Process for producing aromatic polyimides

Abstract

The invention relates to a process for producing aromatic polyimides, comprising the following steps: (a) preparation of one or more solid salt(s) by reacting one or more aromatic tetracarboxylic acid(s) and one or more diamine(s) according to a mole ratio ranging from 0.95 to 1.05; (b) drying of the solid salt(s), (c) addition, to the dry salt resulting from step (b), of one or more compound(s) (C) comprising one or more group(s) chosen from a carboxylic acid group, an anhydride group, an ester group and an acyl chloride group; (d) solid-state polymerization of said solid salt(s) in the presence of the compound(s) (C).

Claims

1. A process for manufacturing aromatic polyimides, characterized in that it comprises the following steps: (a) preparing one or more solid salts by reacting, one or more aromatic tetracarboxylic acids and one or more diamines in a mole ratio ranging from 0.95 to 1.05; (b) drying the solid salt(s); (c) preparing a polymerization reaction by dry mixing the dry salt derived from step (b) with one or more compounds (C) in a dry state, selected from pyromellitic acid (PMA) and phthalic acid (PHTA), and mixtures thereof; and (d) solid-state polymerization of said solid salt(s) in the presence of the one or more compound(s) (C).

2. The process as claimed in claim 1, characterized in that the solid salt(s) are prepared by reacting one or more aromatic tetracarboxylic acids and one or more diamines in a mole ratio ranging from 0.99 to 1.01.

3. The process as claimed in claim 1, characterized in that the solid salt(s) are prepared by reacting in stoichiometric amount one or more aromatic tetracarboxylic acids and one or more diamines.

4. The process as claimed in claim 1, characterized in that said aromatic tetracarboxylic acids or dianhydrides used in step (a) are chosen from pyromellitic acid, 3,3,4,4-biphenyltetracarboxylic acid, 2,3,3,4-biphenyltetracarboxylic acid, 2,2,3,3-biphenyltetracarboxylic acid, 3,3,4,4-benzophenonetetracarboxylic acid, 2,2,3,3-benzophenonetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 2,3,5,6-pyridinetetracarboxylic acid, 3,4,9,10-perylenetetracarboxylic acid, 3,3,4,4-tetraphenylsilanetetracarboxylic acid, and 2,2-bis(3,4-bicarboxyphenyl) hexafluoropropanetetracarboxylic acid.

5. The process as claimed in claim 1, characterized in that the diamines are molecules of formula H.sub.2NRNH.sub.2 with a linear or branched, saturated or unsaturated aliphatic, cycloaliphatic or aromatic divalent hydrocarbon-based radical R, optionally comprising one or more heteroatoms.

6. The process as claimed in claim 5, characterized in that the radical R comprises from 2 to 50 carbon atoms, and optionally one or more heteroatoms.

7. The process as claimed in claim 1, characterized in that the diamines are aliphatic diamines selected from 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, hexamethylenediamine, 3-methylhexamethylenediamine, 2,5-dimethylhexamethylenediamine, 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 1,7-diaminoheptane, 1,8-diaminooctane, 2,2,7,7-tetramethyloctamethylenediamine, 1,9-diaminononane, 5-methyl-1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, and 1,14-diaminotetradecane.

8. The process as claimed in claim 1, characterized in that the diamine(s) are chosen from cycloaliphatic diamines, and preferably from isophorone diamine, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, diaminodicyclohexylmethane, 1,3-bis(aminomethyl)cyclohexane, 4,4-methylenebis(cyclohexylamine) and 4,4-methylenebis(2-methylcyclohexylamine).

9. The process as claimed in claim 1, characterized in that the diamine(s) are aromatic diamines selected from m-phenylenediamine, p-phenylenediamine, 3,4-diaminodiphenyl ether, 4,4-diaminodiphenyl ether, m-xylylenediamine and p-xylylenediamine.

10. The process as claimed in claim 1, characterized in that the amount of compound (C) introduced into step (c) is greater than 0.5% as number of moles relative to the total number of moles of aromatic tetracarboxylic acid and of diamine used in step (a).

11. The process as claimed in claim 1, characterized in that, during step (d), the polymerization is performed at a temperature T which obeys the following relationship: Tf of the salt from step (a)>T>Tg of the polyimide to be obtained.

12. The process as claimed in claim 1, characterized in that, during step (d), the polymerization is performed at an absolute pressure ranging from 0.005 to 1 MPa.

13. The process as claimed in claim 1, characterized in that, during step (d), the polymerization is performed at a temperature ranging from 50 C. to 250 C.

14. The process as claimed in claim 1, characterized in that the number-average molar mass M.sub.n of the polyimide(s) obtained in step (d) ranges from 500 to 50 000 g/mol.

15. The process as claimed in claim 11, wherein the manufactured aromatic polyimide has a Tg of less than 150 C.

Description

EXAMPLES

(1) Measuring Standards

(2) The melting points (Tf) and the crystallization on cooling points (Tc) of the polyimides are determined by differential scanning calorimetry (DSC), using a TA-Instruments Q20 machine, at a rate of 10 C./min. The Tf and Tc values for the polyimides are determined at the top of the melting and crystallization peaks. The glass transition temperature (Tg) is determined on the same machine at a rate of 40 C./min (when possible, it is determined at 10 C./min and specified in the examples).

(3) For the determination of the melting point of the salt, the end temperature of the endotherm measured by heating the salt at 10 C./min is considered.

(4) The reduced solution viscosity (red) of the polyimides is measured by capillary viscometry using an Ubbelohde viscometer 0.4 mm in diameter in a bath thermostatically maintained at 25 C. The solution of polymer for the analysis is at 5 g/L with a phenol-ortho-dichlorobenzene mixture (50/50 by mass) as solvent. The flow time is measured three times per sample.

(5) The stoichiometry (S) of the dry salt is determined by pH-metric titration using a Mettler-Toledo T50 machine. The titration is performed on a volume of 40 mL of water containing about 0.5 g of dry salt to which are added 10 mL of sodium hydroxide at a concentration of 1 mol/L. The titrating solution used is a hydrochloric acid solution at 1 mol/L. Titration of the sodium hydroxide residue characterized by the first equivalent volume (V1) affords access to the amount of pyromellitic acid (PMA) by back-titration. The differences of the equivalent volumes (V2V1) makes it possible to measure the amount of Jeffamine 150 (J150) by direct titration. The titration is performed on three samples. The stoichiometry S of the salt is thus defined by the mole ratio between the number of moles of tetra-acid and the number of moles of diamine. After addition of the acid chain limiter, a new stoichiometric ratio, S, is defined such that S is equal to the mole ratio between the sum of the numbers of moles of tetra-acid and of acid chain limiter, and the number of moles of diamine. The accuracy of the measurement on the stoichiometric ratios is +0.006. When no chain limiter is added, SS.

Example 1: Preparation of a Salt J150PMA Synthesized in Pure Ethanol

(6) (a) Preparation of the Salt

(7) A 1 L reactor is charged with 85.59 g (0.33 mol) of 96% pyromellitic acid (PMA) (Sigma-Aldrich) and 800 mL of pure ethanol. The reaction medium is stirred at room temperature while flushing gently with nitrogen. 50.82 g (0.34 mol) of 97% Jeffamine 150 (J150) (Huntsman) are dissolved in 200 mL of pure ethanol at room temperature. This solution is then placed in a dropping funnel connected to the 1 L reactor and is added dropwise over 90 minutes to the ethanolic solution of pyromellitic acid. Contact between the diamine and the pyromellitic acid brings about the formation of a salt, which precipitates immediately under vigorous stirring. The reaction medium is maintained under vigorous stirring for 2 hours at room temperature and under nitrogen.

(8) (b) Drying of the Salt Obtained

(9) The salt powder is recovered by vacuum filtration on a sinter and then disintegrated and dried under vacuum at 80 C. overnight. The mass yield is 97.8%. The powder is fine and white. The stoichiometric ratio S of the salt thus obtained is measured via the pH-metric method described above, at 1.012.

Example 1A (Comparative): Preparation of a Polyimide PI J150PMA without Addition of Chain Limiter

(10) (c) Milling of the Dry Solid Salt Obtained on Conclusion of Step (b) of Example 1

(11) A mass of 8.9 g of dry salt J150PMA obtained on conclusion of step (b) of example 1 is milled finely in a mortar without addition of chain limiter.

(12) (d) Solid-State Polymerization of the Dry Solid Salt in the Absence of the Chain Limiter

(13) A mass of 8.9 g of the salt obtained on conclusion of step (c) is placed in a glass tube reactor with mechanical stirring and inertizing with nitrogen. The pressure is equal to atmospheric pressure. The device is heated at 220 C. with stirring for 3 hours. The PI powder J150PMA obtained is white, and perfectly dry. The melting point measured by DSC is 301 C., its crystallization point is measured at 273 C., its glass transition temperature, determined at 10 C./min, is evaluated at 113 C. and its reduced viscosity is 101.9 mL/g.

Example 1B (Invention): Preparation of a Polyimide PI J150PMA with Addition of Chain Limiter (Pyromellitic Acid, PMA) Such that S=1.050

(14) (c) Addition of a Chain Limiter to the Dry Solid Salt Obtained on Conclusion of Step (b) of Example 1

(15) A mass of 0.25 g of pyromellitic acid (PMA) is added to 10.001 g of dry salt J150PMA obtained on conclusion of step (b) of example 1. The mixture of the two powders is finely milled in a mortar. The theoretical stoichiometry S of the salt thus prepared is equal to 1.050.

(16) (d) Solid-State Polymerization of the Dry Solid Salt Obtained on Conclusion of Step (c)

(17) The salt obtained on conclusion of step (c) is placed in a glass tube reactor with mechanical stirring and inertizing with nitrogen. The pressure is equal to atmospheric pressure. The device is heated at 220 C. with stirring for 3 hours. The PI powder J150PMA obtained is white, and perfectly dry. The melting point measured by DSC is 299 C., its crystallization point is measured at 270 C., its glass transition temperature, determined at 10 C./min, is evaluated at 110 C. and its reduced viscosity is 49.1 mL/g.

Example 1C (Invention): Preparation of a Polyimide PI J150PMA with Addition of Chain Limiter (Phthalic Acid, PHTA) Such that S=1.049

(18) (c) Addition of a Chain Limiter to the Dry Solid Salt Obtained on Conclusion of Step (b) of Example 1

(19) A mass of 0.154 g of 99% phthalic acid (PHTA) (Aldrich) is added to 10.005 g of dry salt J150PMA obtained on conclusion of step (b) of example 1. The mixture of the two powders is finely milled in a mortar. The theoretical stoichiometry S of the salt thus prepared is equal to 1.049.

(20) (d) Solid-State Polymerization of the Dry Solid Salt Obtained on Conclusion of Step (c)

(21) The salt obtained on conclusion of step (c) is placed in a glass tube reactor with mechanical stirring and inertizing with nitrogen. The pressure is equal to atmospheric pressure. The device is heated at 220 C. with stirring for 3 hours. The PI powder J150PMA obtained is white, and perfectly dry. The melting point measured by DSC is 298 C., its crystallization point is measured at 262 C., its glass transition temperature, determined at 10 C./min, is evaluated at 96 C. and its reduced viscosity is 48.0 mL/g.

Example 2 (Comparative): Preparation of a Polyimide PI J150PMA by Solid-State Polymerization of a Salt Such that S=1.038, without Addition of Chain Limiter

(22) (a) Preparation of the Salt

(23) A 1 L reactor is charged with 27.04 g (0.107 mol) of 96% pyromellitic acid (PMA) (Sigma-Aldrich) and 800 mL of pure ethanol. The reaction medium is stirred at room temperature while flushing gently with nitrogen. 15.43 g (0.104 mol) of 97% Jeffamine 150 (J150) (Huntsman) are dissolved in 200 mL of pure ethanol at room temperature. This solution is then placed in a dropping funnel connected to the 1 L reactor and is added dropwise over 90 minutes to the ethanolic solution of pyromellitic acid. Contact between the diamine and the pyromellitic acid brings about the formation of a salt, which precipitates immediately under vigorous stirring. The reaction medium is maintained under vigorous stirring for 2 hours at room temperature and under nitrogen.

(24) (b) Drying of the Salt Obtained

(25) The salt powder is recovered by evaporating off the solvent using a rotary evaporator at 79 C. while flushing with nitrogen at atmospheric pressure. The mass of dry salt recovered is 40.6 g, i.e., a mass yield of 97.2%. The powder is fine and white. The stoichiometric ratio S of the salt thus obtained is measured via the pH-metric method described above, at 1.038.

(26) (c) Milling of the Dry Solid Salt

(27) A mass of 10 g of dry salt J150PMA obtained on conclusion of step (b) is milled finely in a mortar without addition of chain limiter.

(28) (d) Solid-State Polymerization of the Dry Solid Salt Obtained on Conclusion of Step (c)

(29) The salt obtained on conclusion of step (c) is placed in a glass tube reactor with mechanical stirring and inertizing with nitrogen. The pressure is equal to atmospheric pressure. The device is heated at 220 C. with stirring for 3 hours. The PI powder J150PMA obtained is white, and perfectly dry. The melting point measured by DSC is 300 C., its crystallization point is measured at 262 C., its glass transition temperature, determined at 10 C./min, is evaluated at 111 C. and its reduced viscosity is 60.1 mL/g.

Example 3 (Comparative): Preparation of a Polyimide PI J150PMA with Addition of Chain Limiter (Octylamine, MA8) Such that S=0.916

(30) (a) Preparation of the Salt

(31) A 1 L reactor is charged with 65.02 g (0.256 mol) of 96% pyromellitic acid (PMA) (Sigma-Aldrich) and 800 mL of pure ethanol. The reaction medium is stirred at room temperature while flushing gently with nitrogen. 38.45 g (0.252 mol) of 97% Jeffamine 150 (J150) (Huntsman) are dissolved in 200 mL of pure ethanol at room temperature. This solution is then placed in a dropping funnel connected to the 1 L reactor and is added dropwise over 90 minutes to the ethanolic solution of pyromellitic acid. Contact between the diamine and the pyromellitic acid brings about the formation of a salt, which precipitates immediately under vigorous stirring. The reaction medium is maintained under vigorous stirring for 2 hours at room temperature and under nitrogen.

(32) (b) Washing and Drying of the Salt Obtained

(33) The salt powder is recovered by vacuum filtration on a sinter and then washed with refluxing ethanol (1.2 L) with stirring for 3 hours. The washed salt powder is filtered again by vacuum on a sinter and then disintegrated and dried under vacuum at 80 C. overnight. The mass yield is 97%. The powder is fine and white. The stoichiometric ratio S of the salt thus obtained is measured via the pH-metric method described above, at 1.008.

(34) (c) Addition of the Chain Limiter to the Dry Solid Salt Obtained on Conclusion of Step (b)

(35) A mass of 0.413 g of 99% octylamine (MA8) (Aldrich) is added to 12 g of dry salt J150PMA obtained on conclusion of step (b). The mixture of the salt powder and of octylamine is finely milled in a mortar. The stoichiometry S of the salt thus prepared is equal to 0.916.

(36) (d) Solid-State Polymerization of the Dry Solid Salt Obtained on Conclusion of Step (c)

(37) The salt obtained on conclusion of step (c) is placed in a glass tube reactor with mechanical stirring and inertizing with nitrogen. The pressure is equal to atmospheric pressure. The device is heated at 220 C. with stirring for 3 hours. The PI powder J150PMA obtained is white, and perfectly dry. The melting point measured by DSC is 300 C., its crystallization point is measured at 268 C., its glass transition temperature, determined at 10 C./min, is evaluated at 108 C. and its reduced viscosity is 170.8 mL/g.

(38) All the results obtained in the above examples are collated in table 1 below:

(39) TABLE-US-00001 TABLE 1 Chain limiter Reduced introduced into viscosity Tf Tc Tg Example step (c) S (mL/g) ( C.) ( C.) ( C.) 1A 1.012 101.9 301 273 113 1B PMA 1.050 49.1 299 270 110 1C PHTA 1.049 48 298 262 96 2 1.038 60.1 300 262 111 3 MA8 0.916 170.8 300 268 108

(40) Example 3 shows that the process used for the manufacture of polyimides, using octylamine (a monoamine) as chain limiter, is unsatisfactory. Specifically, the polyimide obtained has a reduced viscosity of 170.8 mL/g, which is well above the value of 101.9 mL/g obtained for the polyimide manufactured according to a process disclosed in comparative example 1A. This example 3 proves the fact that octylamine did not act as chain limiter as expected.

(41) Examples 1B and 1C firstly demonstrate the efficiency of the process according to the invention since a polyimide with a satisfactory viscosity was obtained in each case.

(42) They also demonstrate the fact that both pyromellitic acid (example 1B) and phthalic acid (example 1C) introduced, respectively, during step (c) of the process of the invention, afforded particularly satisfactory control of the chain length of the polyimide obtained. Specifically, the polyimides obtained have, respectively, a reduced viscosity of 49.1 mL/g (example 1B) and of 48 mL/g (example 1C). These values are very much lower than the value of 101.9 mL/g obtained for the polyimide manufactured in the context of example 1A, and lower than the value of 60.1 mL/g obtained in the context of example 2.