Thermally stable, low birefringent copolyimide films

Abstract

A class of solvent resistant, flexible copolyimide substrates having high optical transparency (>80% from 400 to 750 nm) that is retained after brief exposure to 300° C., near-zero birefringence (<0.001) and a maximum CTE of approximately 60 ppm/° C. is disclosed. The copolyimides are prepared from alicyclic dianhydrides, aromatic cardo diamines, and aromatic diamines containing free carboxyl groups. The substrates are manufactured from solutions of the copolyimides containing multifunctional epoxides in the form of single layer films, multilayer laminates and glass fiber reinforced composite films. The substrates can be used in the construction of flexible optical displays, and other microelectronic and photovoltaic devices that require their unique combination of properties.

Claims

1. A transparent, flexible film for use as a substrate in an optical display comprising: a copolyimide; and, a multifunctional epoxide, wherein the copolyimide is prepared from a mixture of dianhydrides and diamines, wherein at least one of the dianhydrides is an alicyclic dianhydride, at least one of the diamines is an aromatic cardo diamine, and at least one of the diamines is an aromatic diamine containing a free carboxylic acid group, and wherein the diamine containing the free carboxylic acid group is present in amounts greater than 10 mole percent and less than 20 mole percent of the total diamine mixture, and wherein the film has a birefringence of <0.001 and, upon exposure to a temperature of approximately 250° C. under reduced pressure for approximately 30 minutes, is solvent resistant when the film is immersed in organic solvents, wherein the copolyimide has the general structure: ##STR00030## wherein, x is 50 to 90 mol %; y is 0 to 30 mol %; z is 10 to 20 mol %; and n is 1 to 3; wherein AC is selected from the group consisting of: ##STR00031## wherein Ar.sub.1 is selected from the group consisting of: ##STR00032## wherein, n is 4, wherein R.sub.1, R.sub.2, R.sub.4, and R.sub.5 are selected from the group consisting of hydrogen, halogen, alkyl, substituted alkyl, alkoxy, substituted alkoxy, aryl, substituted aryl, ethynyl, phenylethynyl, alkyl ester, substituted alkyl esters, and combinations thereof, wherein R.sub.1, R.sub.2, R.sub.4, and R.sub.5 can be the same or different; wherein Ar.sub.2 is selected from the group consisting of: ##STR00033## wherein p is 4, and wherein R.sub.6, R.sub.7, and R.sub.8, are selected from the group consisting of hydrogen, halogen, alkyl, substituted alkyl, nitro, cyano, thioalkyl, alkoxy, aryl, substituted aryl, alkyl ester, substituted alkyl esters, and combinations thereof, wherein R.sub.6, R.sub.7, and R.sub.8 can be the same or different; wherein G.sub.2 is selected from the group consisting of a covalent bond, a CH.sub.2 group, a C(CH.sub.3).sub.2 group, a C(CF.sub.3).sub.2 group, a C(CX.sub.3).sub.2 group wherein X is a halogen, a CO group, an O atom, a S atom, a SO.sub.2 group, a Si (CH.sub.3).sub.2 group, a —C(CH.sub.3).sub.2-aryl-(CH.sub.3).sub.2C— group, and a OZO group wherein Z is a aryl group or a substituted aryl group; wherein Ar.sub.3 selected from the group consisting of: ##STR00034## wherein t=1 to 3, wherein R.sub.9, R.sub.10, and R.sub.11 are selected from the group consisting of hydrogen, halogen, alkyl, substituted alkyl, alkoxy, substituted alkoxy, aryl, substituted aryl, alkyl ester, substituted alkyl esters, and combinations thereof, wherein R.sub.9, R.sub.10, and R.sub.11 can be the same or different; wherein G.sub.3 is selected from the group consisting of a covalent bond; a CH.sub.2 group; a C(CH.sub.3).sub.2 group; a C(CF.sub.3).sub.2 group; a C(CX.sub.3).sub.2 group, wherein X is a halogen; a CO group; an O atom; a S atom; a SO.sub.2 group; a Si(CH.sub.3).sub.2 group; and an OZO group, wherein Z is an aryl group or a substituted aryl group.

2. The film of claim 1, wherein the amount of multifunctional epoxide is 2 to 10 wt % based on the weight of the copolyimide.

3. The film of claim 1, wherein the transmittance from 400 to 750 nm is >80%, and the maximum CTE is approximately 60 ppm/° C.

4. The film of claim 1, wherein the alicyclic dianhydride is selected from the group consisting of 1,2,3,4 cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, and bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride.

5. The film of claim 1, wherein the aromatic cardo diamine is selected from the group consisting of 9, 9-bis(4-aminophenyl)fluorene, 9, 9-bis(4-amino-3-fluorophenyl)fluorene, and 9, 9-bis(4-amino-3-methylphenyl)fluorene.

6. The film of claim 1, wherein the mixture of aromatic diamines contains a non-cardo aromatic diamine.

7. The film of claim 1, wherein the aromatic diamine containing a free carboxylic acid group is selected from the group consisting of 3,5-daminobenzoic acid and 4,4′-diaminodiphenic acid.

8. The film of claim 1, wherein the multifunctional epoxide is selected from the group consisting of structures (II), (III) and (IV): ##STR00035## wherein x>1 and R is selected from the group consisting of: ##STR00036## wherein the cyclic structure is selected from the group consisting of: ##STR00037## wherein n>1 and R is an alkyl or aryl group.

9. The film of claim 8, wherein the multifunctional epoxide is selected from the group consisting of diglycidyl 1,2-cyclohexanedicarboxylate, triglycidyl isocyanurate, tetraglycidyl 4,4′-diaminophenylmethane, 2,2-bis(4-glycidyloxylphenyl)propane, 7H-indeo[1,2-b:5,6-b]bisoxireneoctahydro, and epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate.

10. A transparent, flexible substrate comprising a free standing film of claim 1 that is at least approximately 25 microns thick.

11. A multilayer, transparent, flexible substrate comprising a layer prepared from the film of claim 1 and a glass layer.

12. The substrate of claim 11, wherein the film is at least approximately 5 microns thick and the glass layer is at least approximately 25 microns thick.

13. The substrate of claim 11, wherein the transmittance from 400 to 750 nm is >80% and the maximum CTE is approximately 60 ppm/° C.

14. A glass fiber reinforced, transparent, flexible copolyimide substrate comprising the film of claim 1 and a glass mat.

Description

DETAILED DESCRIPTION

(1) It has been discovered that soluble copolyimides with Tgs>400° C. can be used in the manufacture of solvent resistant, transparent, flexible substrates with near zero birefringence. In particular, it has been found that copolyimides that are prepared from alicyclic dianhydrides; aromatic, cardo diamines; and aromatic diamines containing carboxyl groups can be used along with multifunctional epoxides in the manufacture of transparent substrates (transmittance >80% at 400 nm to 750 nm with a birefringence of <0.001 and a maximum CTE of approximately 60 ppm/° C. In some cases, mixtures of alicyclic dianhydrides may be used. The preferred alicyclic dianhydride is 1,2,4,5-cyclohexanetetracarboxylic dianhydride (H-PMDA). The preferred cardo diamines are 9,9′-bis(4-aminophenyl)fluorene (FDA) and its substituted derivatives. The preferred diamines containing free carboxylic acid groups are 3,5-diaminobenzoic acid (DAB) and 4,4′-diaminodiphenic acid (DADP). In some cases, it may be desirable to substitute some of the cardo diamine with a non-cardo, aromatic diamine. The monomers can be polymerized in high boiling solvents, such DMAC, NMP, and m-cresol, which can contain an imidization catalyst, such as isoquinoline, at elevated temperatures to directly yield the imidized polymer. Solvents should not be used that undergo degradation with the development of color after extended heating. The polymerization mixture may also contain reagents such as toluene and xylene that form an azeotrope with water that can be distilled from the reaction mixture. Alternatively, the monomers can be polymerized in polar aprotic solvents, such as DMAC or NMP, below 50° C. to yield a polyamic acid that is imidized either chemically or thermally. In chemical imidization a mixture of an imidization catalyst, such as a tertiary amine, and a dehydration agent, such as an aliphatic dianhydride, is added to the polymerization solution. The preferred imidization catalysts are triethylamine, pyridine, substituted pyridine derivatives, and isoquinoline. The preferred dehydration agents are acetic anhydride and perfluoroacetic anhydride. Imidization can also be carried out by a combination of these two methods. Although, the copolyimides obtained from these procedures have very high degrees of imidization, they are soluble in volatile organic solvents. In all of the polymerization procedures an excess of dianhydride is normally used so that the copolyimide is end-capped with anhydride groups. Amine end groups can degrade during the curing process leading to the development of color. A molar ratio of dianhydride to the total amount of diamines of approximately 1.001 to 1.01 is preferred.

(2) The copolyimides are isolated by precipitation in a non-solvent, such as an alcohol. The preferred non-solvents are methanol and ethanol. A film casting solution is then prepared by dissolving the polymer and a multifunctional epoxide in a polar solvent, such as DMAC, NMP and cyclopentanone. In some cases, it may be possible to avoid the polymer isolation step and to add the multifunctional epoxide directly to the polymerization mixture. The epoxide must display minimum color. Colorless epoxides are preferred. The most preferred epoxide is triglycidyl isocyanurate (TG). The minimum amount of epoxide is used that results is a colorless film that displays solvent resistance after being heated at less than approximately 250° C. for less than approximately 30 minutes. It too little is used the film will not become solvent resistant. If an excessive amount of epoxide is used, the film will yellow when heated at elevated temperatures. The preferred amount of epoxide is approximately 2 to approximately 10 wt % of the weight of the polyamide. The most preferred amount is 4 to 6 wt %. The greater the number of epoxy groups in the multifunctional epoxide the smaller the amount that has to be used. The fact that the films become solvent resistant after heating at less than approximately 250° C. is a result of the pendent carboxyl groups located along the copolyimide backbone. If carboxyl groups are not present or too few are present, the films will not display solvent resistance. However, the amount of these groups present must be limited. An excessive amount results in a polymer that: 1) cannot be made solvent resistant even through the use of excess amounts of a multifunctional epoxides; 2) is moisture sensitive; and 3) displays too high a CTE and a reduced thermal stability. The carboxyl group content is controlled by controlling the amount of diamine that contains carboxyl groups that is used in the preparation of the polymer. The preferred amount of this diamine is 5 to 50 mol % of the diamine mixture. The most preferred amount is 10 to 20 mol %. The greater the number of carboxyl groups in the diamine, the less the amount that is required to enhance the curing process.

(3) Surprisingly, the carboxyl group undergoes reaction with the epoxide at elevated temperatures without the development of color. It has been discovered that other functional groups that react with epoxy groups such as hydroxyl groups promote curing, but at the expense of color development. The curing process is carried out under reduced pressure or in an inert atmosphere so that no change in the film properties occurs. It is especially important that the process is carried out without any oxidative degradation that leads to the development of color.

(4) The copolyimides are prepared from alicyclic dianhydrides selected from the group:

(5) ##STR00009##
Wherein, AC is selected from the group:

(6) ##STR00010##

(7) Particularly useful dianhydrides are:

(8) 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA)

(9) ##STR00011##

(10) 1,2,3,4-Cyclopentanetetracarboxylic dianhydride (CPDA)

(11) ##STR00012##

(12) 1,2,3,4-Cyclohexanetetracarboxylic dianhydride (H-PMDA)

(13) ##STR00013##

(14) Bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BODA)

(15) ##STR00014##

(16) And cardo, aromatic diamines selected from the group:

(17) ##STR00015## wherein, n is 4; and wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 are selected from the group comprising hydrogen, halogen (fluoride, chloride, bromide, and iodide), alkyl, substituted alkyl such as halogenated alkyls, alkoxy, substituted alkoxy such as halogenated alkoxy, aryl, or substituted aryl such as halogenated aryls, ethynyl, phenylethynyl, alkyl ester and substituted alkyl esters, and combinations thereof. It is to be understood that R.sub.1, R.sub.2, R.sub.3, R.sub.4, and R.sub.5 can be the same or different.

(18) Particularly useful cardo diamines are:

(19) 9,9′-Bis(4-aminophenyl)fluorene (FDA)

(20) ##STR00016##

(21) 9,9′-Bis(4-amino-3-fluorophenyl)fluorene (FFDA)

(22) ##STR00017##

(23) 9,9′-Bis(4-amino-3-ethylphenyl)fluorene (MeFDA)

(24) ##STR00018##

(25) And aromatic diamines selected from the group:

(26) ##STR00019## wherein p is 4, and wherein R.sub.6, R.sub.7 and R.sub.8 are selected from the group comprising hydrogen, halogen (fluoride, chloride, bromide, and iodide), alkyl, substituted alkyl such as halogenated alkyls, alkoxy, substituted alkoxy such as a halogenated alkoxy, aryl, substituted aryl such as halogenated aryls, alkyl ester, and substituted alkyl esters, and combinations thereof. It is to be understood that R.sub.6, R.sub.7, and R.sub.8 can be the same or different; and wherein G.sub.2 is selected from a group comprising a covalent bond; a CH.sub.2 group; a C(CH.sub.3).sub.2 group; a C(CX.sub.3).sub.2 group, wherein X is a halogen; a CO group; an O atom; a S atom; a SO.sub.2 group; a Si(CH.sub.3).sub.2 group, a —C(CH.sub.3).sub.2-aryl-(CH.sub.3).sub.2C—; and an OZO group, wherein Z is an aryl group or substituted aryl group, such as a phenyl group, a biphenyl group, and a perfluorobiphenyl group.

(27) And aromatic diamines containing a pendent carboxyl group selected from the group:

(28) ##STR00020## wherein, m is 1 to 2, wherein t is 1 to 4, and wherein R.sub.9, R.sub.10, R.sub.11 are selected from the group comprising hydrogen, halogens (fluoride, chloride, bromide, and iodide); alkyl groups; substituted alkyl groups such as halogenated alkyl groups; alkoxy groups; substituted alkoxy groups such as halogenated alkoxy groups; aryl groups; substituted aryl groups such as halogenated aryls; alkyl ester groups; and substituted alkyl ester groups; and combinations thereof. It is to be understood that R.sub.9, R.sub.10, and R.sub.11 can be the same or different. G.sub.1 is selected from a group comprising a covalent bond; a CH.sub.2 group; a C(CH.sub.3).sub.2 group; a C(CX.sub.3).sub.2 group, wherein X is a halogen; a CO group; an O atom; a S atom; a SO.sub.2 group; a Si(CH.sub.3).sub.2 group; and an OZO group, wherein Z is a aryl group or substituted aryl group, such as a phenyl group; a biphenyl group, and a perfluorobiphenyl group.

(29) Representative and illustrative examples of the useful aromatic diamines with pendant free carboxylic acid groups are:

(30) 4,4′-Diaminodiphenic acid (DADP);

(31) ##STR00021##

(32) 3,5-Diaminobenzoic acid (DAB).

(33) ##STR00022##

(34) And, the multifunctional epoxide is selected from the group with the general structures (II), (III) and (IV):

(35) ##STR00023## wherein x>1 and R is selected from the group

(36) ##STR00024## wherein the cyclic structure is selected from the group

(37) ##STR00025## wherein n>1 and R is an alkyl or aryl group.

(38) Representative and illustrative examples of multifunctional compounds containing epoxy groups particularly useful are:

(39) Diglycidyl 1,2-cyclohexanedicarboxylate (DG)

(40) ##STR00026##

(41) Triglycidyl isocyanurate (TG)

(42) ##STR00027##

(43) Tetraglycidyl 4,4′-diaminophenyl methane (TTG)

(44) ##STR00028##
wherein n>1 and R is an alkyl or aryl group

(45) ##STR00029##

(46) Substrates can be prepared as single layer, films; as multi-layer laminates comprising a copolyimide layer and a thin glass layer; and as glass-reinforced composite films. The single layer films can be prepared by solution casting techniques known to those skilled in the art from solutions of the copolyimides containing multifunctional epoxides. Both batch and continuous processes, such as a roll-to-roll process, may be used. The viscosity of the solution is adjusted by adjusting the solids concentration and the polymer molecular weight so that optimum films may be produced with the equipment used. Solution viscosities of 10 to 1000 poises are preferred, but not always required depending on the casting equipment. The multilayer laminates can be prepared in one step by solution casting a layer of the copolyimide/multifunctional epoxide composition on thin glass films. Additives may be used to increase the adhesion of the copolyimide to the glass. The laminates may also be prepared in a multistep process, wherein a copolyimide layer is first solution cast on a carrying tape such as a polyester film. The combination is then laminated to the glass film so that the copolyimide layer adheres to the glass. The carrying tape is removed prior to or during the construction of the flat panel display. In the preparation of glass-reinforced composite films the solutions containing the copolyimide and the multifunctional epoxide are applied to a woven glass mat. It should be understood that is all of these processes the formation of the film is accomplished by the removal of solvent at elevated temperatures. In most cases, the film is formed at temperatures less than approximately 200° C. The formed film is then heated at approximately 200° C. to approximately 250° C. for less than approximately 30 minutes. When this process is carried out in a continuous fashion where the solution is cast on an endless belt the passes through heated zones, the heating steps may not be distinguishable.

(47) The substrates can also be prepared by solution casting techniques from solutions of copolyimide precursors, i.e. polyamic acids. In this case, the conversion of the polyamic acid to the copolyimide is carried out chemically, thermally or combinations of both during or subsequent to the casting process. A continuous, roll-to-roll process whereby the polyamic acid is mixed with a chemical imidization mixture immediately prior to casting on an endless belt, which passes through heated zones, can be used to prepare single layer substrates, copolyimide film/glass laminates, and glass reinforced copolyimide composite films. The multifunctional epoxide can be added before or subsequent to the addition of the imidization mixture. Alternatively, the process can be carried out without the addition of an imidization mixture, so that only thermal imidization occurs as the belt passes through the heated zones.

(48) In order to simplify the construction of a flexible display, other functional and non-functional layers may be cast on or laminated to the substrate. For example, a gas barrier layer may be adhered.

EXAMPLES

(49) Film solvent resistance. The solvent resistance of the film was determined by immersing it in a selected solvent for 30 minutes at room temperature. The film was considered insoluble and solvent resistant if it were substantially free of surface wrinkles, swelling, or any other visible damage after immersion.

(50) Film thermal properties. The film thermal properties were determined using a TA Instruments Q400 Thermal Mechanical Analyzer. The reported CTEs are the average CTE between 30 and 300° C.

(51) Film birefringence. The dry polymer was dissolved in an organic solvent with a solids content between 10˜15%. After filtration, the solution was cast on a glass substrate using a doctor blade. The resulting film was dried at 100° C. under reduced pressure. The polymer film was removed from the glass by dipping the substrate glass in water. Films ranging from approximately 10 μm to >25 μm thick were prepared in this manner. Birefringence was determined using a 10 μm thick freestanding film with a Metricon Prism Coupler 2010/M. The birefringence is reported as Δn=n.sub.z−n.sub.x,y.

(52) Film transparency. Transparency was measured by determining the transmittance of a 10 μm thick film from 400 to 750 nm with a UV-Visible spectrometer (Shimadzu UV 2450). The transmittance was determined before and after the film was heated at a given temperature and a given period of time under reduced pressure. The transmittance is reported as the minimum transmittance at 400 nm.

Example 1

(53) This example illustrates the procedure to prepare a copolyimide with pendent carboxyl groups.

(54) To a 250 ml, three necked round bottom flask equipped with a mechanical stirrer, a nitrogen inlet and an outlet connected to a gas bubbler were added 1,2,4,5,-cyclohexanedicarboxylic dianhydride (H-PMDA) (4.5286 g 20.2 mmol), 9,9′-bis(4-aminophenyl)fluorene (FDA) (5.5750 g, 16.0 mmol), 3,5-diaminobenzoic acid (DAB) (0.6086 g, 4.0 mmol) and m-cresol (50 ml). (Mol ratio H-PMDA/FDA/DAB=1.01/0.80/0.20). The mixture was heated briefly at 120° C. until the solids dissolved. The mixture was stirred at room temperature for 5 hours, and then heated at 210° C. overnight. Upon cooling, the polymer solution was poured into methanol, and the polymer precipitate that formed was collected by filtration, extracted with methanol several times, and dried under reduced pressure at 200° C. for 24 hours.

Example 2

(55) This example illustrates the procedure to prepare copolyimide films containing a multifunctional epoxide.

(56) The polymer was prepared according to the procedure described in Example 1. The dried polymer was mixed with TG (weight ratio of 95/5) in DMAC so as to form a solution containing 10% solids. The solution was cast on a glass plate using a doctor blade at room temperature. The film was dried at 100° C. under reduced pressure for 12 hours. The films were made solvent resistant by heating at the specified temperatures for the specified times under reduced pressure (Table 1).

(57) Copolymers were prepared by the procedure described for Example 1 from mixtures of H-PMDA, BODA, FDA, FFDA MeFDA, DAB and DADP containing different mol ratios of the components (Tables 1-5). The components and amounts used were selected so that the resulting copolyimide had a Tg>400° C. The copolymers were mixed with different amounts of TG (wt %) in DMAC. The solutions were cast into films that were heated at specified temperatures for specified periods of time under reduced pressure. After heating, samples of the films were immersed in NMP for 30 minutes at room temperature. The effect of the solvent on the films is shown in Table 1.

(58) TABLE-US-00001 TABLE 1 NMP Resistance of Copolyimide Films After Heating at 250° C. Cure 5 wt % TG 10 wt % TG Polymer Films (Mol Time Dispersed in Dispersed in ratios of components) (Min) Copolyimide Film Copolyimide Film H-PMDA/FDA/DAB 30 Soluble Soluble (1.01/0.95/0.05) H-PMDA/FDA/DAB 30 Swollen Swollen (1.01/0.90/0.10) H-PMDA/FDA/DAB 30 Swollen Swollen (1.01/0.85/0.15) H-PMDA/FDA/DAB 10 Insoluble Insoluble (1.01/0.80/0.20) H-PMDA/FFDA/DADP 10 Insoluble Insoluble (1.01/0.90/0.10) BODA/FDA/DAB 10 Insoluble Insoluble (1.01/0.80/0.20) BODA/FFDA/DAB 10 Insoluble Insoluble (1.01/0.80/0.20) BODA/MeFDA/DAB 10 Insoluble Insoluble (1.01/0.80/0.20) BODA/FFDA/DADP 10 Insoluble Insoluble (1.01/0.90/0.10)

(59) TABLE-US-00002 TABLE 2 Optical Properties of Copolyimide Films Before and After Heat Treatment After Heating at 250° C. Amount Initial for 10 Min Polymer Films (Mol TG T % at T % at ratios of components) Added Δn 400 nm Δn 400 nm H-PMDA/FDA/DAB 5% 0.0008 88 −0.0004 85 1.01/0.80/0.20 10%  −0.0002 87 0.0002 85 H-PMDA/FFDA/DADP 5% −0.0002 83 0.0000 80 1.01/0.90/0.10 BODA/FDA/DAB 5% −0.0002 86 0.0001 84 1.01/0.80/0.20 BODA/FFDA/DAB 5% 0.0003 88 −0.0001 85 1.01/0.80/0.20

(60) TABLE-US-00003 TABLE 3 Thermal Properties of a Copolyimide After Heating at 250° C. for 10 Minutes Polymer Films (Mol ratios of components) Amount TG Added Tg, ° C. CTE, ppm/° C. H-PMDA/FDA/DAB  0% 425 50 1.00/0.80/0.20 10% 440 49

(61) TABLE-US-00004 TABLE 4 Optical Properties of a Copolyimide Film After Heating at Elevated Temperature Transmittance, % After heating After heating Polymer Films (Mol Amount at 250° C. for at 300° C. for ratios of components) TG Added 10 Minutes 10 Minutes H-PMDA/FDA/DAB  5% 85 84 1.01/0.80/0.20 10% 85 83

(62) TABLE-US-00005 TABLE 5 Tg and CTE of Uncured Copolyimides Polymer Films (Mol ratios of components) Tg, ° C. CTE, ppm/° C. H-PMDA/FDA/DADP 441 48 1.01/0.90/0.10 H-PMDA/FFDA/DADP 423 61 1.01/0.90/0.10 BODA/FDA/DADP 445 52 1.01/0.90/0.10 BODA/FFDA/DADP 449 55 1.01/0.90/0.10 BODA/MeFDA/DADP 439 58 1.01/0.90/0.10

COMPARATIVE EXAMPLES

Comparative Example 1

(63) The copolyimide prepared in Example 1 was cast into film from a 10 wt % DMAC solution that did not contain a multifunctional epoxide. The film was heated at 250° C. for 30 minutes under reduced pressure. The film dissolved when immersed in NMP at room temperature.

(64) The embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatus may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. Although the description above contains much specificity, this should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of this invention. Various other embodiments and ramifications are possible within its scope.

(65) Furthermore, notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.