Melt-moldable crystalline polyimide polymer

Abstract: A crystalline polyimide polymer contains at least 30 mol % of repeating imide units of the formula:- (in which X is a single bond, an oxygen or sulphur atom or a group -CO- or -SO₂-), optionally together with one or more other repeating imide units; the polymer having an inherent viscosity of from 0.1 to 5 dl/g as measured in a concentration of 0.5g/dl in concentrated sulphuric acid at a temperature of 30 ± 0.01 °C. The polymer is prepared by reacting appropriate dianhydrides and diamines to form a precursor which is subsequently imidized.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a melt-moldable crystalline polyimide polymer. Description of the Related Art In general, since polyimides are organic high-molecular weight compounds having a high heat resistance and also superior electrical characteristics and mechanical characteristics, they have been broadly used as protecting materials, insulating materials, in the field of electronic equipments and also adhesives, films, structural units, etc. However, conventional polyimides have high melting points or glass transition points and these temperatures often exceed their thermal decomposition temperatures or are close thereto; hence it has generally been difficult to subject them to melt-molding.Thus, as current molding processes for polyimides, molding processes for thermosetting resins have been mostly employed such as processes for coating and baking a precursor solution of polyimides or a soluble polyimide solution or processes for subjecting powdery polyimide polymers to compression molding, etc. Accordingly, if a polyimide polymer to which extrusion molding or injection molding as molding processes for thermoplastic resins is applicable is obtained, it is possible to improve the productivity of polyimide molded products and also obtain various molded products therefrom; hence the economical effect will be great. Thus, meltable polyimide polymers have often been proposed. For example, U.S. Patent 4558110 discloses a crystalline silicone imide copolymer. However, this copolymer has a m.p. of 140 -210°C according to its Examples; hence it cannot help regarding the copolymer as having improved its processability at the cost of its heat resistance specific of polyimides. Further, European patent application publication No. 200204 discloses a specific pyromellitic imide copolymer as a meltable polyimide copolymer, and also discloses that the copolymer is moldable into film by melt-press at 400°C, and an effectiveness brought about thereby, but its melting point is not shown and whether the copolymer is crystalline or not is unclear. FR-A-2 578 545 discloses that a colourless transparent polyimide shaped article may be obtained using an aromatic diamine having the amino groups in the meta-position. As described above, industrial need for meltable polyimide polymers is great, but it is the present status that such polymers are still being groped for. SUMMARY OF THE INVENTION The object of the present invention is to provide a melt-moldable crystalline polyimide polymer having a high melting point lower than its thermal decomposition temperature. The present invention resides in: a melt-moldable, crystalline polyimide polymer having an inherent viscosity of 0.1 to 5 dℓ/g as measured in a concentration thereof of 0.5 g/dℓ in concentrated sulfuric acid at a temperature of 30 ± 0.01°C, and having a melting point of 300° to 388°C as measured by means of a differential scanning calorimenter at a heating rate of 5°C/minute; which polymer comprises at least 30 moles% of imide repeating units of the formula together with imide repeating units of the formula: and also optionally comprises at least one of the repeating units of the formulae: and further optionally comprises an imide repeating unit of the formula: (wherein R 11 represents a tetravalent organic group; R 12 represents divalent organic group) other than a repeating unit of the formula: (wherein X is a single bond, an oxygen or a sulphur atom, or a group CO- or -SO 2 -); or comprises (B) at least 30 mole% (based on the polymer) of imide repeating units of formula (II) and also comprises at least one of the repeating units of the formulae (IV), (V), or (XIV) and further optionally comprises an imide repeating unit of formula (XVII) other than a repeating unit of formula (I). The polyimide polymer may be prepared by a process which comprises feeding into a reaction vessel appropriate amounts of a diacid anhydride of the formula: a diamine of the formula: together with a diacid anhydride of the formula: and/or one or more diamines of the formulae or and, optionally, one or more diacid anhydrides of the formula: in which R 11 is a tetravalent organic group such that the anhydride is other than any of andrides (a) or (c); and, suitably, one or more diamine of the formula: H 2 N - R 12 - NH 2 in which R 12 is a divalent organic group such that the diamine is other than any of diamines (b), (d) or (e); reacting the anhydrides and amines at a temperature of from 0 to 200°C from 0.2 to 20 hours in the presence of a solvent; and imidizing the resulting polyimide precursor to give a crystalline polyimide polymer. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 shows the infrared absorption spectra of a polymer obtained in Example 1. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The average molecular weight of the polyimide polymer of the present invention refers to that corresponding to an inherent viscosity within a range of 0.1 to 5 dℓ/g as measured under the above-mentioned specified conditions. The above inherent viscosity (η inh) referred to in the present invention is as defined under the above measurement conditions, and more particularly it is expressed by the equation η inh = ℓn η/η 0 C wherein η represents a value obtained by measuring a polymer in its concentration of 0.5 g/dl in concentrated sulfuric acid at a temperature of 30 ± 0.01°C by means of Ubbellohde viscometer; η 0 represents a value obtained by measuring concentrated sulfuric acid at the same temperature by means of Ubbellohde viscometer; and C represents 0.5 g/dℓ. The imide repetition units expressed by the formula (II) with (III), (IV), (V) or (XIV) form 30 to 100% by mol in the polymer of the present invention. If the percentage is lower than 30% by mol, it is difficult to obtain polymers having points lower than 450°C. In the repeating units of formula (XVII) R 11 may, for example, be a tetravalent carbon cyclic aromatic group or alicyclic group and R 12 may, for example, represent an aliphatic group of 2 to 12 carbon atoms, an alicyclic group of 4 to 30 carbon atoms, an araliphatic group of 7 to 30 carbon atoms, a carbon cyclic aromatic group of 6 to 30 carbon atoms, a polysiloxane group expressed by the formula wherein R 4 independently represents -(CH 2 ) r -, wherein r represents an integer of 1 to 4, R 5 independently, represents an alkyl group of 1 to 6 carbon atoms, phenyl group or an alkyl-substituted phenyl group of 7 to 12 carbon atoms and ℓ represents a value of 1 ≦ ℓ ≦ 100, or a group expressed by the formula wherein R 3 represents an aliphatic group, an araliphatic group each of 8 carbon atoms or less or hydrogen atom Still more concrete examples of repeating units of formula (XVII) are as follows: Next, preparation of the polyimide polymers of the present invention will be described. Examples of the compounds expressed by the above formula (IX) are: and Further, an example of the compounds expressed by the above formula (X) is In order to produce a polyimide copolymer comprising the repetition unit of the formula (II) and also other imide repetition units, at least one of diacid anhydrides other than the diacid anhydride formula (a), such as pyromellitic dianhydride and/or at least one diamine other than the diamine of formula (b) such as 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl-methane, 3,3'-diaminodiphenyl sulfone, 2,2-bis[4-(4-aminophenoxy) phenyl] propane, and bis [4-(4-aminophenoxy)phenyl] sulfone, may be added to the above-mentioned diacid anhydrides and diamines and the mixture may be reacted together. Among these other diamines, addition of 3,4'-diamino-diphenyl ether particularly has a notable effect upon reduction in melting point. The imide repetition unit expressed by the formula (II) and imide repetition units other than the above may be bonded to each other either in block manner or random manner. In an embodiment of preparation of such copolymers, there is a process wherein 30% by mol or more based on the total diamines, of the diamine of formula (b) is reacted with 30% by mol or more based on the total diacid anhydrides, of the dianhydride of formula (a), followed by feeding to the resulting reaction liquid, at least one of diamines expressed by the formulae (d), (e) or (x) and at least one of diacid anhydrides expressed by the formulae (c) or (IX) and reacting these to obtain the precursor and imidize it. In another embodiment, there is a process wherein 30% by mol or more based on the total diamines, of the diamine of formula (b) is reacted with an almost equimolecular quantity to the above, of the dianhydride of formula (a), followed by feeding to the resulting solution, at least one of the other diamines and at least one of the other diacid anhydrides and reacting these to obtain a precursor and imidize it. In still another embodiment, there is a process wherein the anhydride of formula (a) is fed into a mixed solution of 30% by mol or more based on the total diamines, of the diamine of formula (b) with one or more of the other diamines, followed by reacting these to obtain a precursor and imidize it. In further another embodiment, there is a process wherein a mixture of 30% by mol or more based on the total diacid anhydrides, of the dianhydride of formula (a) with at least one of the other dianhydrides is fed into a solution of the diamine of formula (b) followed by reacting these to obtain a precursor and imidize it. Further, by repeating these operations with different raw materials, it is also possible to obtain multi-block copolymers. In the process, whatever polymerization process is employed, it is preferred that the quantity of the total diacid anhydrides and that of the total amines be almost equimolecular, whereby polymers having a high-molecular weight are easily obtained. According to the present invention, by preparing polyimides using a combination of particular polynuclear diacid anhydrides and polynuclear ethers, there are obtained crystalline polyimides having a melting point in the range of 300° to 388°C which is a practically highly valuable temperature range, without reducing heat resistance so much. The present invention will be described in more detail by way of Examples and Comparative examples. Example 1 (comparative) A 1 ℓ flask equipped with a stirrer, a dropping funnel, a thermometer, a condenser and a nitrogen gas-purging means was fixed in a constant temperature bath. After purging the inside of the flask with nitrogen gas, dehydrated and purified N-methyl-2-pyrrolidone (500 mℓ) and 1,3-bis(4-aminophenoxy)benzene (45.29 g) were fed into the flask, followed by dissolving these together with stirring, gradually adding to the resulting solution, 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (45.59 g) through the dropping funnel over 30 minutes to carry out reaction. During the period, the reaction temperature was 20 to 30°C. The reaction was further continued at this temperature for 10 hours to obtain a viscous varnish. This varnish was fed into a large quantity of acetone and the resulting deposited powder was filtered off to obtain a polyamic acid powder. This powder was heated in an oven at 300°C for one hour to obtain a polyimide polymer. This polymer exhibited a sharp endothermic peak at 402°C in the measurement of melting point by means of a differential scanning calorimeter and melted at the temperature. The fact that the melting point was exhibited as above evidences that this polymer is crystalline. Further, the inherent viscosity of this polymer in concentrated sulfuric acid was 1.8 dℓ/g. The infrared absorption spectra of this polymer are shown in Fig. 1. The above measurement of the melting point by means of a differential scanning calorimeter was carried out by using DSC-1500M (tradename of differential scanning calorimeter manufactured by Shinku Riko Company), raising the temperature at a rate of 5°C/min. and reading the top of the endothermic peak to render the reading as the melting point. This applies also to the succeeding Examples. Example 2 Example 1 was repeated except that to a solution obtained by dissolving 1,3-bis(4-aminophenoxy)benzene (44.24 g) as a diamine in N-methyl-2-pyrrolidone (500 mℓ) were added 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (22.26 g) and 3,4,3',4'-benzophenonetetracarboxylic acid dianhydride (24.38 g) each as a diacid anhydride each over 30 minutes, to obtain a viscous vanish. This varnish was treated as in Example 1 to obtain a polyimide polymer of the present invention having a m.p. of 327°C as measured by means of the differential scanning calorimeter and an inherent viscosity of 1.4 dℓ/g in conc. sulfuric acid. Example 3 Reaction and treatment were carried out in the same manner as in Example 2 except that 1,3-bis(4-aminophenoxy)benzene (44.65 g) as a diamine and 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (31.46 g) and 3,4,3',4'-benzophenonetetracarboxylic acid dianhydride (14.77 g), each as a diacid anhydride were used. The resulting polyimide polymer of the present invention had a melting point of 338°C as measured by the differential scanning calorimeter and an inherent viscosity of 1.7 dℓ/g in conc. sulfuric acid. Example 4 (comparative) Reaction was carried out in the same manner as in Example 1 except that 1,3-bis(4-aminophenoxy)benzene (20.23 g) and bis[4-(4-aminophenoxy)phenyl] sulfone (29.93 g), each as a diamine, were dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by adding to the solution, 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (40.72 g) as a diacid anhydride over 30 minutes, to obtain a viscous varnish. This varnish was added with stirring to a solution obtained by dissolving isoquinoline (4 g) and acetic anhydride (60 g) in N-methyl-2-pyrrolidone (1 ℓ), followed by subjecting the mixture to imidization reaction at 20° to 30°C for one hour to obtain a powdery polyimide polymer. This powder was filtered off, followed by drying it in an oven at 200°C for one hour and measuring its physical properties. This polymer had a m.p. of 405°C as measured by by the differential scanning calorimeter and an inherent viscosity of 0.5 dℓ/g in conc. sulfuric acid. Example 5 Reaction was carried out in the same manner as in Example 1 except that 1,3-bis(4-aminophenoxy)benzene (24.58 g) and 4,4'-diaminodiphenyl ether (16.83 g), each as a diamine, were dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by adding to the solution, 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (49.47 g) as a diacid anhydride, to obtain a viscous varnish. This varnish was uniformly applied onto an aluminum plate by means of a coater having a distance of 254 µm (10 mils) kept, followed by heating the resulting material in an oven at 100°C for one hour and successively at 300°C for one hour to form a thin film of a polyimide polymer of the present invention. This thin film was scraped off and subjected to measurement of physical properties. The polymer had a melting point of 388°C as measured by the differential scanning calorimeter and an inherent viscosity of 2.5 dℓ/g in conc. sulfuric acid. Example 6 (comparative) Reaction was carried out in the same manner as in Example 1 except that 1,3-bis(4-aminophenoxy)benzene (48.44 g) as a diamine was dissolved in N-methyl-2-pyrrolidone (500 mℓ), followed by keeping the solution at 20° to 30°C, adding to this solution, firstly pyromellitic acid dianhydride (18.07 g) as a diacid anhydride over 30 minutes, reacting the mixture for 2 hours, further adding 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (24.38 g) over 30 minutes and reacting the mixture for 10 hours, to obtain a viscous varnish, which was then treated in the same manner as in Example 1, to obtain a polyimide polymer having a m.p. of 410°C as measured by the differential scanning calorimeter and an inherent viscosity of 1.5 dℓ/g in conc. sulfuric acid. Example 7 (comparative) Example 1 was repeated except that 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (45.59 g) as a diacid anhydride and 1,4-bis(4-aminophenoxy) benzene (45.29 g) as a diamine were used, to obtain a polymer. This polymer had a m.p. of 440°C as measured by the differential scanning calorimeter and an inherent viscosity of 2.1 dℓ/g in conc. sulfuric acid. Examples 8 and 9 Various polyimide copolymers were prepared using raw materials indicated in Table 1 in N-methyl-2-pyrrolidone (500 mℓ), and the copolymers were treated in the same manner as in Example 1 and subjected to measurement of physical properties. The results are shown in Table 1. Example 8 Example 9 Raw material S-BDPA ( g ) 48.62 42.51 Diacid anhydride BTDA ( g ) - 5.82 Raw material TPE-R ( g ) 29.03 31.71 Diamine 3 · 4'-DDE ( g ) 13.23 10.84 M.P. (°C) 343 340 Inherent viscosity ( dℓ/g ) 1.6 1.6 Example Comparative 10 Reaction was carried out in the same manner as in Example 1 except that 3,4,3',4'-biphenyltetracarboxylic acid dianhydride (66.46 g) as a diacid anhydride and p-phenylenediamine (24.42 g) as a diamine were used, followed by post-treatment, to obtain a polyimide polymer powder. This polymer had an inherent viscosity of 2.0 dℓ/g in conc. sulfuric acid, but exhibited no melting point at 450°C or lower as measured by the differential scanning calorimeter and caused notable decomposition when the temperature was raised above 450°C. Example 11 Comparative Reaction was carried out in the same manner as in Example 1 except that pyromellitic acid dianhydride (47. 39g) as a diacid anhydride and 4,4'-diaminodiphenyl ether (43.50 g) as a diamine were used, followed by post-treatment to obtain a polyimide polymer powder. This polymer had an inherent viscosity of 1.5 dℓ/g in conc. sulfuric acid, but exhibited no melting point at 450°C or lower as measured by the differential scanning calorimeter and caused notable decomposition when the temperature was raised above 450°C. Example 12 Comparative Reaction was carried out in the same manner as in Example 1 except that pyromellitic acid dianhydride (38.83 g) as a diacid anhydride and 1,3-bis(4-aminophenoxy)benzene (52.05 g) as a diamine were used, followed by post-treatment to obtain a polyimide polymer powder. This polymer had an inherent viscosity of 1.7 dℓ/g in conc. sulfuric acid, but exhibited no melting point at 450°C or lower and caused notable decomposition when the temperature was raised above 450°C. Further, separately, when the polymer powder was heated on a hot plate and observed, neither fusion nor flow occurred at temperatures up to 450°C. Since the polyimide polymer of the present invention has a melting point in the temperature range of 300 to 388°C which range is practically highly valuable, the polymer has a practical effectiveness that extrusion molding or injection molding which has so far been applied to thermoplastic resins, but could not have been achieved by conventional polyimides has become possible. Further, the heat resistance of the polymer is not reduced so much as compared with conventional polyimides.

Claims: A melt-moldable, crystalline polyimide polymer having an inherent viscosity of 0.1 to 5 dℓ/g as measured in a concentration thereof of 0.5 g/dℓ in concentrated sulfuric acid at a temperature of 30 ± 0.01°C, and having a melting point of 300° to 388°C as measured by means of a differential scanning calorimeter at a heating rate of 5°C/minute; which polymer comprises (A) at least 30 mole% (based on the polymer) of imide repeating units of the formula together with imide repeating units of the formula: and also optionally comprises at least one of the repeating units of the formulae: and further optionally comprises an imide repeating unit of the formula: (wherein R 11 represents a tetravalent organic group; R 12 represents divalent organic group) other than a repeating unit of the formula: (wherein X is a single bond, an oxygen or a sulphur atom, or a group CO- or -SO 2 -) ; or comprises (B) at least 30 mole% (based on the polymer) of imide repeating units of formula (II) and also comprises at least one of the repeating units of the formulae (IV), (V), or (XIV) and further optionally comprises an imide repeating unit of formula (XVII) other than a repeating unit of formula (I). A polyimide polymer, as claimed in Claim 1, consisting of repeating units of formulae (II) and (III).

Inventors: KAWAMOTO TAKAO, KIKUTA KAZUTSUNE, KONOTSUNE SHIRO, KUNIMUNE KOUICHI, KAWAMOTO, TAKAO, KIKUTA, KAZUTSUNE, KONOTSUNE, SHIRO, KUNIMUNE, KOUICHI
Applicants: CHISSO CORP, CHISSO CORPORATION
Application year: 1988
Main classification: C08G73
IPC codes: C08G73