Process for producing parabanic acid ring-containing polymer

Abstract: A process for producing a parabanic acid ring-­ containing polymer, which comprises reacting a polycarbo­ diimide polymer with oxalyl chloride and then treating the reaction product with water.

Description: This invention relates to a novel polymer comprising parabanic acid ring units and carbodiimide units, and to a process for producing a parabanic acid ring-containing polymer. Polymers containing a parabanic acid ring of the following formula for example a polyparabanic acid resin having a structure of the following formula have a thermal resistance comparable to polyimide resins, excellent electrical insulation over a wide range of frequencies, and good rigidity, strength and other mechanical properties, and have recently attracted attention as highly functional resins. A prior known process for producing such a polyparabanic acid resin comprises reacting hydrogen cyanide with a diisocyanate to form a precursor polymer containing a 1,3-imidazolidine-1,3-diyl ring, and then hydrolyzing the precursor polymer (see Japanese Patent Publication No. 20960/1974). This method, however, has the defect of requiring dangerous hydrogen cyanide. The present inventors have made extensive invetigations on a method of producing a parabanic acid ring-containing polymer, which is free from the aforesaid defect, and have now found that the use of a polycarbodiimide polymer as a starting material can easily give a parabanic acid ring-containing polymer without the need for using dangerous hydrogen cyanide. According to this invention, there is provided a process for producing a polymer comprising parabanic acid ring units, which comprises reacting a polycarbodiimide polymer with oxalyl chloride and then treating the reaction product with water, thereby converting at least 50% of the carbodiimide linkages into parabanic acid ring units. The invention also provides a polymer comprising parabanic acid ring units and carbodiimide units, which polymer is obtainable from a process which comprises reacting a polycarbodiimide polymer with oxalyl chloride and then treating the reaction product with water, thereby converting at least 50% of the carbodiimide linkages into parabanic acid ring units. The polycarbodiimide polymer used as a starting material in the process of this invention is known per se or may be produced by a known method (see, for example, US-A-2,941,969; JP-A-33279/1972; J. Org. Chem., 28 , 2069-2075; Chemical Review, 1981, vol. 81, No. 4, 619-621). For example, it can be easily produced by condensation reaction of an organic diisocyanate involving elimination of carbon dioxide. The organic diisocyanate used for the production of polycarbodiimide polymer may be an aliphatic, alicyclic, aromatic or aromatic-aliphatic diisocyanate or a combination thereof. The polycarbodiimide polymer used in the method of this invention includes homopolymers or copolymers comprising at least one type of recurring unit represented by the following formula -R-N=C=N- (I) wherein R represents an aromatic diisocyanate residue. Specific examples of such polycarbodiimide polymers are those having the following recurring units. In the above formulae, n may be 2 to infinite. The polycarbodiimide polymer that can be used in this invention may include copolymers containing two or more types of the above recurring units. The molecular weight of the polycarbodiimide polymer is not particularly limited. Generally, polycarbodiimide polymers having a number average molecular weight of 1,000 to 100,000, particularly 10,000 to 60,000, are preferred. In accordance with the present invention, the polycarbodiimide polymer is first reacted with oxalyl chloride. The polycarbodiimide polymer, in the form of a pre-molded article such as a film, sheet or fiber, or a solid such as a powder, is immersed in oxalyl chloride or its solution, or is contacted with a vapor of oxalyl chloride. If desired, the polycarbodiimide polymer may be swollen beforehand by treatment with a solvent for the polycarbodiimide polymer, for example tetrachloroethylene, trichloroethylene, tetrahydrofuran, dioxane, monochlorobenzene, dichlorobenzene, dimethylformamide, N-methyl-2-pyrrolidione, dimethylacetamide, and dimethyl sulfoxide. Alternatively, the reaction may be accelerated by using the aforesaid swelling solvents for preparing the oxalyl chloride solution. The above reaction may also be carried out by dissolving the polycarbodiimide polymer in a suitable solvent such as tetrachloroethylene, trichloroethylene, tetrahydrofuran, dioxane, monochlorobenzene, dichlorobenzene, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone or dimethyl sulfoxide, and adding oxalyl chloride to the resulting solution. The reaction proceeds even at room temperature, but may be carried out at an elevated temperature of up to about 100 °C. Since, however, too much heat is likely to induce self-addition of the polycarbodiimide polymer, temperatures ranging from room temperature to about 50 °C are usually preferred. The amount of oxalyl chloride used cannot be determined generically because it will vary depending upon the extent to which the carbodiimide linkage (-N=C=N-) in the polycarbodiimide polymer is converted to the parabanic acid ring. Its suitable amount is at least 1 equivalent, preferably 1 to 1.5 equivalents, per equivalent of the carbodiimide linkage in the starting polycarbodiimide polymer. As a result of the above reaction, the carbodiimide linkage (-N=C=N-) is bonded to oxalyl chloride (COCl)₂ to change the recurring units of formula (I) to recurring units of the following formula wherein R is as defined. Substantially all of the recurring units of formula (I) in the starting polycarbodiimide polymer may be changed to the recurring units of formula (II). Alternatively, according to the properties desired of the final product, they may be partly changed to the recurring units of formula (II) to form a copolymer comprising the recurring units of formulae (I) and (II). The conversion may be changed freely by adjusting the conditions for the reaction between the polycarbodiimide polymer and oxalyl chloride. The precursor polymer containing the recurring units of formula (II) obtained as above is then treated with water to give the desired polymer containing parabanic acid ring units represented by the following formula wherein R is as defined above. This treatment with water may be carried out by contacting the solid precursor polymer obtained by the above reaction with water or (a water vapor), or by dissolving the precursor polymer in a suitable solvent such as dimethylformamide, N-methyl-2-pyrrolidone or dimethylacetamide and then reacting it with water. Room temperature suffices as the treating temperature, but as required, the reaction system may be heated up to about 100 °C. This leads to the efficient production of a polymer containing the parabanic acid ring units of general formula (II). At least 50 % of the carbodiimide linkages in the polycarbodiimide polymer are converted to parabanic acid ring units, but greater than 90% may be converted. Since the thermosetting carbodiimide group can be left in the resulting parabanic acid ring-containing polymer as can be seen from the method of its synthesis, the process of this invention permits production of parabanic acid ring-containing polymer in various grades unlike parabanic acid polymers produced in general. The parabanic acid ring-containing polymer can be obtained in various forms such as a film, a varnish, a powder (molding material), and a fiber. By utilizing its excellent thermal resistance and strength, the parabanic acid ring-containing polymer provided by this invention can be used in various applications as a flexible printed circuit (FPC) base film, an insulation tape, a thermally resistant paint, a connector and other electrical component parts, and thermally resistant fibers. Furthermore, by leaving part of the carbodiimide group in the polymer and crosslinking the polymer, it can be handled as a thermosetting resin unlike conventional parabanic acid polymers which have been able to be handled only as thermoplastic polymers. The process of the invention therefore further comprises thermosetting the polymer comprising parabanic acid ring units. The following examples specifically illustrate the present invention. EXAMPLE 1 A mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI; 80/20) was reacted in perchloroethylene at 120 °C for 4 hours together with a carbodiimidization catalyst (1-phenyl-3-methylphospholene oxide) to give a polycarbodiimide solution. A film (I) was prepared from this solution by the dry method. The film (I) was immersed in oxalyl chloride and left to stand at room temperature for 5 hours and then treated with water to give a film (II). Analysis of the films (I) and (II) by infrared spectro-scopy (IR) led to the determination that a peak at 2140 cm⁻¹ ascribed to the carbodiimide group decreased, and peaks at 1744 and 1380 cm⁻¹ ascribed to the carbonyl groups newly appeared. This shows that the carbodiimide was changed to parabanic acid (conversion 50 %, film thickness 25 micrometers). The properties of the films (I) and (II) are shown in Table 1. Film (I) Film (II) Density (g/cm³) 1.22 1.30 Tensile strength 0.11 GPa (11 kg/mm²) (11 kg/mm²) 0.11 GPa Young's modulus 0.30 GPa (300 kg/mm²) (330 kg/mm²) 0.30 GPa Elongation at yield 10 % 7 % Long-term thermal resistance 120 °C 180 °C Volume resistivity less than 10¹⁶ Ω/cm less than 10¹⁶ Ω/cm EXAMPLE 2 4,4'-Diphenylmethane diisocyanate (MDI) was reacted in THF together with a carbodiimidization catalyst at 70 °C for 15 hours to give a polycarbodiimide solution. A polycarbodiimide film (I) was prepared from the resulting solution by the dry method. The film (I) was immersed in oxalyl chloride and left to stand for 3 hours, and then treated with water to give a film (II). Analysis of the films (I) and (II) by IR gave the same results as in Example 1. The conversion to parabanic acid was 50 % (film thickness 25 micrometers). The properties of the films (I) and (II) are shown in Table 2. Film (I) Film (II) Density (g/cm³) 1.19 1.32 Tensile strength 0.08 GPa (8 kg/mm²) (8.5 kg/mm²) 0.085 GPa Young's modulus 2.0 GPa (200 kg/mm²) (220 kg/mm²) 2.2 GPa Elongation at yield 15 % 10 % Long-term thermal resistance 150 °C 180 °C Volume resistivity less than 10¹⁶ Ω/cm less than 10¹⁶ Ω/cm EXAMPLE 3 Diphenyl ether diisocyanate was reacted in THF together with a carbodiimidization catalyst at 70 °C for 20 hours to give a polycarbodiimide solution. A polycarbodiimide film (I) was prepared from the resulting solution by the dry method. A film (II) was prepared from the film (I) in the same way as in Example 2. The properties of the films (I) and (II) are shown in Table 3. Film (I) Film (II) Density (g/cm³) 1.21 1.32 Tensile strength 0.09 GPa (9 kg/mm²) (9.5 kg/mm²) 0.095 GPa Young's modulus 2.8 GPa (280 kg/mm²) (300 kg/mm²) 3.0 GPa Elongation at yield 15 % 10 % Long-term thermal resistance 150 °C 180 °C Volume resistivity less than 10¹⁶ Ω/cm less than 10¹⁶ Ω/cm EXAMPLE 4 o-Toluidine diisocyanate (TODI) was reacted in a chlorobenzene/THF mixed solvent together with a carbodiimidization catalyst at 85 °C for 10 hours to form a polycarbodiimide solution. A polycarbodiimide film (I) was prepared from the resulting solution by the dry method. A film (II) was prepared from the film (I) in the same way as in Example 1. The properties of the resulting films are shown in Table 4. Film (I) Film (II) Density (g/cm³) 1.23 1.32 Tensile strength 0.09 GPa (9 kg/mm²) (10 kg/mm²) 0.10 GPa Young's modulus 3 GPa (300 kg/mm²) (300 kg/mm²) 3 GPa Elongation at yield 10 % 7 % Long-term thermal resistance 150 °C 180 °C Volume resistivity less than 10¹⁶ Ω/cm less than 10¹⁶ Ω/cm EXAMPLE 5 1-Methoxy-2,4-phenylene diisocyanate was reacted in a perchloroethylene/dioxane mixed solvent together with a carbodiimidization catalyst at 120 °C for 4 hours to form a polycarbodiimide solution. A polycarbodiimide film (I) was prepared from the resulting solution by the dry method. A film (II) was prepared from the film (I) in the same way as in Example 1. The properties of the resulting films are shown in Table 5. Film (I) Film (II) Density (g/cm³) 1.24 1.32 Tensile strength 0.1 GPa (10 kg/mm²) (11 kg/mm²) 0.11 GPa Young's modulus 2.8 GPa (280 kg/mm²) (300 kg/mm²) 3.0 GPa Elongation at yield 15 % 10 % Long-term thermal resistance 140 °C 180 °C Volume resistivity ) less than 10¹⁶ Ω/cm less than 10¹⁶ Ω/cm EXAMPLE 6 The polycarbodiimide film (I) obtained in Example 1 was exposed to a saturated vapor of oxalyl chloride at room temperature for 4 to 5 hours, and then treated with water to give a film (II). The IR and properties of the resulting film (II) were measured, and the same results as in Example 1 were obtained. EXAMPLE 7 The polycarbodiimide film (I) obtained in Example 2 was exposed to a saturated vapor of oxalyl chloride at room temperature for 4 hours, and then treated with water to give a film (II). The IR and properties of the resulting film (II) were measured, and the same results as in Example 2 were obtained. EXAMPLE 8 The polycarbodiimide film (I) obtained in Example 3 was exposed to a saturated vapor of oxalyl chloride at room temperature for 5 to 6 hours, and then treated with water to give a film (II). The IR and properties of the resulting film (II) were measured, and the same results as in Example 3 were obtained. EXAMPLE 9 To the polycarbodiimide solution obtained in Example 1 was slowly added dropwise 1.5 equivalents, per equivalent of the carbodiimide group, of oxalyl chloride. When the mixture was stirred for 7 hours, a pale yellow precipitate formed. After filtration, the resulting precipitate was washed in warm water until it became neutral. The product was further washed several times with methanol, and the resulting pale yellow powder was subsequently dried in vacuum at 80 °C for 3 hours. IR analysis of the resulting powder showed that absorptions ascribed to parabanic acid appeared at 1744 and 1380 cm⁻¹, and the peak at 2140 ascribed to the absorption of the carbodiimide group decreased. The pale yellow powder was dissolved in N-methylpyrrolidone (NMP), and a film was prepared from the solution by the dry method. The properties of the film were measured, and the results are shown in Table 6. Parabanic acid conversion 60 % Density (g/cm³) 1.30 Tensile strength (9 kg/mm²) 0.09 GPa Young's modulus (300 kg/mm²) 3.0 GPa Elongation at yield 8 % Long-term thermal resistance 180 °C Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 10 To the polycarbodiimide solution obtained in Example 2 was slowly added dropwise a tetrachloroethylene solution of 1.3 equivalents, per equivalent of the carbodiimide group, of oxalyl chloride. When the mixture was stirred for 10 hours, a pale yellow precipitate formed. The precipitate was collected and treated in the same way as in Example 9. It was determined that the carbodiimide group was changed to parabanic acid. The resulting pale yellow powder was dissolved in NMP, and a film was prepared from the solution by the dry method. The properties of the film were measured, and the results are shown in Table 7. Parabanic acid conversion 80 % Density (g/cm³) 1.33 Tensile strength (11 kg/mm²) 0.11 GPa Young's modulus (280 kg/mm²) 2.80 GPa Elongation at yield 10 % Long-term thermal resistance 180 °C Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 11 The polycarbodiimide film (I) obtained in Example 1 was immersed at room temperature for 3 hours in a tetrachloroethylene solution of oxalyl chloride in an amount which was in a large excess with respect to the carbodiimide group. Then, the film was treated with water, and dried at 60 °C for 2 hours. The parabanic acid conversion of the resulting film was 50 %, and it had much the same properties as the film (II) in Table 1. The results show that treatment of the film with a swelling solvent makes the reaction proceed rapidly. EXAMPLE 12 The polycarbodiimide film (I) obtained in Example 2 was immersed at room temperature for 2 hours in a tetrachloroethylene solution of oxalyl chloride in an amount which was in a large excess with respect to the carbodiimide group. Then, the film was treated with water, and dried at 60 °C for 2 hours. The parabanic acid conversion of the resulting film was 50 %, and it had much the same properties as the film (II) in Table 2. The results shows that treatment of the film with a swelling solvent makes the reaction proceed rapidly. EXAMPLE 13 P-Phenylene diisocyanate was reacted in THF for 5 hours together with a carbodiimidization catalyst to obtain polycarbodiimide as a powder. The powder was immersed at room temperature for 10 hours in oxalyl chloride, and then treated with water. The powder was then washed with methanol, and dried in vacuum at 40 °C for 5 hours. IR analysis of the resulting powder showed that characteristic absorptions appeared at 1744 and 1380 cm⁻¹, and the absorption of the carbodiimide group at 2140 cm⁻¹ decreased. The powder was dissolved in NMP and a film was prepared from the solution by the dry method. The properties of the film are shown in Table 8. Parabanic acid conversion 70 % Tensile strength (8 kg/mm²) 0.08 GPa Young's modulus (240 kg/mm²) 2.40 GPa Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 14 Naphthylene diisocyanate was raected at 70 °C for 8 hours in THF together with a carbodiimidization catalyst to give a white powder of polycarbodiimide. The powder was immersed in oxalyl chloride at room temperature for 10 hours, and treated with water. It was then washed with methanol and dried in vacuum at 40 °C for 5 hours. IR analysis of the resulting powder showed that characteristic absorptions appeared in the vicinity of 1740 and 1380 cm⁻¹. This demonstrates that the the diisocyanate was changed to parabanic acid. The powder was dissolved in NMP, and a film was prepared from the solution by the drying method. The properties of the film are shown in Table 9. Parabanic acid conversion 80 % Tensile strength (6 kg/mm²) 0.06 GPa Young's modulus (280 kg/mm²) 2.8 GPa Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 15 MDI was reacted in tetrachloroethylene at 120 °C for 6 hours to give a white powder of polycarbodiimide. The powder was immersed at room temperature for 5 hours in a tetrachloroethylene solution of oxalyl chloride in an amount which was in a large excess with respect to the carbodiimide group, and then treated with warm water. The powder was then washed with methanol, and dried in vacuum at 40 °C for 6 hours. IR analysis of the resulting powder showed that the characteristic absorption of parabanic acid was seen, and most of the characteristic absorption of the carbodiimide group disappeared. The powder was dissolved in NMP and a film was prepared from the solution by the dry method. The properties of the film are shown in Table 10. Parabanic acid conversion above 90 % Tensile strength (11 kg/mm²) 0.11 GPa Young's modulus (250 kg/mm²) 2.50 GPa Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 16 Cyclohexyl diisocyanate was reacted in THF at 70 °C for 10 hours to give a white powder of polycarbodiimide. The powder was immersed at room temperature for 5 hours in THF containing oxalyl chloride in an amount which was in a large excess with respect to the carbodiimide group, and after filtration the resulting powder was washed until it no longer gave a smell of oxalyl chloride. It was dried in vacuum at 30 °C for 5 hours. IR analysis of the resulting pale yellow powder showed that the absorption ascribed to the carbodiimide group mostly disappeared, and an absorption based on C-Cl newly appeared near 750 cm⁻¹. This powder is therefore considered to be a chloro adduct which is a precursor of parabanic acid. The powder was dissolved in NMP. When the solution was put in water, the powder changed to polyparabanic acid while evolving hydrogen chloride gas. IR analysis showed that the absoprtion based on C-Cl near 750 cm⁻¹ disappeared, and the absorptions of parabanic acid appeared near 1744 and 1380 cm⁻¹. The powder was dissolved in NMP, and a film was prepared from the solution by the dry method. The properties of the film ore shown in Table 11. Parabanic acid conversion 80 % Tensile strength (7 kg/mm²) 0.07 GPa Young's modulus ( 250 kg/mm²) 2.50 GPa Solder bath test (260 °C, 15 sec.) acceptable Volume resistivity less than 10¹⁶ Ω/cm EXAMPLE 17 Polycarbodiimide fibers (I) were prepared by a dry spinning method from a polycarbodiimide solution synthesized by the method of Example 1. The fibers were treated with oxalyl chloride and water by the same method as in Example 1 to give fibers (II). The properties of the fibers (I) and (II) are shown in Table 12. Fibers (I) Fibers (II) Fiber diameter µm 100 100 Tensile strength GPa (kg/mm²) 1 (100) 1 (100) Young's modulus GPa (kg/mm²) 15 (1,500) 15 (1,550) Elongation at yield % 15 13 EXAMPLE 18 The polycarbodiimide fibers obtained in Example 17 were treated with a saturated vapor of oxalyl chloride in the same way as in Example 6 to form a fibers (II) similar to the fibers (II) obtained in Example 17. The fibers (II) had properties equivalent to those of the fibers (II) obtained in Example 17.

Claims: A process for producing a polymer comprising parabanic acid ring units, which comprises reacting a polycarbodiimide polymer with oxalyl chloride and then treating the reaction product with water, thereby converting at least 50 % of the carbodiimide linkages into parabanic acid ring units. A process according to claim 1 in which the polycarbodiimide polymer is a homopolymer or a copolymer comprising at least one type of recurring unit represented by the following formula -R-N=C=N- wherein R represents an aromatic diisocyanate residue. A process according to claim 1 or 2 in which the polycarbodiimide polymer in the form of a solid is immersed in oxalyl chloride or a solution thereof, or is contacted with oxalyl chloride vapor. A process according to claim 3 in which the polycarbodiimide polymer is treated with a solvent for it prior to the reaction. A process according to claim 1 or 2 in which the polycarbodiimide polymer in the form of a solution is reacted with oxalyl chloride. A process according to any one of the preceding claims in which the reaction of the polycarbodiimide polymer with oxalyl chloride is carried out at a temperature of from ambient temperature to 100°C. A process according to claim 6 in which the temperature is from ambient temperature to 50°C. A process according to any one of the preceding claims in which the treatment of the reaction product with water is carried out at a temperature of from ambient temperature to 100°C. A process according to claim 8 in which the treatment with water is carried out at ambient temperature. A process according to any one of the preceding claims in which more than 90% of the carbodiimide linkages in the polycarbodiimide polymer are converted to parabanic acid ring units. A process according to any one of the preceding claims which further comprises thermosetting the polymer comprising parabanic acid ring units. A polymer comprising parabanic acid ring units and carbodiimide units, which polymer is obtainable from a process which comprises reacting a polycarbodiimide polymer with oxalyl chloride and then treating the reaction product with water, thereby converting at least 50% of the carbodiimide linkages into parabanic acid ring units. A polymer according to claim 12 obtainable from a said process in which the polycarbodiimide polymer is a homopolymer or copolymer comprising at least one type of recurring unit of the formula -R-N=C=N- (I) wherein R is an aromatic diisocyanate residue. A polymer obtainable by thermosetting a polymer as claimed in claim 12 or 13.

Inventors: AMANO SATOSHI, IMASHIRO YASUO, AMANO, SATOSHI, IMASHIRO, YASUO
Applicants: NISSHIN SPINNING, NISSHINBO INDUSTRIES, INC.
Application year: 1989
Main classification: C08G73
IPC codes: C08G73, C08G18