The present invention relates to a modified epoxy resin and a curable resin composition comprising the same.

Electronic devices, such as organic light emitting diode (OLED) devices, are typically sensitive to moisture and oxygen. In order to protect the devices and prolong their life time, a sealant is usually applied to the frame of the devices as a barrier.

One approach to extend the life time of electronic devices is to employ a glass frit as the sealing material between glass substrates of an assembly comprising an electronic device to produce a hermetic package. Glass frit needs high processing temperatures and lacks flexibility, making it unsuitable for flexible devices. Glass frit also normally requires the use of an organic sealant. Glass flake-loaded organic sealants or glass rods, through softening, have been used as sealant materials with high barrier property, but they also lack flexibility. Conventional epoxy-based sealant materials provide flexibility, but do not have sufficient barrier property and may also suffer from incomplete curing.

Attempts to improve barrier properties of epoxy-based sealant materials include introducing mesogenic moieties into epoxy resins, for example, diglycidyl ether of 4, 4’-dihydroxy-α-methylstilbene (EDHAMS) . However, the barrier property of EDHAMS-containing materials is still unsatisfactory, particularly for electronic devices.

Therefore, there exists a need for a modified thermosetting epoxy resin suitable for sealing electronic devices which provides improved barrier properties.

The present invention provides a novel modified epoxy resin and a curable resin composition comprising the modified epoxy resin. The curable resin composition upon curing has improved barrier properties as compared to EDHAMS upon curing. The curable resin composition of the present invention is suitable as adhesives, sealants and/or encapsulants for electronic devices.

In a first aspect, the present invention is a modified epoxy resin having the structure of formula (I) :

wherein Structure B is an aromatic mesogenic moiety, n is an integer of from 1 to 100, and Structure A has the following structure:

wherein m is 1 or 2； and each R¹ is independently hydrogen, a hydrocarbyl group having from 1 to 12 carbon atoms, a hydrocarbyloxy group having from 1 to 12 carbon atoms, a halogen, -NO₂, -CN, or combinations thereof.

In a second aspect, the present invention is a process of preparing the modified epoxy resin of the first aspect. The process comprises:

reacting a raw material epoxy compound and a difunctional hydroxyl-containing compound comprising an aromatic mesogenic moiety in the presence of a catalyst, wherein the molar ratio of the raw material epoxy compound and the difunctional hydroxyl-containing compound is in a range from 100: 99 to 100: 10； and

wherein the raw material epoxy compound has the structure of

wherein m is 1 or 2； and each R¹ is independently hydrogen, a hydrocarbyl group having from 1 to 12 carbon atoms, a hydrocarbyloxy group having from 1 to 12 carbon atoms, a halogen, -NO₂, -CN, or combinations thereof.

In a third aspect, the present invention is a curable resin composition comprising:

(a) the modified epoxy resin of the first aspect, and (b) a hardener.

In a fourth aspect, the present invention is an electronic device comprising at least one layer obtained by curing the resin composition of the third aspect.

The modified epoxy resin of the present invention has the structure of formula (I) :

wherein Structure B is an aromatic mesogenic moiety, n is an integer of from 1 to 100, and Structure A has the following structure:

wherein m is 1 or 2； and each R¹ is independently hydrogen, a hydrocarbyl group having from 1 to 12 carbon atoms, a hydrocarbyloxy group having from 1 to 12 carbon atoms, a halogen, -NO₂, -CN, or combinations thereof.

“Hydrocarbyl group” in the present invention has the structure of – (CH₂) _ZCH₃, wherein Z＝0-12. Examples of hydrocarbyl groups include -CH₃, -CH₂CH₃, and -CH₂CH₂CH₃.

“Hydrocarbyloxy group” in the present invention has the structure of -O (CH₂) _ZCH₃, wherein Z＝0-12. Examples of hydrocarbyloxy groups include -OCH₃, -OCH₂CH₃, -OCH₂CH₂CH₃.

In formula (I) , each R¹ can be the same or different. Each R¹ may be independently a hydrocarbyl or hydrocarbyloxy group having from 1 to 6 or from 1 to 4 carbon atoms. Each R¹ can also be independently a halogen selected from chlorine or bromine. Preferably, each R¹ is independently selected from hydrogen, chlorine, or -CH₃. More preferably, each R¹ is hydrogen.

In formula (I) , n can be an integer of 1 or more, 5 or more, 10 or more, 15 or more, or even 20 or more, and at the same time, 100 or less, 90 or less, 70 or less, 60 or less, 50 or less, 40 or less, or even 30 or less.

Structure A in formula (I) is preferably selected from the following structure:

Structure B in formula (I) can be an aromatic mesogenic moiety. “Aromatic mesogenic moiety” refers to an aromatic structure moiety which can prompt molecules to form liquid crystal state. Aromatic mesogenic moiety is usually a rigid chain comprising a bridged bond (-X-) in the center of the aromatic mesogenic moiety, where both side of the bridged bond connect with benzene rings to form a conjugate system. The aromatic mesogenic moiety useful in the present invention may have the structure of formula (B) :

wherein p is an integer of from 0 to 3； each R² is independently selected from hydrogen, a hydrocarbyl group having from 1 to 12 carbon atoms, a hydrocarbyloxy group having from 1 to 12 carbon atoms, a halogen, -NO₂, -CN or combinations thereof； and X is selected from -CR₁＝CR₁-, -CR₁＝CR₁-CR₁＝CR₁-, -CR₁＝N-N＝CR₁-, -CR₁＝N-, -N＝N-, -CR₁＝CR₁-CO-O-CH₂-, -CR₁＝CR₁-CO-O-CH₂-CH₂-, -CH₂-O-CO-CR₁＝CR₁-, -CH₂-CH₂-O-CO-CR₁＝CR₁-, -CR₁＝CR₁＝CO-O-, -O-COCR₁＝CR₁-, -CO-NH-, -NH-CO-, -CO-NH-NH-CO-, -C＝C-, -C＝C-C＝C-, -CO-S-, -S-CO-, or combinations thereof； wherein each R₁ is independently selected from H, -CH₃, -CH₂CH₃, -CN, or combinations thereof, and preferred R₁ is H. Preferably, each R² is H.

Structure B is preferably selected from one of the structure of formulae (B1) through (B7) :

or combinations thereof.

More preferred Structure B has the structure of formula (B1) or (B3) .

The modified epoxy resin of the present invention may be selected from one or more of the following structure (1) through (10) , wherein n is as defined in formula (I) above:

The modified epoxy resin of the present invention may have a weight average molecular weight of from 500 or more, or even 1,000 or more, and at the same time, 15,000 or less, 10,000 or less, or even 8,000 or less. The weight average molecular weight may be determined by gel permeation chromatography (GPC) using a polystyrene standard.

The process of preparing the modified epoxy resin of the present invention comprises: reacting a raw material epoxy compound with a difunctional hydroxyl-containing compound comprising an aromatic mesogenic moiety. The raw material epoxy compound useful for preparing the modified epoxy resin has the structure of formula (C) :

wherein m and each R¹ are as defined in formula (I) above.

The difunctional hydroxyl-containing compound useful for preparing the modified epoxy resin comprises one or more aromatic mesogenic moieties which can be the same or different. The difunctional hydroxyl-containing compound may have the following structure:

wherein each R², X and p are as defined in formula (B) above.

The difunctional hydroxyl-containing compound useful for preparing the modified epoxy resin may be selected from the following compounds:

or mixtures thereof.

Preferably, the difunctional hydroxyl-containing compound useful for preparing the modified epoxy resin is 4, 4’-dihydroxy-α-methylsilbene.

In preparing the modified epoxy resin of the present invention, the molar ratio of the raw material epoxy compound having the structure of formula (C) and the difunctional hydroxyl-containing compound may be in a range from 100: 99 to 100: 10, from 27: 26 to 27:20, or from 27: 26 to 27: 25. In the process of preparing the modified epoxy resin, reaction of the raw material epoxy compound and the difunctional hydroxyl-containing compound may be conducted in the presence of one or more catalysts. Examples of suitable catalysts in preparing the modified epoxy resin include tris (dimethylaminomethyl) phenol, tetrabutylammonium bromide, ethyltriphenyl phosphonium acetate, or mixtures thereof. Preferred catalyst is ethyltriphenyl phosphonium acetate. The reaction time may be from 1 to 10 hours or from 2 to 6 hours. The reaction may be conducted at temperature ranging from 110℃ to 150℃ or from 120℃ to 140℃.

The modified epoxy resin of the present invention may be used in various applications including, for example, coatings, adhesives, electrical laminates, structural laminates, structural composites, moldings, castings, and encapsulations.

The curable resin composition of the present invention comprises (a) one or more modified epoxy resins described above, and (b) one or more hardeners.

The hardeners useful in the present invention may include, for example, primary and secondary polyamines, carboxylic acids and anhydrides thereof, aromatic hydroxyl containing compounds, imidazoles, guanidines, urea-aldehyde resins, melamine-aldehydes resins, alkoxylated urea-aldehyde resins, alkoxylated melamine-aldehyde resins, aliphatic amines, cycloaliphatic amines, aromatic amines, and combinations thereof. Particularly suitable hardeners include, for example, methylene dianiline, dicyandiamide, ethylene diamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, urea- formaldehyde resins, melamine-formaldehyde resins, methylolated urea-formaldehyde resins, methylolated melamine-formaldehyde resins, phenol-formaldehyde novolac resins, cresol-formaldehyde novolac resins, sulpfanilamide, diaminodiphenylsulpfone, diethyltoluenediamine, t-butyltoluenediamine, bis-4-aminocyclohexylmethane, isophoronediamine, diaminocyclohexane, hexamethylenediamine, piperazine, aminoethylpiperazine, 2, 5-dimethyl-2, 5-hexanediamine, 1, 12-dodecanediamine, tris-3-aminopropylamine, and combinations thereof. Preferred hardener is sulpfanilamide (also known as 4-aminobenzenesulpfonamide) .

The hardeners are employed in an amount, which will effectively cure the modified epoxy resin. Generally, the hardeners may be used in an amount, for example, from 0.95: 1 to 1.2: 1, or from 1: 1 to 1.05: 1, equivalents of hardener per equivalent of the modified epoxy resin.

The curable resin composition of the present invention may further comprise other additives such as solvents or diluents, fillers such as clay, pigments, dyes, flow modifiers, thickeners, reinforcing agents, mold release agents, wetting agents, stabilizers, fire retardant agents, surfactants, and combinations thereof.

Examples of pigments and/or dyes useful in the curable resin composition comprises copper (II) 2, 9, 16, 23-tetra-ter-butyl-29, copper (II) 2, 3, 9, 10, 16, 17, 23, 24-octakis (octyloxy) -29H, 31H-phthalocyanine, nickel (II) 1, 4, 8, 11, 15, 18, 22, 25-octabutoxy-29H, 31H-phthalocyanine, Zinc 2, 9, 16, 23-tetra-tert-butyl-29H, 31H-phthalocyanine, cobalt (II) phthalocyanine, copper (II) tetrakis (4-cumylphenoxy) phthalocyanine, zinc phthalocyanine, copper phthalocyanine, or mixtures thereof. The pigments and/or dyes may be added in quantities to provide the curable resin composition with the desired color. For example, the pigments and/or dyes may be present in an amount of from 0 to 50 weight percent (wt％) , from 0.5 wt％ to 40 wt％, or from 1 wt％ to 30 wt％, based on the total weight of the curable resin composition.

Examples of suitable solvents or diluents useful in the curable epoxy resin composition include hydrocarbons, ketones, glycol ethers, aliphatic ethers, cyclic ethers, esters, amides, and combinations thereof. Particularly suitable solvents or diluents include, for example, toluene, benzene, xylene, methyl ethyl ketone, methyl isobutyl ketone, diethylene glycol methyl ether, dipropylene glycol methyl ether, dimethylfonnamide, N- methylpyrrolidinone, tetrahydrofuran, propylene glycol methyl ether, and combinations thereof. The solvents or diluents may be present in an amount of from 0 to 99 wt％, from 50 wt％ to 99 wt％, or from 80 wt％ to 99 wt％, based on the total weight of the curable resin composition.

Thickeners, flow modifiers and the like useful in the curable resin composition may be present in an amount of from 0 to 10 wt％, from 0.5 wt％ to 6 wt％, or from 0.5 wt％ to 4 wt％, based on the total weight of the curable resin composition.

Suitable reinforcing materials useful in the curable resin composition may include natural and synthetic fibers in the form of woven fabric, mats, monofilament, multifilament, unidirectional fibers, rovings, random fibers or filaments, inorganic fillers or whiskers, hollow spheres, and the like. Examples of reinforcing materials include, glass, ceramics, nylon, rayon, cotton, aramid, graphite, polyalkylene terephthalates, polyethylene, polypropylene, polyesters, and combinations thereof. The reinforcing materials may be present in an amount of from 0 to 80 wt％, from 0.1 wt％ to 50 wt％, or from 1 wt％ to 50 wt％, based on the total weight of the curable resin composition.

Suitable fillers useful in the curable resin composition may include, for example, inorganic oxides, ceramic microspheres, plastic microspheres, glass microspheres, inorganic whiskers, CaCO₃, and combinations thereof. The fillers can be employed in an amount from 0 to 95 wt％, from 10 wt％ to 80 wt％, or from 40 wt％ to 60 wt％, based on the total weight of the curable resin composition.

Preferably, the curable resin composition of the present invention also comprises nanoparticles of organic clay. The organic clay may include, for example, organic quaternary ammonium salt modified clay, trimethylstearyl ammonium chloride modified clay, dimethyl distearyl ammonium chloride modified clay, methyl tristeary ammonium chloride modified clay, or mixtures thereof. The nanoparticles of organic clay may have a layered structure. The average particle size of the nanoparticles of organic clay may be in a range of 1 nanometer (nm) to 5,000 nm, and preferably in the range of 50 nm to 500 nm. The amount of the nanoparticles of organic clay in the curable resin composition of the present invention may be 0 or more, 0.1 wt％ or more, 0.5 wt％ or more, or even 1 wt％ or more, and at the same time, 50 wt％ or less, 45 wt ％ or less, 40 wt％ or less, or even 35 wt％ or less, based on the weight of the modified epoxy resin.

The curable resin composition of the present invention may be in the form of an adhesive film, a barrier film, a sealant, or an encapsulant for an electronic device. More preferably, the curable resin composition of the present invention is in the form of a sealant for an electronic device. Curing of the curable epoxy resin composition of the present invention may be carried out from room temperature (23±2℃) up to 250℃, for predetermined periods of time which may be from minutes up to hours. The curing conditions may be dependent on the various components used in the curable resin composition such as the hardener used in the composition. Generally, the time for curing or partially curing the epoxy resin composition may be from 2 minutes to 24 days, from 0.5 hour to 7 days, or from one hour to 24 hours. The curing reaction conditions include, for example, carrying out the curing reaction under a temperature, generally in the range of from 60℃ to 250℃, from 50℃ to 230℃, or from 100℃ to 200℃.

The present invention also provides an electronic device comprising at least one layer obtained by curing the curable resin composition of the present invention. The electronic device may be flexible. Flexible electronic devices refer to bendable, rollable and foldable electronic devices, which can be bent without being damaged.

The present invention also provides an electronic device comprising at least two inorganic or hybrid substrates hermetically sealed by the curable resin composition. Examples of suitable inorganic or hybrid substrates, which can be employed in the present invention, include inorganic substrates such as glass and indium tin oxide (ITO) glass； organic substrates such as polyethylene terephthalate (PET) , polyethylene naphthalate (PEN) , and polyimide (PI) ； a multilayer of the inorganic/organic substrates. Preferred substrate is ITO glass； the inorganic substrate coated with PET, PEN or PI； a multilayer comprising one or more layers of the inorganic substrate and one or more layers of the organic substrate. Preferably, the electronic devices are flexible.

Preferred examples of the electronic devices in which the curable resin composition of the present invention may be employed include organic light emitting diode (OLED) devices such as OLED display televisions and phones and LCD televisions and phones.

The curable resin composition of the present invention is particularly suitable as a sealant for OLED devices to protect the organic light emitting layer and/or electrodes in the OLED from oxygen and/or water. The curable resin composition provides electronic devices with lower water vapor transmission rate (WVTR) , thus longer life, as compared to EDHAMS.

Some embodiments of the invention will now be described in the following Examples, wherein all parts and percentages are by weight unless otherwise specified. The following materials are used in the examples:

The following standard analytical equipment and methods are used in the Examples. Water vapor transmission rate (WVTR)

The WVTR values of barrier films are measured at 25℃ and 90％ relative humidity (RH) , or at 38℃ and 100％RH, respectively, following ASTM method F-1249, and using a MOCON PERMATRAN-W 3/33 instrument (MOCON Inc., Minnesota, USA) . The calibration of the instrument for WVTR measurements is performed using polyester standard films provided by MOCON Inc. The RH sensors are calibrated using saturated salt solutions. During testing, water vapor that permeated through the film sample is carried by dry nitrogen gas to an infrared detector. Duplicate samples are used for each measurement.

When a polyimide (PI) film (Kapton HN film manufactured by DuPont) is used as a substrate, a curable resin composition is applied to the PI film, then cured to form a coating layer on the PI film, that is, a bilayer structure. In the WVTR measurement, the permeability of bare PI film (WVTR_{PI film}) is measured, then that of the bilayer (WVTR_Bilayer) is measured. Through the following equation, the permeation rate for the coating layer itself (WVTR_{coating layer}) is calculated.

[Math. 0001]

Molecular weight measurement of polymers is carried out in tetrahydrofuran (THF) (flow rate: 1 mL/min) at 40℃ with Agilent 1200 equipped with a Agilent Refractive Index detector and Two Mixed E columns (7.8mm x 300mm) in tandem. PL Polystyrene (PS) Narrow standards (Part No. : 2010-0101) with molecular weights ranging from 19,760 to 580 g/mol, polynom 3 fitness are used for calibration.

Synthesis of 1, 5-Diglycidoxy naphthalene

A mixture of 1, 5-dihydroxy naphthalene (49.25g) , benzyltrimethylammonium bromide (2.09g) and epichlorohydrin (481ml) was placed in a three-neck flask and refluxed for 40 minutes (min) . NaOH (24.6g) was dissolved in 139ml of water to prepare 15％ NaOH aqueous solution. Then the solution was added into the flask dropwise over a period of 3 hours under reflux. The reaction was carried out for an additional hour at room temperature. The excess epichlorohydrin was removed by vacuum distillation and the final product was washed with water and methanol. A white powder was obtained by recrystallization from isopropyl alcohol and chloroform.

A mixture of 2, 2’-Dihydroxy-1, 1’-binaphthalene (88.04g) ,benzyltrimethylammonium bromide (2.09g) and epichlorohydrin (481ml) was placed in a three-neck flask and refluxed for 40 min. NaOH (24.6g) was dissolved in 139ml of water to prepare 15％ NaOH aqueous solution. Then the solution was added into the flask dropwise over a period of 3 hours under reflux. The reaction was carried out for an additional hour at room temperature. The excess epichlorohydrin was removed by vacuum distillation and the final product was washed with water and methanol. A white powder was obtained by recrystallization from isopropyl alcohol and chloroform.

7.35g 1, 5-Diglycidoxy naphthalene (M_w: 272.30； 27 mmol) , [1, 1′-biphenyl] -4, 4′-diol (BPD) (4.65g, 25 mmol) , and cyclohexanone (50.0g, 53 mL) were added to a flask and heated with stirring under a nitrogen atmosphere to provide a 90℃ solution. Once the 90 ℃ reaction temperature was reached, ethyltriphenylphosphonium acetate. acetic acid complex (70％ solids in methanol) (0.03g, 0.20 wt％ of the diphenol and diglycidylether reactants used) was added to the reactor and heating continued to 130℃. After 6 hours at 130℃, the reaction product was cooled to room temperature and poured into a mixture of 1: 1 methanol-water to precipitate a white solid. The reaction diagram of preparing the copolymer of naphenyl epoxy and biphenyl diol ( “Polymer 1” ) is shown below:

The obtained Polymer 1 had the following properties: PS equivalent number average molecular weight (M_n) ＝2,120 g/mol, PS equivalent weight average molecular weight (M_w) ＝4,603 g/mol, and polydispersity index (PDI) ＝2.17. In addition, GPC curve of Polymer 1 showed many peaks in the range of low molar mass, which indicates that Polymer 1 also contained small amounts of monomers, dimers, and trimers.

11.25g 2, 2′-Diglycidoxy-1, 1′-binaphthalene (M_w: 389.6； epoxide equivalent weight (EEW) ＝215g/eq, 27 mmol) , [1, 1′-biphenyl] -4, 4′-diol (BPD) (4.65g, 25 mmol) , and cyclohexanone (50.0g, 53 mL) were added to a flask and heated with stirring under a nitrogen atmosphere to provide a 90℃ solution. Once the 90℃ reaction temperature was reached, ethyltriphenylphosphonium acetate. acetic acid complex (70％ solids in methanol) (0.03g, 0.20 wt％ of the diphenol and diglycidylether reactants used) was added to the reactor and heating continued to 130℃. After 6 hours at 130℃, the reaction product was cooled to room temperature and poured into a mixture of 1: 1 methanol-water to precipitate a white solid. The reaction diagram of preparing the copolymer of bi-naphenyl epoxy and biphenyl diol is shown below.

The obtained Polymer 2 had the following properties: PS equivalent M_n＝1,867 g/mol, PS equivalent M_w＝3,069 g/mol, and PDI＝1.64. In addition, GPC curve of Polymer 2 showed many peaks in the range of low molar mass, which indicates that Polymer 2 also contained small amounts of monomers, dimers, and trimers.

Curable epoxy resin composition of Comp Ex A was prepared based on formulations listed in Table 1. A release agent (Yinjing LR-13, U.S. YINJING International (H. K) Co. Ltd. ) was coated on a glass plate (100 mm by 150 mm) . Copper tape with a thickness of 50 μm was bonded on the glass plate for controlling the thickness of the film. EDHAMS and sulphanilamide (SAA) were melted at 150℃, respectively, and then were mixed together at this temperature. The obtained mixture was poured onto the surface of heated glass plate (the surface temperature being about 150 ℃) immediately. Another glass plate was covered slowly to avoid any air bubbles and press the plates slightly. The sample plates were then cured for 2 hours at 100℃, 2 hours at 150℃ and finally 2 hours at 180℃ in an oven (Shanghai Jing Hong Lab Equipment Co., Ltd. ) . WVTR properties of the cured samples were evaluated according to the test method described above and results are listed in Table 2.

Curable epoxy resin composition of Comp Ex B was prepared based on formulations listed in Table 1. A release agent was coated on a glass plate (100 mm by 150 mm) . Copper tape with a thickness of 50 μm was bonded on the glass plate for controlling the thickness of the film. EDHAMS was melted at 150℃. 2 wt％ of nanoparticles of organic clay (NANOCOR I. 30P) was added and stirred for 1 hour. Then, SAA was melted at 150℃ and mixed with the mixture of EDHAMS and organic clay nanoparticles at this temperature. The mixture was poured onto the surface of heated glass plate (the surface temperature being about 150℃) immediately. Another glass plate was covered slowly to avoid any air bubbles and press the plates slightly. The sample plates were then cured for 2 hours at 100℃, 2 hours at 150℃ and finally 2 hours at 180℃ in an oven. WVTR properties of the cured samples were evaluated according to the test method described above and results are listed in Table 2.

Curable epoxy resin composition of Ex 3 was prepared based on formulations listed in Table 1.20 wt％ Polymer 1 was dissolved into N-methylpyrrolidone (NMP) by mechanical stirring for 30 min. Then 8 wt％ SAA was added into the obtained solution and stirred for 10 min. Afterwards, the solution was coated on a PI film with a thickness of 5 mil (127 μm) by blade coating. The gap between blade and PI film was 100 μm. After coating, the samples were cured for 1 hour at 150℃ in an oven. WVTR properties of the cured samples were evaluated according to the test method described above and results are listed in Table 2.

Curable epoxy resin composition of Ex 4 was prepared based on formulations listed in Table 1.20 wt％ Polymer 2 was dissolved into NMP by mechanical stirring for 30 min. Then 33 wt％ of nanoparticles of organic clay (NANOCOR I. 30P) was added and stirred for 1 hour. 8 wt％ SAA was added into the obtained solution and stirred for 10 min. Afterwards, the solution was coated on a PI film with a thickness of 5 mil (127 μm) by blade coating. The gap between blade and the PI film was 100 μm. After coating, the samples were cured for 1 hour at 150℃ in an oven. WVTR properties of the cured samples were evaluated according to the test method described above and results are listed in Table 2.

Curable epoxy resin composition of Ex 5 was prepared based on formulations listed in Table 1.20 wt％ Polymer 1 was dissolved into N-methylpyrrolidone (NMP) by mechanical stirring for 30 min. Then 8 wt％ SAA was added into the solution and stirred for 10 min. Afterwards, the solution was coated on a PI film with a thickness of 5 mil (127 μm) by blade coating. The gap between blade and the PI film was 100 μm. After coating, the samples were cured for 1 hour at 150℃ in an oven, followed by heating the oven to 300℃ and maintaining for 40 min. WVTR properties of the cured samples were evaluated according to the test method described above and results are listed in Table 2.

*Wt％ herein is based on the total weight of the curable epoxy resin composition.

As shown in Table 2, as compared to EDHAMS, Polymer 1 and Polymer 2 of the present invention both provided cured samples with better moisture barrier performance even after heating at 300℃ for 40 min.