Epoxy prepolymer of oligomers containing isosorbide units

Abstract

The present invention relates to an epoxy prepolymer containing isosorbide units, characterized in that it contains less than 1 wt% of isosorbide diglycidyl ether based on the total weight of the epoxy prepolymer. The present invention also relates to a method for producing such an epoxy prepolymer.

Description

[Technical Field]

[0001] This disclosure relates to the field of polyepoxides, and more particularly to epoxy prepolymers containing isosorbide units and methods for preparing the same. More specifically, this disclosure relates to epoxy prepolymers containing isosorbide units that are rich in oligomers and low in monomers and short-chain oligomers. [Background technology]

[0002] Polyepoxides, also known as epoxide polymers or simply "epoxy," are widely used, for example, as surface materials in the manufacture of adhesives or coatings, and also as structural materials, for example, as matrices in composite materials.

[0003] Polyepoxides are obtained by curing a curable composition containing an epoxy prepolymer.

[0004] Within the scope of the present invention, an epoxy prepolymer is a composition comprising a single compound (i.e., a set of identical molecules) containing an epoxide functional group, or a mixture of different compounds containing an epoxide functional group, wherein the compound participates in subsequent polymerization to obtain a polyepoxide.

[0005] The compounds containing epoxide functional groups in the epoxy prepolymer may or may not contain oligomer fractions. They may or may not contain polymer fractions. The epoxy prepolymer can be obtained by mixing the first epoxy prepolymer with a reactive diluent.

[0006] Most curable compositions containing epoxy prepolymers, particularly used in the manufacture of adhesives, coatings, or matrices for composite materials, contain, in addition to the epoxy prepolymer, at least one curing agent and / or at least one accelerator.

[0007] When a curable composition containing an epoxy prepolymer is cured, the ring-opening reaction of the epoxide functional groups of the epoxy prepolymer can form chemical bonds between the compounds contained in the epoxy prepolymer (referred to as "hypopolymerization of the epoxy prepolymer") and / or between the compounds contained in the epoxy prepolymer and the curing agent. This results in the formation of a three-dimensional polymer network.

[0008] The term "accelerator" refers to a compound that can catalyze a homopolymerization reaction between compounds in an epoxy prepolymer, or a reaction between a compound in an epoxy prepolymer and a curing agent. Lewis acids, Lewis bases, and photoinitiators are examples of such compounds.

[0009] The term "curing agent" is understood to mean any compound distinct from the epoxy prepolymer that can react with the epoxide functional groups of the prepolymer to form a three-dimensional network. Examples include amines, amidoamines, Mannich bases, organic acids (including polyesters with terminal carboxylic acid functional groups), organic acid anhydrides, and latent curing agents (such as cyanamides and imidazole types).

[0010] In single-component curable compositions, the accelerator and / or curing agent are directly incorporated into the epoxy prepolymer composition: refer to the 1K system. In two-component curable compositions, the accelerator and / or curing agent are packaged separately from the epoxy prepolymer composition and mixed only when the curable composition is used for molding: refer to the 2K system.

[0011] The curable composition containing the epoxy prepolymer may also contain organic or inorganic fillers (such as silica, sand, aluminum oxide, talc, or calcium carbonate), pigments, plasticizers, stabilizers, and thixotropes.

[0012] Bisphenol A diglycidyl ether (BADGE) of formula (i) is a chemical compound that is currently very widely used as an epoxy prepolymer.

[0013] [Chemical]

[0014] BADGE is a product derived from petroleum, which is disadvantageous in situations of price increases and / or shortages of petroleum resources.

[0015] Furthermore, bisphenol A is currently recognized as an endocrine disruptor.

[0016] Therefore, the handling of epoxy prepolymers based on bisphenol A or contact with polyepoxides obtained from BADGE may be harmful to health.

[0017] In recent years, it has been known that BADGE can be replaced by a mixture containing isosorbide diglycidyl ether (IDGE), a bio-derived product obtained from isosorbide.

[0018] The structure of isosorbide (Formula (ii)) is shown below.

[0019] [Chemical]

[0020] Hereafter, the display of stereochemistry in the isosorbide unit will be omitted.

[0021] The structure of IDGE (Formula (iii)) is shown below.

[0022] [Chemical]

[0023] Today, this compound is widely known and is described in the literature, along with its synthesis method. For example, U.S. Patent No. 3,272,845, U.S. Patent No. 4,770,871, International Publication No. WO 2008 / 147472, International Publication No. WO 2008 / 147473, U.S. Patent No. 3,041,300, International Publication No. WO 2012 / 157832, and International Publication No. WO 2015 / 110758, which disclose the synthesis method of IDGE, can be cited.

[0024] Thus, an entire field of research has emerged for the purpose of enabling the industrial use of IDGE, and more generally, epoxy prepolymers containing isosorbide units.

[0025] However, it has recently been revealed by the applicant that epoxy prepolymers containing isosorbide units developed so far have mutagenicity. As far as the applicant knows, these mutagenic properties were not known elsewhere.

[0026] Continuing that research, the applicant has finally found that it may be possible to reduce or even eliminate their potential mutagenicity by increasing the molar mass of epoxy prepolymers containing isosorbide units. This surprising effect is the basis of the present invention. SUMMARY OF THE INVENTION

[0027] The present disclosure relates to an epoxy prepolymer containing an isosorbide unit, the potential mutagenicity of which is reduced or suppressed.

[0028] Therefore, an epoxy prepolymer containing an isosorbide unit is proposed, which is characterized by containing less than 1% by weight of IDGE based on the total weight of the epoxy prepolymer.

[0029] According to another aspect, a curable composition is proposed, which comprises the epoxy prepolymer composition of the present invention and further contains at least one accelerator and / or at least one curing agent.

[0030] In another embodiment, we propose a polyepoxide obtained by curing the curable composition of the present invention.

[0031] In another embodiment, the present invention proposes a composite material, coating, or adhesive comprising a polyepoxide.

[0032] In another embodiment, the present invention proposes a method for preparing epoxy prepolymers, the method comprising the following steps: - Step a) to provide epoxy prepolymer A containing isosorbide units, -Optionally, steps b) and / or c), where step b) can be performed before step c), or vice versa. -Includes step d) which is performed after any one of steps a), b), or c), Here, step b) includes a step of reacting a polyol with epoxy prepolymer A, or epoxy prepolymer C obtained at the end of step c), or epoxy prepolymer D obtained at the end of step d), in order to obtain epoxy prepolymer B containing isosorbide units with a Mn greater than the Mn of each of epoxy prepolymers A, C, or D. Step c) includes re-functionalizing epoxy prepolymer A, epoxy prepolymer B, or epoxy prepolymer D obtained at the end of step d) in order to obtain epoxy prepolymer C containing isosorbide units having an EEW smaller than the respective EEW of epoxy prepolymers A, B, or D. Step d) includes a step of purifying epoxy prepolymers A, B, or C, which can reduce the isosorbide diglycidyl ether content of epoxy prepolymers A, B, or C.

[0033] In another embodiment, an alternative method for preparing epoxy prepolymers containing isosorbide units is proposed, the method comprising the following steps: e) A step of providing a first epoxy prepolymer that does not contain isosorbide units, f) A reaction step between the first epoxy prepolymer and isosorbide to obtain a second epoxy prepolymer containing isosorbide and containing more Mn units than the first epoxy prepolymer. g) Optionally, the process includes a step of refunctionalizing the second epoxy prepolymer to obtain a third epoxy prepolymer having an EEW smaller than that of the second epoxy prepolymer.

[0034] Further features and advantages of the present invention will be revealed by the following detailed description. [Modes for carrying out the invention]

[0035] In this document, the expression "included in..." should be understood to include the boundary value.

[0036] In this document, the term "glycidyl ether group" refers to a group whose structure is represented by the following formula (iv)

[0037] [ka]

[0038] In this document, the term "isosorbide unit" refers to a group whose structure is represented by the following formula (v).

[0039] [ka]

[0040] In this document, the glycidyl ether group supported on the isosorbide unit has the following structure (formula vi).

[0041] [ka]

[0042] By performing any one of the methods for synthesizing IDGE described in U.S. Patent No. 3,272,845, U.S. Patent No. 4,770,871, International Publication No. 2008 / 147472, International Publication No. 2008 / 147473, U.S. Patent No. 3,041,300, International Publication No. 2012 / 157832, and International Publication No. 2015 / 110758, epoxy prepolymers containing isosorbide monoglycidyl ether (IMGE) can be obtained, as can oligomers containing isosorbide units and glyceryl units.

[0043] In this document, the term "glyceryl unit" refers to a group whose structure is represented by the following formula (vii).

[0044] [ka]

[0045] These oligomers may contain one or more glycidyl ether moieties supported by isosorbide units and / or glyceryl units.

[0046] As an example, the structures of two oligomers sometimes found in epoxy prepolymers containing IDGE are shown below.

[0047] Therefore, the following oligomer is referred to in this document as diglycidyl ether diisosorbide glyceryl (DGEDIG; formula (viii)).

[0048] [ka]

[0049] Furthermore, the following oligomer is referred to in this document as diglycidyl ether triisosorbide diglyceryl (DGETIDG; formula (ix)).

[0050] [ka]

[0051] In this document, the term "alcohol-based epoxy prepolymer" refers to an epoxy prepolymer in which the epoxide functional group is essentially contained in a glycidyl ether group, and at least 5% of the glycidyl ether group is supported on the alcohol unit or a glyceryl unit to which it is itself bonded.

[0052] For example, in isosorbide-based epoxy prepolymers, at least 5% of glycidyl ether groups are supported by isosorbide units and glyceryl units bonded to the isosorbide units. These glycidyl ether groups are present, for example, within the IMGE, within the IDGE, within the glycidyl ether-isosorbide units contained in the oligomer, or within the glycidyl ether-glyceryl-isosorbide units contained in the oligomer.

[0053] An example of a glycidyl ether-glyceryl-isosorbide unit is shown below (formula x).

[0054] [ka]

[0055] The epoxy prepolymer obtained by carrying out the IDGE synthesis method described in the literature cited above is an isosorbide-based epoxy prepolymer.

[0056] The epoxy prepolymer may also be based on several alcohols. For example, an epoxy prepolymer based on alcohol 1 and alcohol 2 is an epoxy prepolymer in which the epoxide functional groups are essentially contained in glycidyl ether groups, at least 5% of the glycidyl ether groups are supported by units of alcohol 1 or by glyceryl units that are themselves bonded to units of alcohol 1, and at least 5% of the glycidyl ether groups are supported by units of alcohol 2 or by glyceryl units that are themselves bonded to units of alcohol 2.

[0057] In this application, the term "alcohol-based polyepoxide" refers to a polyepoxide obtained by curing a curable composition containing an alcohol-based epoxy prepolymer.

[0058] The weight epoxy equivalent (EEW) of an epoxy prepolymer is defined as the mass of the epoxy prepolymer containing 1 mole of glycidyl ether groups. For example, pure IDGE (formula ii) with a molar mass of 258 g / mol and containing 2 glycidyl ether groups has an EEW of 129 g / eq.

[0059] In diol-based epoxy prepolymers, the EEW is minimized when the epoxy prepolymer is a diglycidyl ether of the pure diol. Generally, as the content of oligomers and / or monoglycidyl ethers of the diol in the epoxy prepolymer increases, the EEW of the epoxy prepolymer increases.

[0060] By using epoxy prepolymers with low EEW (Energy-Emitting Weld), polyepoxides with a three-dimensional network and high crosslinking density can be obtained. The high nodal density allows for the production of materials with a higher glass transition temperature (Tg) and greater chemical and mechanical resistance.

[0061] We propose an epoxy prepolymer characterized by containing less than 1% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight, of IDGE relative to the total weight of the epoxy prepolymer.

[0062] Therefore, unlike prior art epoxy prepolymers containing isosorbide units, which have a high IDGE content, the epoxy prepolymer of the present invention has a low IDGE content.

[0063] This can reduce their potential mutagenicity, as demonstrated by the tests described in the "Examples" section of this document.

[0064] According to one embodiment, the epoxy prepolymer according to the present invention comprises less than 1% by weight of IDGE and less than 1% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight of IMGE, relative to the total weight of the epoxy prepolymer.

[0065] For example, the epoxy prepolymer according to the present invention comprises less than 0.5% by weight of IDGE and less than 1% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight of IMGE relative to the total weight of the epoxy prepolymer.

[0066] For example, the epoxy prepolymer according to the present invention comprises less than 0.1% by weight of IDGE relative to the total weight of the epoxy prepolymer, and less than 1% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight of IMGE relative to the total weight of the epoxy prepolymer.

[0067] Preferably, in the epoxy prepolymer of the present invention, a compound containing an isosorbide unit having a molar mass of less than 300 g / mol, preferably less than 500 g / mol, and more preferably less than 800 g / mol, corresponds to less than 1% by weight of the total weight of the prepolymer.

[0068] For example, in the epoxy prepolymer of the present invention, a compound containing an isosorbide unit having a molar mass of less than 300 g / mol, preferably less than 500 g / mol, and more preferably less than 800 g / mol, corresponds to less than 0.5% by weight of the total weight of the prepolymer.

[0069] For example, in the epoxy prepolymer of the present invention, a compound containing an isosorbide unit having a molar mass of less than 300 g / mol, preferably less than 500 g / mol, and more preferably less than 800 g / mol, corresponds to less than 0.1% by weight of the total weight of the prepolymer.

[0070] Compounds other than IDGEs that contain isosorbide units and are commonly found in epoxy prepolymers containing isosorbide units, for example, those with low molar masses of less than 800 g / mol, may also have relatively high potential mutagenicity. Presumably, among these compounds, the closer their structure (and therefore their molar mass) is to that of IDGE, the closer their potential mutagenicity will be to that of IDGE. Conversely, among compounds heavier than IDGE, the higher their molar mass, the lower their potential mutagenicity.

[0071] Among compounds with a molar mass of less than 800 g / mol, some may contain one, two, or three isosorbide units, and their structure may be similar to that of IDGE (which has a molar mass of 258.3 g / mol).

[0072] Among compounds with a molar mass of less than 300 g / mol, some compounds containing one isosorbide unit, such as IMGE, may be found.

[0073] Among compounds with a molar mass of less than 500 g / mol, some contain two isosorbide units, such as DGEDIG, which has a molar mass of 460.5 g / mol.

[0074] Among compounds with a molar mass of less than 800 g / mol, some contain three isosorbide units, such as DGETIDG, which has a molar mass of 662.7 g / mol.

[0075] The absence of IDGE or other compounds with a molar mass of less than 800 g / mol can be confirmed by size exclusion chromatography, with the chromatography column calibrated using polystyrene standards. Therefore, it is sufficient to confirm that the chromatogram does not show a signal corresponding to a molar mass lower than 800 g / mol.

[0076] Using gas-phase chromatography with external standards, compounds containing isosorbide units such as IMGE or IDGE can be analyzed.

[0077] Mass spectroscopy techniques can be used to identify compounds with higher molar masses, particularly oligomers containing two or three isosorbide units, such as DGEDIG or DGETIDG. Specifically, techniques such as MALDI (matrix-assisted laser desorption / ionization), LC-MC (liquid chromatography-mass spectrometry), or ESI MS (electrospray ionization mass spectrometry) can be employed.

[0078] Preferably, the number-average molar mass (Mn) of the compound containing the isosorbide unit in the epoxy prepolymer of the present invention is greater than 1000 g / mol, and preferably 1000 to 8000 g / mol.

[0079] The tests described in the "Examples" section of this document were performed on epoxy prepolymers that essentially contain compounds with isosorbide units. In these tests, if the Mn of the epoxy prepolymer is greater than 1000 g / mol, the epoxy prepolymer is not mutagenic.

[0080] Preferably, the epoxy prepolymer of the present invention has Mn greater than 1000 g / mol, preferably 1000 to 8000 g / mol.

[0081] Mn values ​​below 8000 g / mol correspond to oligomeric compositions, which are easier to handle than polymer compositions.

[0082] Preferably, the Mn referred to in this document corresponds to Mn measured by size exclusion chromatography with a chromatography column calibrated using a polystyrene standard.

[0083] Preferably, the epoxy prepolymer of the present invention has an EEW of less than 1000 g / eq., more preferably 230 to 1000 g / eq., and even more preferably 300 to 600 g / eq.

[0084] Epoxy prepolymers containing very low EEW isosorbide units may be equivalent to epoxy prepolymers with high IDGE content and / or compounds containing low molar mass isosorbide units. In practice, epoxy prepolymers containing less than 230 g / eq. EEW isosorbide units are very likely to have excessively high potential mutagenicity.

[0085] Preferably, the epoxy prepolymer of the present invention contains a glycidyl ether group.

[0086] Preferably, the epoxy prepolymer of the present invention comprises glycidyl ether groups supported by isosorbide units.

[0087] Preferably, the epoxy prepolymer of the present invention contains glyceryl units.

[0088] Glyceryl units are generally present in oligomers that are present in epoxy prepolymers containing isosorbide units.

[0089] Preferably, the epoxy prepolymer of the present invention comprises glycidyl ether groups supported by glyceryl units.

[0090] In oligomers present in epoxy prepolymers containing isosorbide units, glyceryl units typically have free hydroxyl functional groups. To reduce the EEW of the epoxy prepolymer containing the oligomer, these free hydroxyl functional groups can be re-functionalized with epoxidizing groups such as glycidyl ether groups. This yields an epoxy prepolymer containing glycidyl ether groups supported by glyceryl units.

[0091] Preferably, the epoxy prepolymer of the present invention is an isosorbide-based epoxy prepolymer.

[0092] For example, the epoxy prepolymer of the present invention is based on an epoxy prepolymer based on isosorbide, wherein at least 10%, preferably at least 30%, more preferably at least 50%, and even more preferably at least 80% of glycidyl ether groups are supported by isosorbide units or by glyceryl units that are themselves bonded to isosorbide units.

[0093] Preferably, the epoxy prepolymer of the present invention comprises 5 to 85%, more preferably 5 to 75%, and even more preferably 30 to 70% by weight of isosorbide units relative to the total weight of the epoxy prepolymer.

[0094] Therefore, epoxy prepolymers containing high concentrations of bio-derived units exist.

[0095] According to one embodiment, the epoxy prepolymer of the present invention comprises a polyol unit which is different from an isosorbide unit and different from a glyceryl unit, selected, for example, from the following list of non-limiting alcohol units. - Pentaerythritol, - Trimethylolethane, - Trimethylolpropane, -Spiroglycol, -Tricyclodecanedimethyl, -Ethylene glycol, -Propylene glycol, -pentane-1,5-diol, -Hexane-1,6-diol, C such that -x ≥ 7 x Aliphatic diols, -y=2,3 or 4, 1,y-cyclohexanedimethanol, -Fran-i,j-dimethanol with {i,j}={1,4}, {1,3}, or {2,3} Thiophen-i,j-dimethanol with -{i,j}={1,4}, {1,3}, or {2,3}.

[0096] Preferably, the polyol unit distinct from the isosorbide unit is a diol unit, for example, a diol unit selected from the diol units listed above.

[0097] More preferably, the polyol unit distinct from the isosorbide unit is the 1,4-cyclohexanedimethanol unit.

[0098] For example, the epoxy prepolymer of the present invention contains 5 to 80 mol%, preferably 20 to 60 mol%, of different polyol units of isosorbide units, relative to the amount of isosorbide units contained in the epoxy prepolymer, and these polyol units are different from glyceryl units.

[0099] For example, if the epoxy prepolymer of the present invention contains 50 mol% of different polyol units that are different from the isosorbide units and different from the glyceryl units, relative to the amount of isosorbide units contained in the epoxy prepolymer, this means that the epoxy prepolymer contains twice the number of moles of polyol units that are different from the isosorbide units and different from the glyceryl units. The same applies if it is 20% and five times more.

[0100] According to another aspect of the present invention, a curable composition comprising the epoxy prepolymer composition according to the present invention is proposed, characterized by further comprising at least one accelerator and / or at least one curing agent.

[0101] The term "curable composition" is intended to mean a liquid mixture that can polymerize to form a crosslinked (cured) resin. For example, a curable composition containing an epoxy prepolymer is a liquid mixture that can polymerize to form a polyepoxide, which is, by definition, a crosslinked resin.

[0102] The curable composition may, for example, contain a curing agent. Therefore, the {epoxy prepolymer, curing agent} system may be stoichiometric, or it may contain an excess of reactive functional groups or epoxy functional groups of the curing agent.

[0103] According to another aspect of the present invention, a polyepoxide obtained by curing the curable composition of the present invention is proposed.

[0104] The curing (i.e., crosslinking) of the curable composition of the present invention may occur spontaneously or may require heating or irradiation with UV radiation.

[0105] The heating may be, for example, a curing cycle that optionally includes time at room temperature followed by one or more heating times at an increasing temperature between 30°C and 260°C.

[0106] According to another aspect of the present invention, a composite material, coating, or adhesive comprising the polyepoxide of the present invention is proposed.

[0107] The composite material of the present invention may be a {polyepoxide; fiber} type composite material, and the fibers may be selected in particular from glass fibers, carbon fibers, basalt fibers, and plant fibers (flax, hemp).

[0108] The composite material of the present invention may be useful in the manufacture of structurally functional components in fields such as automobiles, ships, aerospace, or even sports and leisure.

[0109] According to another aspect of the present invention, a method for preparing the epoxy prepolymer of the present invention is proposed, the method comprising the following steps, namely, - Step a) to provide epoxy prepolymer A containing isosorbide units, - Any step b) and / or step c), where step b) can be performed before step c), or vice versa. -Includes step d) which is performed after any one of steps a), b), or c),

[0110] Here, step b) includes a reaction step of a polyol with epoxy prepolymer A, or epoxy prepolymer C obtained at the end of step c), or epoxy prepolymer D obtained at the end of step d), in order to obtain epoxy prepolymer B containing isosorbide units with a Mn greater than the Mn of each of epoxy prepolymers A, C, or D.

[0111] Step c) includes re-functionalizing epoxy prepolymer A, epoxy prepolymer B, or epoxy prepolymer D obtained at the end of step d) in order to obtain epoxy prepolymer C containing isosorbide units having an EEW smaller than the respective EEW of epoxy prepolymers A, B, or D.

[0112] Step d) includes a step of purifying epoxy prepolymers A, B, or C, which can reduce the isosorbide diglycidyl ether content of epoxy prepolymers A, B, or C.

[0113] The epoxy prepolymer A in step a) may be provided by synthesis. In that case, it is not limited to a specific synthesis method. It may be any synthesis method of epoxy prepolymers containing isosorbide units known in the prior art, for example, the method described in the literature cited above.

[0114] Epoxy prepolymer A may be more or less rich in oligomers.

[0115] The literature discloses various techniques for forming oligomer-rich oligomers. These techniques have been developed primarily for bisphenol A-based epoxy prepolymers.

[0116] One of these techniques involves reacting a low-molar epoxy prepolymer with a diol, where the reaction between the epoxy groups of the prepolymer and the hydroxyl functional groups of the diol oligomerizes the mixture and increases its molecular weight (fusion process).

[0117] Step b) includes performing the fusion process.

[0118] Another technique, called the Taffy process, involves the direct synthesis of oligomers by reacting a diol with a limited amount of epichlorohydrin or another reagent that can introduce an epoxide functional group.

[0119] In the Taffy process, because the amount of epichlorohydrin is limited, the hydroxyl functional group of the diol can be partially utilized to react in the ring-opening reaction of the epoxide ring already supported by the diol unit, thereby promoting oligomer formation.

[0120] According to certain embodiments, the method for preparing epoxy prepolymers of the present invention can combine a step corresponding to a fusion process with a step corresponding to a toffee process. This corresponds to the case where the method according to the present invention includes both step a) and step b) which carry out the toffee process.

[0121] The method according to the present invention may include step c) re-functionalization of the epoxy prepolymer, which can be obtained to have a relatively low EEW despite the presence of oligomers in the epoxy prepolymer.

[0122] The method according to the present invention includes step d), which is a step of purifying the epoxy prepolymer that can reduce the IDGE content of the epoxy prepolymer.

[0123] Steps b) and c) are optional and one may be performed before the other or vice versa, and step d) may be performed after any one of steps a), b), or c), and the method of the present invention may include any one of the following orders. - Process a), then process d), - Process a), then process b), then process d), - Process a), then process d), then process b), - Process a), then process c), then process d), - Process a), then process d), then process c), - Process a), then process b), then process c), then process d), - Process a), then process b), then process d), then process c), - Process a), then process d), then process b), then process c), - Process a), then process c), then process b), then process d), - Process a), then process c), then process d), then process b), - Process a), then process d), then process c), then process b).

[0124] According to a preferred embodiment of the method of the present invention, the method of the present invention may include any one of the following in order: - Process a), then process d), - Process a), then process b), then process d), - Process a), then process d), then process b), - Process a), then process d), then process c), - Process a), then process b), then process c), then process d), - Process a), then process b), then process d), then process c), - Process a), then process d), then process b), then process c), - Process a), then process d), then process c), then process b).

[0125] According to a more preferred embodiment of the method of the present invention, the method of the present invention may include any one of the following in order: - Process a), then process d), - Process a), then process b), then process d), - Process a), then process d), then process b), - Process a), then process b), then process c), then process d), - Process a), then process b), then process d), then process c), -Step a), then step d), then step b), then step c).

[0126] According to this last embodiment, the method for preparing the epoxy prepolymer of the present invention comprises the following steps, namely: - Step a) to provide epoxy prepolymer A containing isosorbide units, -Optionally, step b), or if the method includes steps b) and c), step b) is performed before steps c), -Includes step d) which is performed after any one of steps a), b), or c), Here, step b) includes a step of reacting a polyol with epoxy prepolymer A or epoxy prepolymer D obtained at the end of step d) to obtain epoxy prepolymer B containing isosorbide units with a Mn greater than the respective Mn of epoxy prepolymer A or D, Step c) includes re-functionalizing epoxy prepolymer B or epoxy prepolymer D obtained at the end of step d) in order to obtain epoxy prepolymer C containing isosorbide units having an EEW smaller than the respective EEW of epoxy prepolymer B or D.

[0127] Step d) includes a purification step of epoxy prepolymers A, B, or C that can reduce the isosorbide diglycidyl ether content of epoxy prepolymers A, B, or C).

[0128] Preferably, step d) is performed as the final step of steps a), b), c), and d). This can increase the efficiency of the method.

[0129] According to one embodiment, in the method of the present invention, step a) is - Isosorbide, - 2 to 3 equivalents of epichlorohydrin relative to the amount of isosorbide, - The reaction step involves adding 2 to 2.5 equivalents of a first basic reagent relative to the amount of isosorbide.

[0130] Preferably, the first basic reagent is selected from lithium hydroxide, potassium hydroxide, calcium hydroxide, or sodium hydroxide, more preferably in the form of an aqueous solution, and even more preferably an aqueous solution of sodium hydroxide.

[0131] According to one embodiment, the reaction step between isosorbide, epichlorohydrin, and a basic reagent in step a) is carried out in the presence of a phase transfer catalyst in an amount of 0.01 to 1% by weight relative to the weight of isosorbide, preferably the phase transfer catalyst is selected from tetraalkylammonium halides, sulfates, or bisulfates, and more preferably the following formula, i.e., X - R4N + A compound having is selected, in the formula X - Cl - , Br - , or I - R is selected from ethyl, propyl, or butyl groups, and more preferably, the phase transfer catalyst is selected from tetraethylammonium bromide, tetrabutylammonium bromide, or tetrabutylammonium iodide.

[0132] For example, the amount of phase transfer catalyst in step a) is 0.01 to 0.2% by weight relative to the weight of isosorbide.

[0133] For example, the amount of phase transfer catalyst in step a) is 0.2 to 0.4% by weight relative to the weight of isosorbide.

[0134] For example, the amount of phase transfer catalyst in step a) is 0.4 to 0.6% by weight relative to the weight of isosorbide.

[0135] For example, the amount of phase transfer catalyst in step a) is 0.6 to 0.8% by weight relative to the weight of isosorbide.

[0136] For example, the amount of phase transfer catalyst in step a) is 0.8 to 1% by weight relative to the weight of isosorbide.

[0137] The addition of a phase-transfer catalyst can limit the formation of oligomers for the same amount of epichlorohydrin. The less phase-transfer catalyst used, the longer and more abundant the oligomers will be on average.

[0138] According to one embodiment, the reaction step between isosorbide, epichlorohydrin and the first basic reagent in step a) is carried out in the absence of a phase transfer catalyst.

[0139] According to one embodiment, step b) of the method of the present invention, the reaction between the polyol and epoxy prepolymer A, C, or D, comprises a reaction between the epoxy prepolymer A, C, or D and the polyol in an inert atmosphere at a temperature of 150°C to 180°C, in the presence of one second basic reagent in an amount between 0.1% to 2% by weight relative to the mass of each epoxy prepolymer A, C, or D, wherein the second basic reagent is selected from lithium hydroxide, potassium hydroxide, calcium hydroxide, or sodium hydroxide, and more preferably sodium hydroxide.

[0140] For example, in this embodiment, the reaction between the polyol and epoxy prepolymers A, C, or D can be carried out in or without the presence of a phase transfer catalyst.

[0141] The addition of a phase-transfer catalyst in step b) accelerates the reaction. The phase-transfer catalyst can also provide better control over oligomer formation.

[0142] According to one embodiment, in the method according to the present invention, the polyol reacted in step b) is a diol, and preferably the diol is one of the following diols, namely, - Isosorbide -Isoizide -Isomannide -Spiroglycol, -Tricyclodecanedimethyl, -Ethylene glycol, -Propylene glycol, -pentane-1,5-diol, -Hexane-1,6-diol, C such that -x ≥ 7 x Aliphatic diols, -y=2,3 or 4, 1,y-cyclohexanedimethanol, -Furan-i,j-dimethanol where {i,j} = {1,4}, {1,3} or {2,3}, -Thiophene-i,j-dimethanol where {i,j} = {1,4}, {1,3} or {2,3}, and -Selected from mixtures thereof,[[]]END]] More preferably, the diol is 1,4-cyclohexanedimethanol or isosorbide.[[]]END]]

[0143] The choice of polyol affects the reaction rate of step b) and also affects the physical and chemical properties of the polyepoxide obtained from the epoxy prepolymer.[[]]END]]

[0144] It can be particularly advantageous to use a polyol that accelerates the reaction rate of step b) in order to limit the hydrolysis of the epoxy functional group and maintain a relatively low EEW.[[]]END]]

[0145] In one embodiment, in the method of the present invention, the re-functionalization step c) is -Epoxy prepolymer A, B or D,[[]]END]] -4 to 6 equivalents of epichlorohydrin relative to the amount of hydroxyl functional groups present in epoxy prepolymer A, B or D, and -Includes the step of reaction between epoxy prepolymer A, B or D and 0.8 to 1.2 equivalents of one third basic reagent relative to the amount of hydroxyl functional groups present in epoxy prepolymer A, B or D.[[]]END]]

[0146] The amount of hydroxyl functional groups in the epoxy prepolymer can be determined, for example, by integrating the signal corresponding to the OH of the alcohol by 1H NMR in DMSO.[[]]END]] 1 H NMR can be used to determine the amount of hydroxyl functional groups in the epoxy prepolymer by integrating the signal corresponding to the OH of the alcohol.[[]]END]]

[0147] Preferably, the third basic reagent is selected from lithium hydroxide, potassium hydroxide, calcium hydroxide or sodium hydroxide, more preferably in the form of an aqueous solution, and even more preferably an aqueous solution of sodium hydroxide.[[]]END]] [[]]END]]

[0148] [[]]END]] [[]]END]]Preferably, in the method of the present invention, the purification step includes a membrane purification step, and preferably, the membrane purification step includes a dialysis step, a nanofiltration step, or an ultrafiltration step.

[0149] Preferably, the membrane purification step is carried out using a membrane (for example, one contained in a dialysis filter or tube) having a cutoff threshold of 1000 g / mol.

[0150] Preferably, step d) comprises dissolving epoxy prepolymer A, B, or C in an organic solvent or aqueous solvent prior to the film purification step, and more preferably, the solution is dissolved in the form of an aqueous solution containing epoxy prepolymer A, B, or C at a concentration of 10% to 50% by weight relative to the total weight of the aqueous solution containing epoxy prepolymer A, B, or C.

[0151] According to another aspect of the present invention, an alternative method for preparing epoxy prepolymers according to the present invention is proposed, the method comprising the following steps: e) A step of providing a first epoxy prepolymer that does not contain isosorbide units, f) A step of reaction between the first epoxy prepolymer and isosorbide to obtain a second epoxy prepolymer containing isosorbide and having more Mn units than the first epoxy prepolymer. g) Optionally, the process includes a step of refunctionalizing the second epoxy prepolymer to obtain a third epoxy prepolymer having an EEW smaller than that of the second epoxy prepolymer.

[0152] This alternative method for preparing epoxy prepolymers according to the present invention ensures that IMGE or IDGE is not formed in any step of the method.

[0153] Step e) can be carried out by synthesis according to any method known to those skilled in the art. The chemical properties of the first epoxy prepolymer, which does not contain isosorbide units, are not particularly limited in any other respect.

[0154] According to one embodiment, step f) of the reaction between isosorbide and the first epoxy prepolymer comprises a reaction between the first epoxy prepolymer and isosorbide in an inert atmosphere at a temperature of 150°C to 180°C, in the presence of a fourth basic reagent in an amount between 0.1% to 2% by weight relative to the mass of the first epoxy prepolymer, wherein the fourth basic reagent is selected from lithium hydroxide, potassium hydroxide, calcium hydroxide, or sodium hydroxide, with sodium hydroxide being more preferred.

[0155] For example, according to this embodiment, the reaction between isosorbide and the first epoxy prepolymer can be carried out in or without the presence of a phase transfer catalyst.

[0156] The addition of the phase transfer catalyst in step f), which corresponds to the Taffy process, accelerates the reaction, limits the hydrolysis of the epoxide functional group, and therefore allows for the maintenance of a relatively low EEW.

[0157] According to one embodiment, the re-functionalization step g) is, - Second epoxy prepolymer, - 4 to 6 equivalents of epichlorohydrin relative to the amount of hydroxyl functional groups present in the second epoxy prepolymer, and -The reaction step involves adding a fifth basic reagent in an amount of 0.8 to 1.2 equivalents relative to the amount of hydroxyl functional groups present in the second epoxy prepolymer.

[0158] The amount of hydroxyl functional groups in epoxy prepolymers is, for example, in DMSO. 1 1H NMR allows us to integrate and determine the signal corresponding to the OH group of an alcohol.

[0159] Preferably, the fifth basic reagent is selected from lithium hydroxide, potassium hydroxide, calcium hydroxide, or sodium hydroxide, and is preferably in the form of an aqueous solution, and more preferably an aqueous solution of sodium hydroxide. [Examples]

[0160] The epoxy equivalent weight (EEW) is measured according to ISO 3001 or ASTM D1652 standards.

[0161] The number-average molar mass (Mn) is measured by size exclusion chromatography, with the chromatography column calibrated using a polystyrene standard.

[0162] The compositions of the mixtures shown in Tables 1 and 4, and the composition of oligomer fraction 1 in Table 6 (see below), were determined by size exclusion chromatography techniques with chromatography columns calibrated using polystyrene standards, as well as by gas chromatography and gravimetric analysis techniques using external standards.

[0163] Example 1: Synthesis of oligomer-rich isosorbide-based epoxy prepolymer by fusion process Step 1: Synthesis of a first isosorbide-based epoxy prepolymer using conventional technology. Isosorbide, epichlorohydrin (5 molar equivalents relative to isosorbide), and tetraethylammonium bromide (TEAB, 1 wt% relative to the mass of isosorbide) are placed in a double-jacketed reactor equipped with a reverse Dean-Stark apparatus. The medium is stirred and heated to 80°C under partial vacuum of 275 mbar. After distilling a sufficient amount of epichlorohydrin to fill the reverse Dean-Stark apparatus, a 50 wt% aqueous sodium hydroxide solution (2.1 molar equivalents relative to the amount of isosorbide) is added dropwise over 3 hours. During the addition of sodium sulfate, the water-epichlorohydrin azeotrope mixture can be distilled and separated in the Dean-Stark apparatus to remove the water introduced and formed during the reaction. After the addition of sodium hydroxide is complete, the medium is stirred at 80°C for 1 hour to completely remove water from the reaction medium. Then heating is stopped and the medium is cooled in air at room temperature. The medium is then removed and the salt formed during the reaction is filtered through sintered glass. Next, the salt cake is washed with epichlorohydrin. The filtrate is collected. Washing epichlorohydrin and residual epichlorohydrin are removed using a rotary evaporator. The results of the analysis performed on the obtained epoxy prepolymer are shown in Table 1. [Table 1]

[0164] Step 2: Oligomerization of the first epoxy prepolymer obtained in Step 1. The purpose of this step is to increase the chain length of the first epoxy prepolymer obtained in step 1. In this way, a second epoxy prepolymer is obtained.

[0165] 200 g of the first epoxy prepolymer is placed in a double-jacket reactor equipped with mechanical stirring. The first epoxy prepolymer is heated to 80°C under an inert nitrogen atmosphere. A specified mass proportion of diol (isosorbide or CHDM) is added under nitrogen. The medium is stirred until a homogeneous medium is obtained. A specified amount of catalyst (sodium hydroxide in the form of a 50 wt% aqueous solution, with or without phase-transfer catalyst TEAB) is added under nitrogen. The medium is then heated at 180°C for a specified time. After the reaction is complete, the medium is allowed to cool to 80°C. The medium is removed from the reactor, and the salt formed by the catalyst is filtered at 80°C. The results of the analysis performed on the obtained epoxy prepolymer are shown in Table 2. [Table 2]

[0166] The percentage is the mass percentage relative to the mass of the first epoxy prepolymer introduced. Step 3: Re-functionalization of the second epoxy prepolymer obtained in Step 2.

[0167] To ensure the reactivity of the second epoxy prepolymer, it may be necessary to substitute the hydroxyl functional groups of the second epoxy prepolymer with glycidyl ether groups, thereby obtaining a third epoxy prepolymer whose exclusive energy working width (EEW) is smaller than that of the second epoxy prepolymer.

[0168] For this purpose, 200 g of the second epoxy prepolymer is redissolved in 5 equivalents of epichlorohydrin relative to the hydroxyl functional groups of the oligomer resin (the amount of hydroxyl functional groups is determined by integrating the signal corresponding to the alcohol OH in 1H NMR in DMSO) in a reactor equipped with a distillation system as in step 1. The medium is heated to 80°C and the pressure is reduced to 275 mbar until the epichlorohydrin boils and distills. Then, 1 equivalent of sodium hydroxide (in the form of a 50 wt% aqueous solution relative to the hydroxyl functional groups) is added over 3 hours using a peristaltic pump. The azeotropic mixture is distilled during the addition and the epichlorohydrin is reintroduced into the reaction medium using a reverse Dean-Stark apparatus. After the addition is complete, distillation of the medium is continued until all water is removed from the reaction medium. Heating is stopped and the reaction medium is cooled in air at room temperature.

[0169] The salt was filtered on sintered glass and washed with 50 mL of epichlorohydrin. The filtrate was collected. The washing epichlorohydrin and residual epichlorohydrin were distilled under reduced pressure using a rotary evaporator. The results of the analysis performed on the obtained epoxy prepolymer are shown in Table 3. [Table 3]

[0170] Table 3 shows the properties of the refunctionalized epoxy prepolymers, and for each refunctionalized epoxy prepolymer prepared, it shows the epoxy prepolymers from which they were prepared.

[0171] Example 2: Synthesis of oligomer-rich isosorbide-based epoxy prepolymer by the Taffy method Isosorbide, epichlorohydrin (3 molar equivalents relative to the amount of isosorbide), and a known amount of TEAB are also placed in a double-jacketed reactor equipped with an inverted Dean-Stark apparatus. The medium is stirred and heated to a temperature of 80°C under partial vacuum of 275 mbar. After the distillation of epichlorohydrin and reflux of the compound through the inverted Dean-Stark apparatus have begun, 2.1 molar equivalents of sodium hydroxide (in 50% aqueous solution) relative to the amount of isosorbide are added dropwise over 3 hours. The water-epichlorohydrin azeotrope mixture is then distilled, and the water thus distilled is removed through the inverted Dean-Stark assembly.

[0172] After the addition of sodium hydroxide is complete, the medium is stirred at 80°C for 1 hour to complete the removal of water from the reaction medium. The medium is then cooled in air at room temperature. The product is then filtered on sintered glass to remove the sodium chloride formed during the reaction. The salt is washed with epichlorohydrin. The filtrate is collected and the epichlorohydrin is distilled using a rotary evaporator.

[0173] Table 4 shows the results of the analysis performed on the obtained epoxy prepolymer. [Table 4]

[0174] The percentages are by mass. The percentages for TEAB are relative to the mass of introduced isosorbide. The percentages for IDGE and oligomers are relative to the total weight of the epoxy prepolymer.

[0175] Example 3: Purification of epoxy prepolymer by film purification To reduce the content of low-molar compounds in the synthesized epoxy prepolymer, membrane purification was performed by dialysis or ultrafiltration.

[0176] dialysis Place 5 g of epoxy prepolymer into a dialysis tube with a cutoff threshold of 1000 g / mol. Seal the tube and place it in a beaker filled with 5 L of demineralized water. Stir the aqueous medium with a magnetic bar at room temperature for 24 hours. During these 24 hours, change the water from the beaker twice.

[0177] After 24 hours of processing, the dialysis tube is retrieved and poured into a flask. The water is evaporated under reduced pressure to obtain an epoxy prepolymer with a reduced content of low molar compounds.

[0178] Ultrafiltration Ultrafiltration is performed using a membrane with a cutoff threshold of 1000 g / mol. Separation is initiated with an aqueous solution containing 20% ​​by weight of epoxy prepolymer.

[0179] Table 5 shows the results of the analysis performed on the obtained epoxy prepolymer. [Table 5]

[0180] Table 5 shows the properties (EEW ​​and Mn) of the epoxy prepolymers obtained after membrane purification, as well as the epoxy prepolymers used and the membrane purification techniques employed for each epoxy prepolymer obtained by membrane purification.

[0181] Example 4: Toxicological evaluation of epoxy prepolymers To determine the potential mutagenicity of epoxy prepolymers, Ames tests were conducted on epoxy resins with different Mn and EEW ratios. The results are expressed as induction levels, i.e., the number of mutant bacterial colonies obtained from a given strain exposed to the compound. An induction ratio of 2 or less indicates that the resin is considered nontoxic. The results are as follows. The results of the Ames tests are shown in Table 6. [Table 6] *The IDGE1 fraction was obtained by wiped film distillation of resin I1 obtained in step 1 of Example 1, and consists of 98% IDGE. ** Oligomer fraction 1 corresponds to the distillation residue of resin I1 produced to obtain fraction IDGE1. It consists of 1.2% IDGE, 40% DGEDIG and glycidyl ether derivatives of DGEDIG, and 35% DGETIDG and glycidyl ether derivatives of DGETIDG. Therefore, it contains essentially short oligomeric chains.

[0182] Increasing the chain length can reduce the potential mutagenicity of epoxy prepolymers containing isosorbide units, and this mutagenicity can even be removed by treating the epoxy prepolymer with a membrane purification process such as dialysis or ultrafiltration.

[0183] Compounds with Mn levels exceeding 1000 g / mol are considered non-mutagenic. Furthermore, since EEW does not affect the potential mutagenicity of epoxy prepolymers beyond the 1000 g / mol Mn threshold, highly functionalized epoxy oligomers can be used safely.

Claims

1. An epoxy prepolymer containing an isosorbide unit, comprising less than 1% by weight of isosorbide diglycidyl ether relative to the total weight of the epoxy prepolymer, An epoxy prepolymer characterized in that the number-average molar mass of the epoxy prepolymer is greater than 1000 g / mol.

2. The epoxy prepolymer according to claim 1, comprising less than 0.5% by weight of isosorbide diglycidyl ether based on the total weight of the epoxy prepolymer.

3. The epoxy prepolymer according to claim 1, comprising less than 0.1% by weight of isosorbide diglycidyl ether based on the total weight of the epoxy prepolymer.

4. The epoxy prepolymer according to any one of claims 1 to 3, wherein the compound containing isosorbide units having a molar mass of less than 800 g / mol is less than 1% by weight of the total weight of the epoxy prepolymer.

5. The epoxy prepolymer according to claim 4, wherein the compound containing the isosorbide unit has a molar mass of less than 500 g / mol.

6. The epoxy prepolymer according to claim 4, wherein the compound containing the isosorbide unit has a molar mass of less than 300 g / mol.

7. The epoxy prepolymer according to any one of claims 4 to 6, wherein the compound containing the isosorbide unit is less than 0.5% by weight relative to the total weight of the epoxy prepolymer.

8. The epoxy according to any one of claims 4 to 7, wherein the compound containing the isosorbide unit is less than 0.1% by weight relative to the total weight of the epoxy prepolymer. Prepolymer.

9. The epoxy prepolymer according to claim 1, wherein the number-average molar mass of the compound containing isosorbide units contained in the epoxy prepolymer is greater than 1000 g / mol.

10. The epoxy prepolymer according to claim 9, wherein the number average molar mass of the compound containing the isosorbide unit contained in the epoxy prepolymer is greater than 1,000 g / mol and less than or equal to 8,000 g / mol.

11. The epoxy prepolymer according to any one of claims 1 to 10, characterized in that the number average molar mass of the epoxy prepolymer is greater than 1,000 g / mol and less than or equal to 8,000 g / mol.

12. The epoxy prepolymer according to any one of claims 1 to 11, characterized in that the EEW of the epoxy prepolymer is less than 1000 g / eq.

13. The epoxy prepolymer according to claim 12, wherein the EEW of the epoxy prepolymer is 230 or more and less than 1000 g / eq.

14. The epoxy prepolymer according to claim 12, wherein the EEW of the epoxy prepolymer is 300 to 600 g / eq.

15. An epoxy prepolymer according to any one of claims 1 to 14, comprising a glycidyl ether group.

16. The epoxy prepolymer according to claim 15, comprising a glycidyl ether group supported by an isosorbide unit.

17. The epoxy prepolymer according to claim 15 or 16, wherein at least 5% of the glycidyl ether groups are supported by isosorbide units or by glyceryl units that are themselves bonded to isosorbide units.

18. The epoxy prepolymer according to claim 17, wherein at least 10% of the glycidyl ether groups are supported by isosorbide units or by glyceryl units that are themselves bonded to isosorbide units.

19. The epoxy prepolymer according to claim 17, wherein at least 30% of the glycidyl ether groups are supported by isosorbide units or by glyceryl units that are themselves bonded to isosorbide units.

20. The epoxy prepolymer according to claim 17, wherein at least 50% of the glycidyl ether groups are supported by isosorbide units or by glyceryl units that are themselves bonded to isosorbide units.

21. The epoxy prepolymer according to any one of claims 1 to 20, comprising 5 to 85% by weight of isosorbide units based on the total weight of the epoxy prepolymer.

22. The epoxy prepolymer according to claim 21, comprising 5 to 75% by weight of isosorbide units based on the total weight of the epoxy prepolymer.

23. The epoxy prepolymer according to claim 21, comprising 30 to 70% by weight of isosorbide units based on the total weight of the epoxy prepolymer.

24. A curable composition comprising the epoxy prepolymer according to any one of claims 1 to 23, further comprising a curing agent and / or accelerator.

25. A polyepoxide obtained by curing the curable composition described in claim 24.

26. A composite material, coating, or adhesive comprising the polyepoxide described in claim 25.

27. A method for preparing an epoxy prepolymer according to any one of claims 1 to 23, comprising the following steps, namely: - Step a) to provide epoxy prepolymer A containing isosorbide units. - Any step b) and / or step c) such that step b) can be performed before step c), or vice versa. - Includes step d) which is performed after any one of steps a), b), or c), Here, step b) includes a step of reacting a polyol with epoxy prepolymer A, or epoxy prepolymer C obtained at the end of step c), or epoxy prepolymer D obtained at the end of step d), in order to obtain epoxy prepolymer B containing isosorbide units with a Mn greater than the Mn of each of epoxy prepolymers A, C, or D. Step c) includes a step of re-functionalizing epoxy prepolymer A or epoxy prepolymer B or epoxy prepolymer D obtained at the end of step d) in order to obtain epoxy prepolymer C containing isosorbide units having an EEW smaller than the respective EEW of epoxy prepolymers A, B or D. A method comprising step d) a purification step of epoxy prepolymer A, B, or C that can reduce the isosorbide diglycidyl ether content of epoxy prepolymer A, B, or C.

28. The method according to claim 27, wherein the purification step includes a membrane purification step.

29. The method according to claim 28, wherein the membrane purification step includes a dialysis step, a nanofiltration step, or an ultrafiltration step.

30. A method for preparing an epoxy prepolymer according to any one of claims 1 to 23, comprising the following steps, namely: e) A step of providing a first epoxy prepolymer that does not contain isosorbide units, f) A step of reacting the first epoxy prepolymer with isosorbide to obtain a second epoxy prepolymer that contains isosorbide and has more Mn units than the first epoxy prepolymer, g) A method comprising optionally a step of refunctionalizing the second epoxy prepolymer to obtain a third epoxy prepolymer having an EEW smaller than that of the second epoxy prepolymer.

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