Patent Application
20240228704
The present application claims priority under 35 USC § 119 to European application EP 22214870.2, filed on Dec. 20, 2022, the content of which is incorporated herein by reference in its entirety.
The present invention relates to novel, melt-processable polyimides that show a high glass transition temperature, a process for preparing these polyimides and also the use of the new polyimides.
High performance and high-temperature polymers exhibit superior thermal stability, heat resistance and chemical resistance compared to commodity polymers. These high-performance polymers additionally demonstrate good mechanical properties, with increased stability under high load and stress and dimensional stability. Being an important representative of the high performance and high-temperature polymers, polyimides show remarkable properties. They offer high-temperature stability with decomposition temperatures over 450° C. and a high glass transition temperature (Tg) in the range of 200° C. and 300° C. some even exceeding 400° C. A major reason for the thermal stability is the high degree of aromaticity. High aromaticity results in increased stiffness of the polymer chain leading to an amorphous structure. The increased chain rigidity makes polyimides often insoluble and infusible, which causes difficulties in melt processing. This is because by processing from the melt the thermal stability limit of the polyimide may be reached, and polymer degradation may take place during processing. For this reason, polyimides are often processed from their precursor polyamic acid by casting followed by imidization of the polyamic acid, e.g. by heat treatment, to obtain the polyimide. Another method applied for processing of polyimides is the hot press technique where the polymer powder is placed in a mould undergoing sintering and pressure treatments. The obtained polyimide shape can be further processed by drilling or cutting into the desired shape. A further processing method for polyimides would be by ram extrusion which yields a rod-shaped material. The processing methods of polyimides available today are complex and lack efficiency, thus, processing of polyimides by the use of conventional moulding machines is desirable and attempts have been made to develop melt processable polyimides.
Mittal, K. L., “Polyimides Synthesis, Characterization and Applications”, 1st ed .; Springer, Boston, MA, 1984. https://doi.org/https://doi.org/10.1007/978-1-4615-7637-2 and Okuyama, K. et al., “X-Ray Structure Analysis of a Thermoplastic Polyimide”, Macromolecules 1992, 25 (26), 7261-7267. https://doi.org/10.1021/ma00052a030 disclose concepts to introduce flexible units like ether groups in polyimide polymers to enhance the chain movement. Based on this concept, Tamai, S. et al., “Melt Processible Polyimides and Their Chemical Structures”, Polymer (Guildf), 1996, 37 (16), 3683-3692, prepared various diamines with different amount of other groups and synthesized polyimides with the dianhydride ODPA as shown in Table 1. As can be observed from Table 1, most polyimides comprising ether functionalities exhibit insufficient thermal resistance. Having a Tg<270° C. these polyimides cannot be used in high temperature applications. Polyimide a) of Table 1 does not comprise ether groups and is not melt processable.
Another concept applied to develop melt processable polyimides was the introduction of crystallinity to polyimides. This should improve their solvent resistance, increase the modulus and should keep their mechanical properties almost unchanged above their Tg. Some examples of commercially available semicrystalline polyimides and their thermal properties are depicted in Table 2. All polyimides shown in Table 2 have in common the presence of arylene ether and arylene keto moieties and meta catenations.
The polyimides shown in Table 2 are melt-processable. LaRC-TPI is melting but exhibits a high melt viscosity which challenges processing. This problem was solved by processing LaRC-TPI as copoly(imide/amic acid) material reducing the melt viscosity to towards processability. All polyimides shown in Table 2, however, exhibit insufficient thermal resistance. Having a Tg≤250° C. they cannot be used in high temperature applications.
Another class polyimide materials used to gain melt processability are polyetherimides. A commercially available polyetherimide is ULTEM depicted in Table 3. ULTEM is amorphous structured and exhibits a Tg at 217° C. This polymer is melt-processable by injection moulding extrusion and blow moulding. The melt processability is attributed to the presence of the flexible ether groups but also to the methyl groups of the bisphenol. However the methyl groups decrease the thermo-oxidative stability of the polymer compared to fully aromatic polymers.
US 2008/0044684 discloses articles comprising a polyimide solvent cast film having a low coefficient of thermal expansion. According to US 2008/0044684 the polyimides exhibit only a short survivability at temperatures up to 260° C. No information regarding melt viscosity of the polyimides is provided.
US 2006/281840 A1 discloses a method of stabilization of polyetherimide sulfones being melt processable at temperatures of more than 250° C. but does not disclose any polyimides being melt processable at temperatures of more than 290° C.
As shown above, even though many approaches have been tested, there is still a high demand in the market for melt processable polyimides with high thermal stability, in particular for polyimides that can be processed via injection molding and having a glass transition temperature Tg≥290° C.
Subject of the present invention, thus, was to provide new polyimides that are melt processable polyimides and show high thermal stability as well as to provide a process for their manufacturing.
Another preferred subject of the present invention was to provide polyimides and a process for their manufacture that can be processed via injection molding and having a glass transition temperature Tg≥290° C.
Another preferred subject of the present invention was to provide polyimides and a process for their manufacture that show high thermal stability and are melt processable without changing their color.
Another preferred subject of the present invention was to provide polyimides and a process for their manufacture that are melt processable and having a Tg≥290° C. which can be adjusted over a broad range to provide high flexibility for intended use.
Another preferred subject of the present invention was to provide polyimides and a process for their manufacture that are melt processable under high processing temperatures, preferably up to 420° C., more preferred up to 390 to 400° C. without relevant degradation of the polymer chain.
Further problems not explicitly mentioned before can be derived from the overall content of the subsequent description, examples, and claims.
The inventors surprisingly found out, that by grouping specific flexible and stiff units in polyimide polymers it was possible to obtain polyimides having a Tg≥290° C. which are melt processable, in particular injection moldable. As stiff unit a unit having sulphone functionality was found to be best suitable to solve the problems of the invention. Inventors further found out that the structure of the unit having sulphone functionality having an impact on the thermal stability of the polyimides. While the problems of the invention have been solved by use of 4,4′-diaminodiphenylsulphone, use of 3,3′-diaminodiphenylsulphone lead to polyimides with Tg≤290° C. Also use of diamines with keto functionality as stiff unit, like 3,3′-Diaminobenzophenone and 4,4′-Diaminobenzophenone did result in polyimides with Tg≤290° C.
As diamines several ether-bridged aromatic diamines as claimed in claim 1 can be used as flexible units in the polyimides of the invention to solve the problems of the invention. The same is true with regard to the dianhydride units as claimed in claim 1. As will be shown in the examples below, variation of the composition of the polyimide by choosing the dianhydride unit and the flexible unit as well as by changing the molecular composition of the polyimides the thermal properties of the polyimides, in particular the Tg can be adjusted as required by the desired application.
It has further been found that thermal post-treatment of the inventive polyimides can effectively be used for further purification of the polyimides in needed. This provides another degree of flexibility with regard to the fields applications of the inventive polyimides.
TGA measurements of the inventive polyimides showed that no degradation of the polymer chain even at 450° C. was observed. Thus, the inventive polyimides can by used even in high temperature processing processes.
Another degree of flexibility for the inventive polyimides is the use or non-use of end-cappers, which bond to terminal amino groups of the polymer chain. These end-cappers have an influence on the melt viscosity of the inventive polyimides. While polyimides without end-capper show increased melt viscosity in a second melt cycle compared to the first melt cycle, polyimides with end-cappers show constant melt viscosities in melted several times. This provides another degree of flexibility for the inventive polyimides.
Further benefits will be apparent from the subsequent description, examples, claims and figures.
Before describing the invention in more details, some important terms are defined as follows:
The verb “to comprise” as is used in the description, examples and the claims and its conjugation is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. “Comprising” includes “consisting of” meaning that items following the word “comprising”, are included without any additional, not specifically mentioned items, as preferred embodiment.
Reference to an element be the indefinite article “a” or “an” does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there is one and only one of the elements. The indefinite article “a” or “an” thus usually means “one or more”.
Subject of the present invention are polyimides comprising building units (A) and (B) having the following structures (Ia) and (Ib)
As will be demonstrated in the examples below the molar ratio of the stiff monomer R2 to the flexible monomer R4 has strong impact on the glass transition temperature of the polyimides. If the content of the stiff polymer R2 is below 75% in combination with R4a or R4b or R4c respectively below 80 mol % in combination with R4d, the Tg value of the polyimides decreases below 290° C. On the other hand, if no flexible monomer is present the resulting polyimides lack melt processability. Meaning the molar ratio of R2 to the sum of all R4 units can be varied in a range of from
Appropriate combination will be chosen by a man skilled in the art depending on the desired glass transition temperature of the resulting polyimide. Preferred molar ratios of R2 to the sum of all R4 units are in a range of from,
If R4 is R4c further preferred ranges for the molar ratio of R2 to R4c are 0.99:0.01 to 0.81:0.19, preferably of from 0.98:0.02 to 0.81:0.19 and more preferred of from 0.95:0.05 to 0.82:0.18 if R4 is R4c.
Within the group of flexible monomer units R4a to R4d it has been found that polyimides comprising R4c and/or R4d show best combinations of thermal resistance and melt processability. It is thus preferred, if R4 comprises R4c and/or R4d.
Selection of monomer units R1 has an impact on the glass transition temperature of the inventive polyimides, too. Analogue to the monomer units R2 and R4 the less flexible monomer unit R1 with X=X1 results in higher glass transition temperatures compared to more flexible monomer unit R1 with X=X2. It is preferred, if X=comprises X1 or X2 or a mixture of X1 and X2, preferably X comprises X2.
In order to keep the complexity of the reaction and the number of monomers to be handled low, R1 and R3 are preferably identical. However, it is also possible to select R1 and R3 differently. Basically, the same principles apply to the selection of R3 as to R1. Selection of monomer units R3 has an impact on the glass transition temperature of the inventive polyimides, too. Analogue to the monomer units R2 and R4 the less flexible monomer unit R3 with Y=Y1 results in higher glass transition temperatures compared to more flexible monomer unit R3 with Y=Y2. It is preferred, if Y=comprises Y1 or Y2 or a mixture of Y1 and Y2, preferably Y comprises Y2.
R1 may comprise further monomers selected from the group consisting of 3,3′,4,4′-biphenyl-tetracarboxylic acid dianhydride, 2,3,3′,4′-biphenyl-tetracarboxylic acid dianhydride, 2,2′,3,3′-biphenyl-tetracarboxylic acid dianhydride, pyromellitic dianhydride, 3,4′-oxxydiphthalic anhydride and mixtures thereof in sum in an amount of from 0.01 to 50 mol %, preferably of from 0.1 to 30 mol %, more preferred of from 0.01 to 30 mol %, even more preferred of from 0.5 to 20 mol %, particular preferred of from 0.5 to 10 mol % and most preferred of from 0.5 to 5 mol %. Preferably R1 comprises in total to an extent ≥70 mol %, more preferred to an extent ≥80 mol %, yet more preferred to an extent from 90 to 100 mol %, yet still more preferably to an extent from 95 to 100 mol % and most preferred to a 100 mol % extent of
R3 may comprise further monomers selected from the group consisting of 3,3′,4,4′-biphenyl-tetracarboxylic acid dianhydride, 2,3,3′,4′-biphenyl-tetracarboxylic acid dianhydride, 2,2′,3,3′-biphenyl-tetracarboxylic acid dianhydride, pyromellitic dianhydride, 3,4′-oxxydiphthalic anhydride and mixtures thereof in sum in an amount of from 0.01 to 50 mol %, preferably of from 0.1 to 30 mol %, more preferred of from 0.01 to 30 mol %, even more preferred of from 0.5 to 20 mol %, particular preferred of from 0.5 to 10 mol % and most preferred of from 0.5 to 5 mol %. Preferably R3 comprises in total to an extent ≥70 mol %, more preferred to an extent ≥80 mol %, yet more preferred to an extent from 90 to 100 mol %, yet still more preferred to an extent from 95 to 100 mol % and most preferred to a 100 mol % extent of
with Y being selected from the group consisting of Y1, Y2, Y3, Y4 and mixtures thereof, preferably Y being selected from Y1, Y2 and mixtures thereof, more preferred Y being Y2.
Preferably R4 comprises in total to an extent ≥65 mol %, preferably to an extent ≥80 mol %, more preferably to an extent from 90 to 100 mol %, yet more preferably to an extent from 95 to 100 mol % and most preferably to a 100 mol % extent of R4a, R4b, R4c, R4d and mixtures thereof, preferably R4c, R4d and mixtures thereof, more preferred of R4c. The remaining R4 up to 100 mol % are preferably divalent spacers derived from diamines, preferably the spacers different from R4a, R4b, R4c and R4d comprise aromatic units, more preferred are selected from the group consisting of R4e, R4f, R4g and R4h, with the formula
The polyimide polymers of the invention may be random copolymers, meaning all monomers are mixed before polymerization is started and polymer chains without predefined monomer order are obtained. In this case m and n are preferably in the following ranges
It is, however, also possible to prepare block-co-polymer, wherein the building units (A) and (B) each are building blocks (A) and (B) and wherein the block lengths n and m of blocks (A) and (B) are each from 1 to 1000, preferably from 1 to 500, more preferably from 1 to 200, yet more preferably from 5 to 150, yet still more preferably from 10 to 100, yet still even more preferably from 10 to 50 and most preferably from 10 to 40.
Best mechanical properties of the inventive polyimides have been found if
It has been found that processability decreases if molecular weight is too high. If the molecular mass is too low brittleness of the inventive polyimides might be too high. Further benefits in terms of toughness, tensile strength and flexural strength have been found if the molecular mass is in the ranges defined above.
Most homogeneous properties of the inventive polymers have been found if polydispersity index D is of from 1 to 10, preferably 1.1 to 5, more preferably 1.2 to 4, yet more preferably 1.3 to 3 and most preferably 1.4 to 2.4. If the molecular mass distribution is smaller, a more homogeneous melt behavior was observed.
It has been found that inventive polymer produced from the building units (A) and (B) are melt processable, in particular are injection moldable, and have a Tg>290° C. It has further been found that the melt viscosity of polymers comprising building units (A) and (B) but not end-cappers increases if the polymers are repeatedly melted or if the polymers are kept in melt over a longer period of time. Without being bond to any theory this behavior might be a result of the presence of active end groups in the polymer. Active end groups may be free amine moieties that were not reacted during polymerization or imidization. A temperature increase during melt processing induces a reaction of these end groups which seems to cause an increase of the viscosity. The more often the polymers are melted, the higher the melt viscosity is until all reactive groups have reacted.
To allow repeated heating of the inventive polymers or if heating over a very long period of time is needed, inventors have found out that increase of the melt viscosity of the inventive polymers can be avoided if the active end groups are capped with end-cappers. The end cappers are preferably mono-functional anhydrides that are added during or after polymerization to react with free amino groups of the polymer, i.e. free amine moieties that were not reacted during the PAA formation and cap these groups so that they are no longer reactive if the polymer is heat treated. The inventive polyimides thus comprise end-capping units bound to free amino group of the polymer, preferred end-capping units are mono-functional anhydride monomers without crosslinking functionality, more preferred mono-functional anhydride monomers selected from the group consisting of succinic anhydride, phthalic anhydride and its derivatives according to the following structure
As mentioned before the end-capping monomers, herein also named end-capping units or end-cappers, are preferably added during polymer synthesis. They can be added before or after addition of the dianhydride(s). More preferred the end-capping monomers are added as long as the polymer is in solution, i.e. before imidization takes place. If the end-cappers are added during polymer synthesis, it was observed that it is preferred that the amine and anhydride functionalities are stochiometrically balanced after end-capper addition. If addition of the end cappers leads to an excess of anhydride moieties, degradation of the polymer by disturbing the reaction equilibrium might be caused. This might result in a decrease of the molecular mass and the thermal stability. It is thus, preferred if the end-capper is comprised in an amount of ≤0.02 mol %, preferably 0.001 to 0.015 mol % and more preferred 0.002 to 0.01 mol %. Most preferred the end-capping units is present in an amount as defined before and simultaneously the sum of all anhydride functionalities is stochiometrically balanced with the sum of all amine functionalities. Stochiometrically balanced means a mole ratio of the sum of all anhydride functionalities to the sum of all amine functionalities is of from 0.9:1 to 1 to 0.9, preferably 0.95:1 to 1 to 0.95, more preferred 0.98:1 to 1 to 0.98 and most preferred 1 to 1.
The polyimides of the invention preferably comprise one or more additives selected from the group consisting of lubricants, preferably lithium stearate, graphite, metal sulfides, and polymer stabilizers, such as sterically hindered phenols or sterically hindered amines or phosphite esters.
The polyimides of the invention may be produced by a process comprising the steps
If R4 is R4c further preferred molar ratios of R2 to R4c are 0.99:0.01 to 0.81:0.19, preferably of from 0.98:0.02 to 0.81:0.19 and more preferred of from 0.95:0.05 to 0.82:0.18 if R4 is R4c.
In step a. it is preferred
It is preferred to carry out step a under water free conditions and/or inert atmosphere because water may cause an imbalance in the reaction stoichiometry, which may lead to a low molecular weight. Also the dianhydride is more likely to react with water forming orthodicarboxylic acid, which is not as reactive as the anhydride group.
To reduce potential risk of side reactions, it is preferred to conduct step a by adding the dianhydride monomers to the amine monomers as described before, even more preferred the dianhydride is added step by step during polymer growth. This leads to high molecular masses.
Preferably the sum of all anhydride moieties added in step a. is stoichiometric balanced to the sum of to the amine moieties added in step a. This allows to obtain inventive polyimides with particularly high molecular mass. Stoichiometrically balanced means a mole ratio of the sum of all anhydride functionalities to the sum of all amine functionalities is of from 0.9:1 to 1 to 0.9, preferably 0.95:1 to 1 to 0.95, more preferred 0.98:1 to 1 to 0.98 and most preferred 1 to 1.
All known imidization methods can be used in step b. Preferably imidization can be affected thermally or chemically or by precipitation imidization or by combination of these methods, more preferably by heating the polyamic acid followed by colling to causes precipitation.
If step b. is carried out by chemical imidization it is preferred to affect the imidization by adding a base and a dehydrating agent to the polyamic acid, wherein the base is more preferably admixed in just a catalytic amount. It is further preferred to control the solid content of the polyamic acid solution to be in a range of from 15 to 30% by weight, more preferred 20 to 27% by weight. Even more preferred the solid content is adjusted before the base and the dehydrating agents are added. It has been found that the polyimide powder particles obtained at higher solid contents are too hard and that larger particles are obtained that melt slower than smaller particles.
For the reasons explained before the process of the invention comprises the step adding an end-capping unit that reacts with free amino group of the polymer, preferably a mono-functional anhydride monomer, more preferred a mono-functional anhydride monomer without crosslinking functionality, even more preferred a mono-functional anhydride monomer selected from the group consisting of succinic anhydride, phthalic anhydride and its derivatives according to the following structure
It is further preferred that the process of the invention comprises an additional step c. isolating the polyimide. To remove impurities from the polyimides, it is preferred that step c. comprises the following steps, precipitating the polyimide and separating the precipitate from the solvent, more preferred followed by washing the precipitate and drying.
It has been found that a small particle size of the polyimide powder is beneficial for melt extrusion application. Smaller particles have a larger surface. A larger surface allows better heat transfer and leads to shorter melt times. It is thus, preferred that the particles having an average particle size of from 10 to 250 microns. It is further preferred to adjust the average particle size by stirring the reaction mixture during precipitation or by applying shear forces during or after precipitation.
For the reasons mentioned before it is also preferred to conduct an additional step d. grinding of the polyimide obtained in step b. or c. Step d. can be carried out as alternative to stirring or the application of shear forces or in addition to said measures.
Inventors found out that inventive polyimides may comprise impurities even if step c. is carried out. Such impurities may cause gas formation during melt processing at higher temperatures because of thermal degradation of these impurities. This effect can be beneficial if melt extruded products with a lower density are to be produced. If, however, the gas formation needs to be avoided or reduced, meaning gas forming impurities need to be removed from the inventive polyimides, this can be done in an additional step e. heating the polyimide to a temperature above its TG. It has been found that impurities can be even better removed if step e. is carried out under reduced pressure.
The inventive polyimide can be used in any typical application for high-temperature resistant polyimides, in particular in melt-extrusion, injection molding, direct forming and hot-compression molding processes, most preferably melt-extrusion and injection molding.
TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) measurements were carried out with a TGA TA instruments Q5000 and a DSC TA instruments Q2000 both equipped with an autosampler. The DSC measurements were carried out under nitrogen.
TG and Tm were measured using DSC TA instruments Q2000 both equipped with an autosampler.
Molar mass is determined by gel permeation chromatography. Calibration is against polystyrene standards. The molar masses reported are thereto formed to be understood as relative molar masses.
The dispersity D of the polymer is the quotient Mw/Mn. The molar masses are relative molar masses based on polystyrene standards.
The degree of polymerization is a purely arithmetic quantity and is obtained from the molar ratio of the monomers used.
The examples which follow serve to provide more particular elucidation and better understanding of the present invention, but do not limit it in any way.
Phthalic anhydride was obtained from TCI
BTDA: Benzophenone-3,3′,4,4′-tetracarboxylic dianhydride was obtained from Jayhawk Fine Chemicals Corporation
ODPA: 4,4′-Oxydiphthalic anhydride was obtained from Jayhawk Fine Chemicals Corporation
6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride was obtained from Daikin Chemicals
4,4′-oxydiphenol (9.30 g, 46.0 mmol) was dissolved in 160 mL DMAc. Then finely grinded, dry K2CO3 (14.11 g, 102.1 mmol) and 160 mL toluene were added. The suspension was stirred under argon at 135° C. for 1.5 h and then the temperature was increased to 175° C. Meanwhile water is collected via a Dean-Stark trap and removed with the toluene from the system. The dark suspension was afterwards cooled to room temperature, 1-fluoro-4-nitrobenzene (16.36 g, 115.9 mmol) was added, and the reaction mixture heated to 160° C. over night. After cooling to room temperature 400 mL water were added and the product was extracted with 400 mL DCM.
The organic phase was washed with water and dried with MgSO4. The solvent was removed, and the product recrystallized in acetone/EtOH (50/50). Drying in vacuum over CaCl2 yielded Bis[4-(4-nitrophenoxy)phenyl] ether (14.91 g, 33.56 mmol, 73%).
1H-NMR (300 MHz, CDCl3) δ/ppm: 8.22 (d, 4H, J=9.3 Hz), 7.10 (s, 8H), 7.04 (d, 4H, J=9.3 Hz). 13C-NMR (75 MHz, CDCl3) δ/ppm: 163.3, 154.5, 150.3, 142.7, 126.1, 122.2, 120.5, 116.9. FT-IR v/cm−1: 3114, 1584, 1484, 1371, 1341, 1259, 1222, 1188, 1162, 1109, 950, 839, 770, 747, 684.
HRMS (ESI, positive): m/z calculated for C24H16N2O7 444.0958, found 445. 1012 [M+H]+
Bis[4-(4-nitrophenoxy)phenyl] ether (9.33, 21.0 mmol) was dissolved in 100 mL dry THF in a hydrogenation bottle. 0.90 g (8.45 mmol) of 10% Pd/C were added and the bottle was placed in a Parr hydrogenator. 0.53 MPa H2 were adjusted, and the reaction was performed over night. Then the mixture was filtered over a celite patch, and the solvent removed. The product was recrystallized in EtOH to yield BDA as a beige solid (6.53 g, 16.99 mmol, 81%)
1H-NMR (300 MHz, CDCl3) δ/ppm: 6.91 (m, 8H), 6.87 (d, 4H, J=8.8 Hz), 6.68 (d, 4H, J=8.8 Hz), 3.56 (s, 4H).
13C-NMR (75 MHz, DMSO-d6) δ/ppm: 154.4, 151.7, 146.1, 145.3, 120.5, 119.6, 118.0, 114.8. FT-IR v/cm−1: 3559, 3385, 3315, 1879, 1615, 1489, 1322, 1275, 1191, 1098, 1009, 938, 825, 800, 747, 699.
HRMS (ESI, positive): m/z calculated for C24H20N2O3 384.1474, found 385. 1550 [M+H]+
4,4′-diiodobiphenyl (7 g, 17.24 mmol), 3-aminphenol (9.03 g, 82.76 mmol), 2-picolinic acid (0.21 g, 1.72 mmol), copper(I) iodide (0.16 g, 0.86 mmol) and potassium phosphate (7.32 g, 34.48 mmol) were weighed under argon in a Schlenk tube. Dry DMSO (43 mL) was added, and the reaction mixture was stirred at 80° C. over night. The product was extracted with EtOAc and washed with water and a K2CO3 solution. The organic phase was washed with water until pH=7 was reached. After drying with MgSO4, the solvent was removed, and the obtained crude product was hot steam extracted with heptane. The precipitates from heptane as white solid, which was isolated by filtration, washed with heptane and dried in vacuum at 70° C. The obtained white solid was additionally purified by column chromatography (EtOAc/heptane).
1H-NMR (300 MHz, DMSO-d6) δ/ppm: 7.63 (d, 4H, J=8.9 Hz), 6.98-7.05 (m, 6H), 6.32-6.36 (m, 2H), 6.16-6.22 (m, 4H).
13C-NMR (75 MHz, DMSO-d6) δ/ppm: 157.5, 156.3, 150.5, 134.4, 130.1, 127.8, 118.9, 109.4, 106.0, 103.9.
FT-IR v/cm−1: 3404, 3311, 3210, 3040, 3011, 1587, 1465, 1327, 1286, 1235, 1166, 1133, 1073, 994, 962, 855, 830, 773, 685.
HRMS (ESI, positive): m/z calculated for C24H20N2O2 368.1525, found 369.1718 [M+H]+
In step a) a polyamic acid was prepared under nitrogen and by using a mechanical stirrer, by dissolving the diamines listed in Tables 6 to 11 were in DMF and adding the dianhydrides and optionally monoanhydrides listed in Tables 6 to 11 to the solution in portions and stirring the reaction mixture over night at room temperature. The monomer amount was adjusted for a 15% solid content.
In step b) imidization was achieved in three different ways, dependent on the diamine monomer used.
For the thermal imidization a small amount of PAA was drop casted on a clean glass substrate and heat treated in an oven under air using the temperature program described in Table 5. The resulting film was removed by immersing the substrate into water.
The imidization reaction takes place in a three-neck round bottom flask which is equipped with mechanical stirrer, a nitrogen inlet and a column, which is packed with glass Raschig Rings. A column head is placed on the top of the column for controlling solvent reflux. 200 mL DMF with 2 g (20.4 mmol) phosphoric acid were heated to reflux until constant temperature was reached. Then the PAA was added dropwise to the solvent mixture. During PAA addition, condensate was collected via the column head in the same rate as the addition of the PAA takes place. After addition was completed, the reaction mixture was refluxed for another 2 h. The resulting precipitate was filtered, washed with water and dried at 160° C. over night.
Acetic anhydride (2.4 equ. of the amount of dianhydride) and pyridine (4.8 eq. of the amount of dianhydride) were added dropwise as a mixture to the PAA. After addition the PAA was stirred under nitrogen over night.
If a precipitate had formed, it was collected via filtration washed with 0.5 L DMF, 3 L water and 0.5 L EtOH. The polymer was dried over night in the vacuumed desiccator over CaCl2, then finely grinded and again dried in vacuum at 150° C. for three days.
If no precipitate was formed over night, the polymer was precipitated in water and finely grinded. The polymer washing and drying was performed as described previously.
The following inventive polyimides (IPI) were prepared (Tms were detected in the first run and Tgs were detected in second run of the DSC measurement):
Polymers were prepared as shown in Example 1 with the modification that all polymers were end-capped with, preferably an amount of 0.01 mol, phthalic anhydride (stochiometrically balanced with the dianhydride moiety), which was added during step a) to cap free amino group at the ends of the polymer chains of the polymer back bone.
The following inventive polyimides (IPI) and comparative, non-inventive polyimides (CPI) were prepared (Tms were detected in the first run and Tgs were detected in second run of the DSC measurement):
The results shown in Tables 7 to 11 show that all inventive polyimides (IPI), having a content of 4,4′DDS of minimum 80 mol % of the amine mix, show high thermal restistance and solve the problem of the invention to provide a Tg of equal than or higher than 290° C. In contrast thereto the comparative polyimides (CPI) show that Tg decreases below 290° C. if the 4,4′DDS content of the amine mix is below 80 mol %. Comparison of inventive examples IPI 6 and IPI 9 shows that use of BTDA instead of ODPA leads to slightly higher Tg and that the selection of the dianhydride component can be used to adapt the Tg. Comparison of examples CPI 9 to 11 with inventive examples IPI 5 to 8 shows that use of an end-capper has minor effect on Tg. Measurement of melt viscosity, however showed that the polyimides without end capper showed a higher viscosity in a second melt cycle compared to the first melt cycle while inventive polyimides with end-capper show consistent melt viscosities even if melted several times.
In a 500 ml flask, 29.796 g/0.12 mol of bis(4-aminophenyl) sulfone (4,4′-DDS) and 8.77 g/0.03 mol of 1,3-bis(4-aminophenoxy)benzene (RODA) were dissolved in 257 g DMF. Then, 0.222 g/0.0015 mol of Phthalic anhydride, 23.033 g/0.0743 mol of 4,4′-oxydiphthalic anhydride (ODPA) and 33.315 g/0,075 mol of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) were stepwise added to the cooled (15° C.) reaction solution.
Preparation of PAA as well as chemical imidization were carried out as described previously.
Table 12 shows that it is possible to use mixed dianhydrides selected from the dianhydrides claimed in claim 1 as starting material.
Table 13 shows that even with increased amounts of endcappers Tg remains above 290° C.
Rheological measurements of the comparative polyimides CPI 9 to 12 show that these polyimides are melt processable. After repeating the measurement in a second melt cycle the polymers show a higher viscosity compared to the viscosity measured in the first melt cycle but the polymers are still melt-processable. Thus, the polyimides can be used for injection molding applications if the number of melt cycles is low respectively if the melting time is short.
The melt flowability was determined via melt flow index (MFI) measurements. Inventive polymer IPI 17 was selected for the testing. The MFI measurement was performed at 400° C. and showed that the polymer is extrudable. IPI 17 showed sufficiently good flowability to be extruded from the device as shown in
With the MFI results can be said that IPI 17 is processable from the melt and has a high Tg of 290° C. The gas formation can be useful if less dense extruded goods are desired.
If more dense products are needed, it was found that gas evolution during extrusion could be minimized or avoided if the polyimide was heat treated before extrusion at temperatures over the To preferably under vacuum, since chain movement is increased at this temperature allowing the impurity to be removed.
The polyimide from Example 39 of US 2008/0044684 A1 was reproduced. Table 15 shows molar composition of the amine mix as well as SEC and DSC results for the segmented polymers
CPI13 does have Tg clearly below 290° C.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22214870.2 | Dec 2022 | EP | regional |
