-1 ,3-dithietane, 1 ,1 ,2,2-tetrakis (mercaptomethylthio) ethane, 3-mercaptomethyl-1 ,5-dimercapto-2,4-dithiapentane, tris (mercaptomethylthio) methane, dipentaerythritol hexakis(3-mercaptopropionate), tris[2-(3-mercaptopropionyloxy)ethyl] isocyanurate, and ethanedithiol.

[0119] The most preferred polythiols are 2-mercaptoethyl 2-mercaptoacetate of formula (IX), pentaerythritol tetrakis (3-mercaptopropionate) of formula (X) and 2,3-bis((2-mercaptoethyl)thio)- 1 -propanethiol of formula (Via). Especially, a mixture of 2-mercaptoethyl 2-mercaptoacetate and 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol can be used.

[0120] In one embodiment, a mixture of at least two different polythiols is used, having preferably a different number of thiol groups, for example a mixture of two polythiols. In some embodiments, the polymerizable composition comprises at least one polythiol having three SH groups and at least one polythiol having four SH groups. In one embodiment, the polymerizable composition comprises a mixture of pentaerythritol tetrakis (3-mercaptopropionate) and 2,3-bis((2- mercaptoethyl)thio)-1 -propanethiol.

[0121] By adjusting the respective ratios of polythiols, it is possible to adjust the refractive index and the mechanical properties of the final polymer.

[0122] By polyisocyanate, it is meant any compound comprising at least two isocyanate groups, in other words diisocyanates, triisocyanates, etc. Polyisocyanate prepolymers may be used. The polyisocyanate may be any suitable polyisocyanate having two or more, preferably two or three isocyanate functions.

[0123] The polyisocyanates may be selected from aliphatic, aromatic, cycloaliphatic or heterocyclic polyisocyanates and mixtures thereof.

[0124] Polyisothiocyanates are defined in the same manner as polyisocyanates above, by replacing the “isocyanate” group by the “isothiocyanate” group.

[0125] In one embodiment of the invention, said polyisocyanate or polyisothiocyanate is a compound of formula (VI):

[0126] R6(NCX)n2(VI) wherein X represents O or S, n2 represents an integer ranging from 2 to 6 and R6represents an aliphatic, alicyclic, heterocyclic or aromatic group.

[0127] The preferred polyisocyanate or polyisothiocyanate compounds are those having the formulae: wherein R1is independently H or a C1-C5 alkyl group, preferably CH3 or C2H5;

[0128] R2is H, a halogen, preferably Cl or Br, or a C1-C5 alkyl group, preferably CH3 or C2H5;

[0129] 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.

[0130] The polyisocyanates of the invention are preferably diisocyanates, such as arylene 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, norbornane diisocyanate, ethylene diisocyanate, dodecane-1 ,12-diisocyanate, cyclobutane- 1,3-di isocyanate, cyclohexane- 1,3- diisocyanate, cyclohexane-1 ,4-diisocyanate, hexahydrotoluene-2,4-diisocyanate, tetramethylxylylene diisocyanate, hexahydrotoluene-2,6-diisocyanate, perhydro diphenylmethane-2,4'-diisocyanate, 4,4'-dicyclohexylmethanediisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, 2,5- bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane 2,6-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, 1 ,5-naphtalene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate trimer, 1,6- hexamethylene diisocyanate trimer, and mixtures thereof.

[0131] Further polyiso(thio)cyanates suitable for the present invention are described in detail in WO 98 / 37115, WO 2014 / 133111 or EP 1877839.

[0132] 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.

[0133] The polymerizable composition 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 catalysts / polymerization initiators, photochromic agents, UV absorbers, perfumes, deodorants, 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, inhibitors, anti-yellowing agents and mold release agents.

[0134] UV absorbers are frequently incorporated into optical materials 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 420-450 nm. Said UV absorbers both protect the user’s eye from UV light and the optical 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.

[0135] 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 generally present in an amount ranging from 0.05 to 4 % by weight relative to the optical material total weight (or per 100 parts by weight of the polymerizable compounds present in the composition or relative to the weight of the optical material composition), preferably from 0.1 to 3 % by weight, more preferably from 0.1 to 2 % by weight.

[0136] 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 4975328 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 polymerizable composition (or relative to the weight of the optical material composition).

[0137] The optical material is a dual cure system in the sense that it is obtained from both thermally polymerizable and photopolymerizable compounds.

[0138] In one embodiment, the optical material polymerizable composition contains (or is prepared using) at least one system for initiating and / or accelerating the polymerization reaction (initiator). The polymerization initiating system can comprise at least one (thermal) catalyst or at least one photochemical polymerization initiating agent (photoinitiator) or alternatively, a mixture of (thermal) and photochemical polymerization initiating agents. In a preferred embodiment, the polymerizable composition contains (or is prepared using) both a photoinitiator and a (thermal) catalyst.

[0139] A polymerization initiating system can be used to initiate and / or accelerate the polymerization reaction forming the prepolymer having thiol end groups or the prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, which is obtained from at least one polymerizable compound of formula (I) and either at least one polythiol or at least one polyisocyanate or polyisothiocyanate, and can still be present in the polymerizable composition comprising the prepolymer and the complementary polymerizable compound.

[0140] A polymerization initiating system can also be used in the polymerizable composition to initiate and / or accelerate the polymerization reaction between the prepolymer and the complementary polymerizable compound.

[0141] A photoinitiator represents a molecule that absorbs light and generates reactive species (ions or radicals) that initiate a chemical reaction or transformation. In the present invention, a photoinitiator is preferably used to promote the reaction between thiol groups and alkyne groups (thiol-yne reaction).

[0142] Photoinitiators can be selected for example from haloalkylated aromatic ketones such as chloromethylbenzophenones, benzoin and benzoin alkyl ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, benzoin, dialkoxyacetophenones such as diethoxyacetophenone and 2,2-dimethoxy-2- phenylacetophenone, benzylideneacetophenone, hydroxy ketones such as (1-[4-(2- hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1 -propan-1 -one) (Irgacure® 2959 from CIBA), 2,2-di- sec-butoxyacethophenone, 2,2-diethoxy-2-phenyl-acetophenone, 1 -hydroxy-cyclohexyl-phenyl- ketone (Irgacure® 184 from CIBA) and 2-hydroxy-2-methyl-1-phenylpropan-1-one (such as Darocur® 1173 sold by CIBA), alpha amino ketones, particularly those containing a benzoyl moiety, otherwise called alpha-amino acetophenones, for example 2-methyl 1-[4-phenyl]-2- morpholinopropan-1-one (Irgacure® 907 from CIBA), (2-benzyl-2-dimethyl amino-1-(4- morpholinophenyl)-butan-1-one (Irgacure® 369 from CIBA), monoacyl and bisacyl phosphine oxides and sulphides, such as phenylbis(2,4,6-trimethylbenzoyl)-phosphine oxide (Irgacure® 819 sold by CIBA, and Irgacure® 2022, which is a blend containing Irgacure® 819 and Darocur® 1173), 2, 4, 6, -trimethylbenzoylethoxydiphenyl phosphine oxide, triacyl phosphine oxides, 2,2'-bis(2- chlorophenyl)-4,4',5,5'-tetraphenyl-1 ,2'-biimidazole and mixtures thereof.

[0143] Free radical initiators such as peroxides and azo compounds, either thermally or photocatalyzed, can also be used, as well as Lewis acids, such as triarylsulfonium hexafluoroantimonate salts or diaryliodonium salts.

[0144] Photoinitiators shall be used in the polymerizable composition or to prepare the prepolymer according to the invention in an amount sufficient to promote the polymerization reaction. They are generally present in an amount ranging from 0.05 to 10 % by weight, preferably from 0.2 % to 5 %, and more preferably from 0.25 to 2 % by weight, relative to the total weight of polymerizable compounds present in the polymerization composition or used for preparing the prepolymer according to the invention, or relative to the total weight of polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition.

[0145] In the present invention, a thermal catalyst promotes the reaction between iso(thio)cyanate groups and groups selected from thiol, hydroxyl, amino and NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group (thiourethanization reaction). This condensation reaction is favored by heat. In one embodiment, the (thermal) catalyst is selected from tin compounds such as alkyltins, alkyltin oxides, metal coordination complexes such as cobalt naphthenate and amines or nitrogen-containing basic compounds. Several catalysts can be combined in the present polymerizable composition.

[0146] Tin catalysts may be chosen from the group consisting of tin octylate, stannous octoate (tin 2-ethylhexanoate), dibutyltin diacetate, dibutyltin dichloride, dimethyltin dichloride, dibutyltin dilaurate, dibutyltin mercaptide, dibutyltin dimaleate, dimethyltin diacetate, dimethyltin dilaurate, dimethyltin mercaptide, dimethyltin dimaleate, triphenyltin acetate, triphenyltin hydroxide.

[0147] Amine or nitrogen-containing basic catalysts may be chosen from aliphatic or aromatic tertiary amines preferably containing a supplemental heteroatom in the ring or functional groups having a positive inductive and / or positive mesomeric effect (for example, alkyl groups or amino groups). Examples include 1 ,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine, quinuclidine, 2,2'-dimorpholinodiethylether, N,N-dimethylpiperazine, 1 -methylimidazole, 2-methyl-1- vinylimidazole, 1 -allylimidazole, 1 -phenylimidazole, 1 ,2,4,5-tetramethylimidazole, 1 (3- aminopropyl)imidazole, 4-dimethylaminopyridine, 4-pyrrolidino-pyridine, 4-morpholinopyridine, 4- methylpyridine, 3,5-lutidine, N-dodecyl-2-methylimidazole, triazines such as tris(dimethylaminopropyl) hexahydrotriazine, dimethylbenzylamine, N,N-dimethylcyclohexyl amine, bis-dimethylamino-ethylether and pentamethyl diethylenetriamine. p_l_ _

[0148] In another embodiment, the catalyst is a salt compound of formula MmYn, wherein Mp+is a cation of valence p selected from the group consisting of alkaline metal cations, alkaline earth metal cations, transition metal cations and ammonium groups of formula NR4+in which R is an alkyl group having preferably from 1 to 10 carbon atoms, Y’ is an anion such that the corresponding acid YH has a pKa fulfilling the condition 0.5 < pKa < 14, m, n and p being integers such that n = m x p.

[0149] The preferred metallic cations of the salts are Li+, Na+, K+, Cs+, Mg2+, Ca2+, Mn2+, Ag+, Ba2+and Al3+. The particularly preferred metallic cations are Li+, Na+and K+due to their absence of color and solubility in the composition. Transition metals are less preferred because their salts can lead to colored compositions and therefore colored polymerized resins. In one embodiment, the method according to the invention does not use a catalyst containing tin.

[0150] The preferred NR groups are those in which R is a Ci-Cs alkyl group and more preferably, a methyl, ethyl, propyl, butyl or hexyl group.

[0151] Preferably, Y’ is an anion such that the corresponding acid YH which fulfills the condition 0.5 < pKa < 10 and more preferably 0.5 < pKa < 8. 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.

[0152] Preferably, the anion Y’ is selected from the group consisting of thiocyanate, carboxylate anions, thiocarboxylate anions, acetylacetonate, diketone anions, acetoacetic ester, malonic ester anions, cyanoacetic ester anions, ketonitrile anions, malononitrile anion and anions of formula RS' wherein R is a substituted or non-substituted alkyl group having preferably from 1 to 10 carbon atoms or an aryl group having preferably from 6 to 12 carbon atoms. The preferred anions Y’ are SCN acetylacetonate, acetate, thioacetate, formate and benzoate. The preferred salt catalyst is potassium thiocyanate KSCN.

[0153] Such salt catalysts are described in more detail in the application US 2007 / 202265. They are preferably used in combination with electron-donor compounds also described in US 2007 / 202265, such as crown ethers, typically 18-crown-6.

[0154] The (thermal) catalyst shall be used in the polymerizable composition or to prepare the prepolymer according to the invention in an amount sufficient to promote the polymerization of the mixture. They are generally present in an amount ranging from 0.01 % to 5 % by weight with respect to the total weight of polymerizable compounds present in the composition, or used for preparing the prepolymer according to the invention, or relative to the total weight of polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition, more preferably from 0.02 to 2% by weight. A too high amount of catalyst should also be avoided to prevent premature gelation of the polymerizable mixture before it is introduced in the mold.

[0155] The polymerizable compositions can comprise a solvent for promoting the dissolution of additives, such as catalysts. Any polar organic solvent can be used such as acetonitrile, tetra hydrofuran, dioxane, ethanol, 2-mercaptoethanol, acetone, or 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 composition and preferably from 0 to 0.5% by weight, to avoid haze and bubbling.

[0156] The invention also relates to an optical material obtained by polymerization of a polymerizable composition as described above. The optical material combines thioether and thiourethane functionalities, and optionally urethane (when Z or Z’ = OH) and / or urea (when Z or Z’ = NH2 or NHR4as defined above) functionalities, depending on the structure of the compound of formula (I). Thioether bonds result from the reaction of alkyne groups with thiols, thiourethane bonds result from the reaction of iso(thio)cyanate groups with thiols, urethane bonds result from the reaction of iso(thio)cyanate groups with alcohols, while urea bonds result from the reaction of iso(thio)cyanate groups with amines.

[0157] The optical material according to the invention is distinguishable from related polythiourethane-based optical materials obtained in the prior art by means of its improved thermomechanical properties (impact resistance, elastic modulus, glass transition temperature...) and lower yellowness index, as demonstrated in the experimental part, and also by its improved conversion rate of monomers.

[0158] The conversion rate of polyisocyanate or polyisothiocyanate compounds in the optical material according to the invention is preferably higher than or equal to 95 %, more preferably higher than or equal to 98 %. The conversion rate of such compounds can be calculated by methods well known to the skilled person, such as by studying the relative intensitiy of NCO / NCS peak on the solid lens to the monomer by infrared spectroscopy. As an example, a calculation of the relative intensity of NCO / CH peak on the solid lens to the monomer by infrared spectroscopy will be detailed in the experimental part with reference to figures 1 and 2.

[0159] A calculation of the % NCO conversion (or conversion rate) is described hereafter.

[0160] The conversion is linked to the completion of polymerization which is calculated by comparing the relative NCO value of lens with that of monomers.

[0161] PkNCO and PkCH2 are measured on the FTIR spectrum of an initial monomer composition (including isocyanate(s) and thiol(s) (as shown on a typical spectrum on Figure 1) and on the FTIR spectrum of the corresponding polymer composition (as shown on a typical spectrum on Figure 2) after the corresponding reaction time.

[0162] Pk is the Peak Intensity corresponding to the NCO peak or CH2 peak minus the %T at the baseline of the corresponding peak.

[0163] Then the ratio NCO relative to CH2 internal peak can be calculated according to the following equation:

[0164] %NC0 conversion = t oo - %KO nsittie

[0165] The invention further relates to a prepolymer having thiol end groups obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I) as described above, wherein the molar ratio of SH / alkyne groups for the mixture of polythiols and polymerizable compounds of formula (I) used for the preparation of said prepolymer is higher than or equal to 7. Preferred SH / alkyne groups molar ratios described above are also applicable to this prepolymer.

[0166] The invention further relates to a prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S obtained from the reaction of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I) as described above, wherein the molar ratio of NCX / alkyne groups for the mixture of polyisocyanate or polyisothiocyanate and polymerizable compounds of formula (I) used for the preparation of said prepolymer is higher than or equal to 6. Preferred NCX / alkyne groups molar ratios described above are also applicable to this prepolymer. The invention further relates to a process for the preparation of an optical material as described above, comprising the following steps 1), 2), and 3) or T), 2’), and 3’):

[0167] 1) Providing a first component comprising at least one prepolymer having thiol end groups obtained by polymerization (preferably photopolymerization) of a mixture of at least one polythiol and at least one polymerizable compound of formula (I) as described above in the presence of at least one initiator, preferably a photoinitiator,

[0168] 2) providing a second component comprising at least one polyisocyanate or polyisothiocyanate,

[0169] 3) Mixing together the first and second components to form a polymerizable composition, and thermally polymerizing said polymerizable composition in the presence of at least one catalyst to obtain the optical material, or:

[0170] T) Providing a first component comprising at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, obtained by thermal polymerization of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I) as described above in the presence of at least one catalyst,

[0171] 2’) Providing a second component comprising at least one polythiol,

[0172] 3’) Mixing together the first and second components to form a polymerizable composition, and polymerizing (preferably photopolymerizing) said polymerizable composition in the presence of at least one initiator (preferably a photoinitiator) to obtain the optical material, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds mixed with said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of SH / alkyne groups present in all said polymerizable compounds is higher than or equal to 7, and the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds mixed with said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / alkyne groups present in all said polymerizable compounds is higher than or equal to 6, X being O or S.

[0173] Compared to prior art processes which use only iso(thio)cyanate, alkyne or thiol monomers, the present invention uses at least one prepolymer, which provides some advantages. As demonstrated by the experimental part, the optical material obtained by the process of the present invention starting from a prepolymer and the complementary polymerizable compound has a much lower yellowness index than the corresponding optical material obtained by in situ mixing all the precursor monomers in the same amounts.

[0174] The process preferably involves casting polymerization.

[0175] The mixing of the different constituents of the polymerizable composition can be performed by any known mixing technique such as those mentioned in US 5973098, preferably by introducing the constituents in a small reactor chamber and then mixing with a screw mixer. In one embodiment, one or more of the additives mentioned above, such as an initiator, are added to first component (comprising the prepolymer) prior to the mixing with second component (comprising the complementary polymerizable compound). In another embodiment, one or more of the additives mentioned above are added to the mixture of the polymerizable compound of formula (I) and either the polythiol or the polyisocyanate or polyisothiocyanate, i.e., during the preparation of the prepolymer (component A or B). In another embodiment, one or more of the additives mentioned above are added during step 3) or 3”) of mixing together the first and second components, or prior to step 3) or 3”).

[0176] The optical material is obtained by a sequential process in which a prepolymer is first formed from the compound of formula (I) and then reacted with a complementary polymerizable compound, which is either a polythiol or a poly(iso)thiocyanate depending on the end groups of the prepolymer.

[0177] A molding cavity of a casting mold assembly having any desirable shape can then be filled with the polymerizable composition.

[0178] The casting mold assembly generally comprises two mold parts defining two molding surfaces that cooperate to form a molding cavity when moved from an open position to a closed position. Each of the molding surfaces can be concave, convex, or planar, depending on the desired article shape. The molding surface can be convex, e.g., to form a concave substrate surface, or concave, e.g., to form a convex substrate surface.

[0179] 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 an adhesive tape.

[0180] An annular closure member can be disposed around the periphery of the two mold pieces and attached to them. The conventional way to fill such a two-piece mold is by causing the (liquid) optical material composition to flow into the molding cavity through a casting opening provided for this purpose in the closure member. In at least a partly automated process, the molding cavity to be filled is vertically aligned with a filling device that is adapted to deliver a particular quantity of molding material through a nozzle.

[0181] 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 assembly.

[0182] After pouring the composition in the casting mold assembly, preferably a lens casting mold assembly, polymerization is triggered.

[0183] The thiol-yne reaction occurs upon irradiation. This is the main reaction occurring during step 3’) of the present process. The thiourethanization reaction (and possibly urea and / or urethane bond formation) occurs upon heating. This is the main reaction occurring during step 3) of the present process.

[0184] Thiol / alcohol / amine-iso(thio)cyanate condensations on one hand and thiol-yne condensations on the other hand can proceed orthogonally, especially when a combination of a thermal catalyst and a photoinitiator to polymerize the polymerizable composition. Photopolymerization of a polymerizable composition (forming the prepolymer or the optical material) can be performed by irradiating the composition with radiation, preferably ultraviolet light. Preferably, UV light wavelength ranges from 320 to 390 nm. UV light intensity typically ranges from 40 to 90 mW / cm2and the total exposure time to UV light, either in one shot or several shots, preferably ranges from 15 to 1650 seconds, more preferably from 20 to 600 seconds.

[0185] Thermal polymerization of a polymerizable composition (forming the prepolymer or the optical material) can be performed in an oven or a heating device immersed in water according to a predetermined temperature program to cure the resin. Thermal polymerization includes induction and infrared heating. The curing temperature generally ranges from 60°C to 140°C. The curing time is preferably lower than or equal to 25, 20, 10 or 5 hours, more preferably lower than or equal to 4, 3 or 2 hours. As used herein, curing refers to a chemical process of converting monomers or oligomers into a polymer of higher molar mass and then into a network.

[0186] The resin molded product may then be annealed, if necessary, at a temperature preferably ranging from 100°C to 150°C.

[0187] Thereafter, the mold assembly is withdrawn from the heating source, the annular closure member is removed and the polymerized optical material can be recovered after disassembly of the mold parts.

[0188] 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.

[0189] In some applications, it is preferred that the main surface of the optical material be coated with one or more functional coating(s) to improve the optical and / or mechanical properties. The term “coating” is understood to mean any layer, layer stack or film which may be in contact with the substrate and / or with another coating, for example a sol-gel coating or a coating made of an organic resin. A coating may be deposited or formed through various methods, including wet processing, gaseous processing, and film transfer. These functional coatings classically used in optics may be, without limitation, an impact-resistant and / or adhesion primer, an abrasionresistant and / or scratch-resistant coating, an anti refl ection coating, a polarized coating, a photochromic coating, or an antistatic coating, or a stack made of two or more such coatings, especially an impact-resistant primer coating coated with an abrasion and / or scratch-resistant coating.

[0190] 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. The percentages given in the tables are weight percentages.

[0191] Examples

[0192] The polymerizable heterodifunctional alkyne compounds according to the invention can be selected, without limitation, from the compounds of formulae:

[0193] Optical substrates were prepared by polymerization of a heterodifunctional alkyne monomer (propargyl alcohol, CAS No. 107-19-7), at least one polythiol monomer and a polyisocyanate monomer (isophorone diisocyanate, CAS No. 4098-71-9) in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone, CAS No. 24650-42-8, 0.25 % by weight) and a thermal catalyst (dimethyl tin dichloride, CAS No. 753-73-1 , 0.2 % by weight). The polymerizable composition also contained Zelec UN® as a mold release agent (0.15 % by weight).

[0194] The following polythiol monomers were used: 2,3-bis((2-mercaptoethyl)thio)-1- propanethiol (CAS No. 131538-00-6) and / or pentaerythritol tetrakis (3-mercaptopropionate) (CAS No. 7575-23-7).

[0195] Cleaned convex and concave piano glass molds of high refractive index having 75 mm diameter were assembled with a tape. A center thickness adjustment was made to obtain 1.1 mm thick samples. In a Duran bottle with a magnetic stirrer the thermal catalyst, the photoinitiator and alkyne monomer of formula (I) were dissolved in the polythiol monomer(s) at room temperature for 30 minutes. The prepolymerization reaction was carried out by UV-irradiation (365 nm) for 30 seconds (examples 1 to 4, C1 to C3) or 180 seconds (examples 5 to 7, C4) in UV-LED curing oven (Height-LED HTBX-II). The thermal catalyst was added as this initial stage to make easier its solubilization.

[0196] The resulting prepolymer having thiol end groups was mixed with the polyisocyanate monomer and the mold release agent. The composition was allowed to degas for 10-30 minutes to avoid bubbles in the final material.

[0197] The assembled molds were filled with the above prepared polymerizable composition using a cleaned syringe, and the polymerization reaction was carried out by thermal curing (100°C, 2h for all examples except for examples C4, 5-7: 120°C, 10h, to complete polymerization, by placing the assembled molds in a convection oven (Hot-Air oven, model B:121218B, Reliance tech-service Co, LTD). .

[0198] The molds were removed from the oven and allowed to cool at room temperature for 10 minutes, and then disassembled when the surface temperature of the molds was < 50°C, to obtain lenses comprising a body of a thermoset material.

[0199] In comparative example 1 (noted C1), no alkyne monomer was used. Isophorone diisocyanate being difunctional and pentaerythritol tetrakis (3-mercaptopropionate) tetrafunctional, the NCO / SH molar ratio of 1 :1 used indicates that 0.5 mol of the latter was used for 1 mol of the former (see § 3).

[0200] 2. Testing methods

[0201] The following test procedures were used to evaluate the optical articles prepared according to the present invention. They were obtained from consolidation of 5 different casting runs.

[0202] The thermal and mechanical properties of the lenses (glass transition temperature Tg and modulus of elasticity E) 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. 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 %.

[0203] The impact resistance of the 75 mm diameter piano lenses (center thickness: 1.1 mm) was evaluated according to the FDA drop ball test for ophthalmic glasses (ANSI Z87.1-1989 standard). This test consists in dropping a steel ball of 16 g from a height of 127 cm on the center of the convex face of the lens, which corresponds to an energy of 200 mJ. The lens successfully passed the test when the lens is neither broken nor presents star-shaped cracks. Impact tests were performed on at least four independent casting runs to ensure reproducibility.

[0204] 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 Cl E tristimulus values X, Y, Z such as described in the standard ASTM E 313-05, through reflection measures, with the front (convex) side of the lens facing the detector and light incoming on said front side. This way of measuring Yi, from an observer’s view angle, is the closest to the actual wearing situation.

[0205] 3. Optical articles prepared and characterizations

[0206] The tables hereunder indicate the different monomer formulations prepared and the thermomechanical properties of the resulting polymer. NCO / SH, NCO / alkyne and SH / alkyne are molar ratios of reactive functions introduced to prepare the prepolymer and polymerizable composition. Polyisocyanate / Alkyne compound (I) and Polythiol / Alkyne compound (I) are molar ratios of monomers introduced to prepare the prepolymer and polymerizable composition. SH functions were used in an amount balancing the amount of NCO + alkyne functions. a) Results with the polythiol pentaerythritol tetrakis (3-mercaptopropionate)

[0207] The optical materials according to the invention successfully passed the FDA impact resistance test at an amount of alkyne component as low as 0.3 % by weight, while keeping very good optical qualities such as low visual haze or no visual haze. As a comparison, the optical material of comparative example 1 (devoid of alkyne monomer) did not pass the impact resistance test.

[0208] The presence of the alkyne component improved or maintained the glass transition temperature of the resulting polymer at a high level (89-94°C), as compared to comparative example 1 (92°C). However, when the amount of alkyne modifier was too high (comparative examples 2 and 3), the glass transition temperature of the resulting polymer dropped significantly (70-79°C).

[0209] The introduction of the alkyne compound of formula (I) into the polythiourethane matrix also improved the elastic modulus of the resulting polymer, as compared to the pure polythiourethane matrix of comparative example 1. b) Results with a mixture of polythiols: 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol (polythiol 1) and pentaerythritol tetrakis (3-mercaptopropionate) (polythiol 2) A similar trend was observed in examples 5-7 on one hand and examples 1-4 on the other hand concerning the effect on thermomechanical properties (modulus improvement) of alkyne addition

[0210] 4. Comparison of the polymerization process using a prepolymer with the polymerization process starting from monomers

[0211] Additional experiments were performed by changing the polymerization process to show the benefit on yellowness index of forming the optical material from a reaction of the prepolymer with the polyisocyanate monomer rather than from the three monomers.

[0212] Optical materials were prepared by a one-pot reaction of the three monomers (polyisocyanate, polythiol, alkyne compound of formula (I)) using the same amounts of monomers as comparative examples 1-3 and examples 1-4.

[0213] The one-pot preparation process was as follows. In a Duran bottle with a magnetic stirrer, the polyisocyanate monomer and alkyne monomer of formula (I) were mixed with the thermal catalyst, the photoinitiator and the mold release agent. The solution was homogenized by stirring for 5 minutes. After that, the reaction was cooled at 20-22°C, and the polythiol monomer was added. The composition was then mixed and allowed to degas for 30 minutes to avoid bubbles in the final material. Degassing was continued for 5 minutes, without stirring. The assembled molds were filled with the above prepared polymerizable composition using a cleaned syringe, and the polymerization reaction was carried out by UV-irradiation and then by thermal curing under the same conditions as comparative examples 1-3 and examples 1-4.

[0214] The table below shows that the optical material obtained by the process of the present invention starting from a prepolymer and the complementary polymerizable compound has a much lower yellowness index than the corresponding optical material obtained by in situ mixing all the precursor monomers.

Claims

Claims1 . A polymerizable composition comprising: a) at least one polyisocyanate or polyisothiocyanate and a component B comprising at least one prepolymer having thiol end groups, said component B being obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I), or b) at least one polythiol and a component A comprising at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, said component A being obtained from the reaction of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I),in which R1and R2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group, Z represents OH, SH, NH2 or NHR4in which R4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, and R3represents a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or a group or formula:R'1Z' —R'2in which R’1and R’2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R’1and R’2, taken together, form a divalent group of formula -R’1-R’2-, in which -R’1-R’2- represents a substituted or unsubstituted alkylene group, Z’ represents OH, SH, NH2 or NHR’4in which R’4represents a substituted or unsubstituted alkyl group or (hetero)aryl group, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of SH / alkyne groups present in all said polymerizable compounds is higher than or equal to 7, and the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / alkyne groups present in all said polymerizable compounds is higher than or equal to 6, X being O or S.

2. The polymerizable composition of claim 1 , wherein said polymerizable compound is selected from the compounds of formula (II):in which R1and R2represent, independently of each other, a hydrogen atom, a substituted or unsubstituted alkyl group, an (hetero)aryl group, or R1and R2, taken together, form a divalent group of formula -R1-R2-, in which -R1-R2- represents a substituted or unsubstituted alkylene group.

3. The polymerizable composition of claim 1 , wherein said polymerizable compound is selected from the compounds of formulae:

4. The polymerizable composition of any one of the preceding claims, wherein the polymerizable composition is obtained from polymerizable compounds such that said compounds of formula (I) represent from 0.15 % to 4 % by weight relative to the total weight of polymerizable compounds used to prepare the prepolymer and polymerizable compounds added to said prepolymer in the polymerizable composition.

5. The polymerizable composition of any one of the preceding claims, wherein said polythiol is a compound of formula: R5(SH)ni(III) wherein n1 represents an integer ranging from 2 to 6 and R5represents an aliphatic, alicyclic, heterocyclic or aromatic group.

6. The polymerizable composition of any one of the preceding claims, wherein said polythiol is selected from the group consisting of pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), tris(3-mercaptopropionate) trimethylolpropane, tris(2- mercaptoacetate) trimethylolpropane, 2, 3-bis((2-mercaptoethyl)thio)-1 -propanethiol, ethylene glycol bis (3-mercaptopropionate), butylene glycol bis (3-mercaptopropionate), 2-mercaptoethyl 2-mercaptoacetate, 2-mercaptoethyl 3-mercaptopropionate, 5,7-dimercaptomethyl-1 ,11- dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 4,8-dimercaptomethyl-1 ,11-dimercapto-3,6,9-trithiaundecane, 2,5-bis (mercaptomethyl)-1 ,4- dithiane, bis (mercaptoethyl) sulfide, 1 , 1 ,3,3-tetrakis (mercaptomethylthio) propane, 4,6-bis (mercaptomethylthio)-1 ,3-dithiane, 2-(2,2-bis (mercaptomethylthio) ethyl)-1 ,3-dithietane, 1 , 1 ,2,2- tetrakis (mercaptomethylthio) ethane, 3-mercaptomethyl-1 ,5-dimercapto-2,4-dithiapentane, tris(mercaptomethylthio) methane, di pentaerythritol hexakis(3-mercaptopropionate), tris[2-(3- mercaptopropionyloxy)ethyl] isocyanurate, and ethanedithiol.

7. The polymerizable composition of any one of the preceding claims, wherein said polyisocyanate or polyisothiocyanate is a compound of formula (VI):R6(NCX)n2(VI) wherein X represents O or S, n2 represents an integer ranging from 2 to 6 and R6represents an aliphatic, alicyclic, heterocyclic or aromatic group.

8. The polymerizable composition of any one of the preceding claims, wherein said polyisocyanate or polyisothiocyanate is selected from the group consisting of 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, ethylene diisocyanate, dodecane-1 ,12- diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane- 1,3-di isocyanate, cyclohexane-1,4- diisocyanate, hexahydrotoluene-2,4-diisocyanate, tetramethylxylylene diisocyanate, hexahydrotoluene-2,6-diisocyanate, perhydro diphenylmethane-2,4'-diisocyanate, 4,4'- dicyclohexylmethanediisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, 2,5-bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane 2,6- bis(isocyanatomethyl)bicyclo-[2.2.1]-heptane, 1,5-naphtalene diisocyanate, pentamethylene diisocyanate, isophorone diisocyanate trimer and 1,6-hexamethylene diisocyanate trimer.

9. The polymerizable composition of any one of the preceding claims, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of (NCX groups + alkyne groups) I SH groups present in all said polymerizable compounds ranges from 0.9 to 1.1 , X being O or S.

10. The polymerizable composition of any one of the preceding claims, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds added to said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / SH groups present in all said polymerizable compounds ranges from 0.7 to 1.2, X being O or S.

11. An optical material obtained by polymerization of a polymerizable composition according to any one of the preceding claims.

12. The optical material of claim 11 , further defined as the substrate of an optical lens.

13. The optical material of claim 12, further defined as having a refractive index higher than or equal to 1.50.

14. A prepolymer having thiol end groups obtained from the reaction of a mixture of at least one polythiol and at least one polymerizable compound of formula (I) as defined in claim 1 , wherein the molar ratio of SH / alkyne groups for the mixture of polythiols and polymerizable compounds of formula (I) used for the preparation of said prepolymer is higher than or equal to 7.

15. A process for the preparation of an optical material, comprising the following steps 1), 2), and 3) or 1’), 2’), and 3’):1) Providing a first component comprising at least one prepolymer having thiol end groups obtained by polymerization of a mixture of at least one polythiol and at least one polymerizable compound of formula (I) as defined in any one of claims 1 to 10 in the presence of at least one initiator,2) providing a second component comprising at least one polyisocyanate or polyisothiocyanate,3) Mixing together the first and second components to form a polymerizable composition, and thermally polymerizing said polymerizable composition in the presence of at least one catalyst to obtain the optical material, or:T) Providing a first component comprising at least one prepolymer having isocyanate or isothiocyanate end groups of formula -NCX where X is O or S, obtained by thermal polymerization of a mixture of at least one polyisocyanate or polyisothiocyanate and at least one polymerizable compound of formula (I) as defined in any one of claims 1 to 10 in the presence of at least one catalyst,2’) Providing a second component comprising at least one polythiol,3’) Mixing together the first and second components to form a polymerizable composition, and polymerizing said polymerizable composition in the presence of at least one initiator to obtain the optical material, wherein the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds mixed with said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of SH / alkyne groups present in all said polymerizable compounds is higher than or equal to 7, and the polymerizable composition is obtained from polymerizable compounds such that the polymerizable compounds used to prepare the prepolymer on one hand and the polymerizable compounds mixed with said prepolymer in the polymerizable composition on the other hand are used in amounts adapted so that the molar ratio of NCX / alkyne groups present in all said polymerizable compounds is higher than or equal to 6, X being O or S.

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