Description

The present invention relates to a process for the production of a thermoplastic polyimide (PI), the thermoplastic polyimide (PI) having a melting temperature TM(PI> and/or a glass transition temperature T _G (PI> and the process comprising the steps a) to c). The present invention further relates to a thermoplastic polyimide (PI) obtained by the inventive process, to a polyimide composition (PC) comprising at least one thermoplastic polyimide (PI) obtained by the inventive process and to a moulded article comprising the polyimide composition (PC).

Polyimides and imide-containing polymers belong to the high-performance polymers and feature excellent temperatures and chemical resistance, good electric properties, low water up-take and high dimensional stability, as well as an intrinsic flame retardancy. Currently, all commercially available polyimides with a significant market volume are amorphous with glass transition temperatures ranging from 200 to 360 °C and beyond, wherein polymer prices increase with increasing glass transition temperature values.

In general, polyimides are produced by polycondensation of diamines with tetracarboxylic acids or their derivatives (carboxylic acid anhydrides or the corresponding tetracarboxylic alkyl esters) in solution, in the melt or even in the solid state. The mechanism of this polycondensation proceeds in two steps via the formation of an acid amide intermediate (polyamic acid prepolymer), which subsequently undergoes cyclodehydration to the corresponding polyimide. Usually, the acid amide intermediate is obtained at lower temperatures, while the imide formation requires higher activation energies.

In case the polyimide is produced in solution, N-methyl pyrrolidone (NMP) is commonly used as solvent as it can dissolve the monomers and the polyamic acid prepolymer at room temperature as well as the final polyimide at elevated temperature.

WO 2018/032023 A1 discloses a method for producing polyimides by the polycondensation of previously produced stoichiometric salts from polycarboxylic acids or their polyanhydrides and polyamines, by heating the salts for dehydration, the method being characterised in that: a) an aqueous solution of a water-soluble stoichiometric salt is produced from polycarboxylic acid and polyamine; b) the aqueous solution undergoes a processing step; and c) the salt contained in the solution is simultaneously or subsequently polycondensed, by means of heating, to form a polyimide. WO 2013/041530 A1 describes a thermoplastic, semi-aromatic (co)polyimide obtained by polymerization of the following compounds: (a) at least one aromatic compound comprising 2 anhydride functions and/or its carboxylic acid and/or ester derivatives; and (b) one or more aliphatic diamines, in which said aliphatic diamine or diamines are chosen from the diamines of formula (I) NH2-R-NH2 with R being a saturated aliphatic hydrocarbon-based divalent radical, the two amine functions of which are separated by 4 to 6 carbon atoms, and of which 1 or 2 hydrogen atoms of the divalent radical are substituted by 1 or 2 methyl and/or ethyl groups; and optionally the diamines of formula (II) NH ₂ -R'-NH ₂ with R' being a divalent hydrocarbon, aliphatic, cycloaliphatic or arylaliphatic radical, saturated and/or unsaturated, which optionally comprises heteroatoms; or at least one ammonium carboxylate salt obtained from monomers (a) and (b). The (co)polyimide can be produced by solution polymerization, by solid state polymerization or by melt polymerization.

US 8,927,678 B2 discloses a crystalline thermoplastic copolyamide resin having a melting point of 360 °C or less and a glass transition temperature of 200 °C or more. The thermoplastic copolyamide resin can be produced by polymerizing a tetracarboxylic acid component and a diamine component, wherein the tetracarboxylic acid component contains a tetracarboxylic acid containing at least one aromatic ring and/or a derivative thereof, and the diamine component contains a diamine containing at least one alicyclic hydrocarbon structure and a chain aliphatic diamine. The polymerization is preferably carried out as suspension polymerization at a temperature in the range from 180 to 250 °C. As solvent a mixture of 2-(2-methoxyethoxy)ethanol and water is preferred.

US 4 221 897 A discloses a method for making polyetheramide acid imide or polyetherimide which comprises (A) heating a mixture at a temperature in the range of from 30° C to 250° C which is substantially free of organic solvent and which comprises by weight 20% to 95% of water, and 5% to 80% of a substantially equal molar mixture of organic diamine and a bis(ether dicarbonyl) compound, and (B) recovering the polyetheramide acid imide or polyetherimide from the mixture of (A).

US 2021/070940 A1 discloses a method for the manufacture of a poly(imide) prepolymer varnish, the method comprising, combining a bisanhydride powder or an organic diamine and a solvent comprising a C1-6 alcohol, water soluble ketone, water, or a combination comprising at least one of the foregoing to form a mixture; and adding an organic diamine or a bisanhydride powder to the mixture under conditions effective to form a poly(imide) prepolymer, provided that when the bisanhydride powder is combined with the solvent, the organic diamine is added to the mixture to form the poly(imide) prepolymer, and when the organic diamine is combined with the solvent, the bisanhydride powder is added to the mixture to form the poly(imide) prepolymer; wherein the method further comprises at least one of the following process steps: adding an effective amount of a secondary or tertiary amine to solubilize the poly(imide) prepolymer in the solvent; heating the mixture comprising the poly(imide) prepolymer to a temperature effective to provide a varnish; and agitating the mixture under conditions effective to provide a varnish; and wherein the poly(imide) prepolymer varnish has a residual organic diamine content of less than or equal to 1000 ppm.

However, disadvantages of the present processes for the production of polyimides (PI) are their elaborate and costly production and processing. For example, the polyamic acid prepolymer obtained in the intermediate step must often be isolated and purified before it can react further to form the polyimide. Furthermore, in case NMP is used as solvent, small amounts of a high-boiling aromatic solvent, like toluene, chloro-benzene or dichloro-benzene must be added to help remove the condensation water from the reaction mixture and drive the imide formation to completion. A further disadvantage are the high temperatures at which the cyclodehydration to the corresponding polyimide takes place.

It is thus an object of the present invention to provide a process for the production of a thermoplastic polyimide, which has the aforementioned disadvantages of the processes described in the prior art only to a lesser degree, if at all. The process shall be very simple and inexpensive to perform.

This object is achieved by a process for the production of a thermoplastic polyimide (PI), the thermoplastic polyimide (PI) having a melting temperature T _M (PI> and/or a glass transition temperature T _G (PI> and the process comprising the following steps a) to c) a) mixing at least the following components (A) to (C)

(A) at least one diamine,

(B) at least one tetracarboxylic acid compound and

(C) water to obtain a polycondensable mixture (pM) comprising water (C) and a first product (FP) of component (A), component (B) and optionally component (C), b) heating the polycondensable mixture (pM) obtained in step a) to a first temperature Ti to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and additional water (aW) released during polycondensation, and c) removing the water (C) and the additional water (aW) from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI), wherein the first temperature Ti is above the melting temperature TM<PI) and/or the glass transition temperature T _G (PI> of the thermoplastic polyimide (PI).

This object is further achieved by a process for the production of a thermoplastic polyimide (PI), the thermoplastic polyimide (PI) having a melting temperature TM(PI)I and/or a glass transition temperature TG(PI) and the process comprising the following steps a) to c) a) mixing at least the following components (A) to (C)

(A) at least one diamine,

(B) at least one tetracarboxylic acid compound and

(C) water to obtain a polycondensable mixture (pM) comprising water (C) and a first product (FP) of component (A), component (B) and optionally component (C), b) heating the polycondensable mixture (pM) obtained in step a) to a first temperature T1 to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and optionally additional water (aW) released during polycondensation, and c) removing the water (C) and, optionally, the additional water (aW) from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI), wherein the first temperature T1 is above the melting temperature TM<PI) and/or the glass transition temperature TG(PI) of the thermoplastic polyimide (PI), wherein the melting temperature TM ₍ PD and the glass transition temperature T GIPI\ are each determined by means of differential scanning calorimetry (DSC).

It has been found that, surprisingly, in the inventive process for the production of a thermoplastic polyimide (PI), the use of unpleasant high-boiling aromatic solvents can be avoided.

Furthermore, the thermoplastic polyimide (PI) produced by the inventive process exhibits a very low polydispersity M _w /M _n ; typically the thermoplastic polyimide (PI) has a polydispersity M _w /M _n < 5, preferably a polydispersity M _w /M _n < 4 and more preferably a polydispersity M _w /M _n < 3.5.

In addition, the thermoplastic polyimide (PI) produced by the inventive process has a high number average molecular weight M _n , preferably of 5 000 to 50 000 g/mol. A further advantage is that all steps a) to c) can be carried out in the same reaction vessel, which saves time and money as the first product (FP) does not have to be isolated and purified before it can react further to form the polyimide (PI).

The process for the production of the thermoplastic polyimide (PI) according to the invention is more particularly elucidated herein below.

The process for the production of the thermoplastic polyimide (PI) comprises the steps a) to c).

In step a), at least the following components (A) to (C)

(A) at least one diamine,

(B) at least one tetracarboxylic acid compound and

(C) water are mixed to obtain a polycondensable mixture (pM) comprising water (C) and a first product (FP) of component (A), component (B) and optionally component (C).

In the context of the present invention the terms "component (A)" and "at least one diamine" are used synonymously and therefore have the same meaning.

The same applies to the terms "component (B)" and "at least one tetracarboxylic acid compound". These terms are likewise used synonymously in the context of the present invention and therefore have the same meaning. Accordingly, "component (C)" and "water" are likewise used synonymously in the context of the present invention and therefore have the same meaning

Components (A), (B) and (C) can be mixed in any desired amounts.

For example,

5 to 30 % by weight of the at least one diamine (A),

25 to 45 % by weight of the at least one tetracarboxylic acid compound (B) and

45 to 55 % by weight of water (C), based in each case on the sum total of the percentages by weight of components (A), (B) and (C), are mixed in step a). The present invention therefore also provides a process in which

5 to 30 % by weight of the at least one diamine (A),

25 to 45 % by weight of the at least one tetracarboxylic acid compound (B) and

45 to 55 % by weight of water (C), based in each case on the sum total of the percentages by weight of components (A), (B) and (C), are mixed in step a).

In one embodiment,

45 to 55 % by weight of components (A) and (B), and

45 to 55 % by weight of water (C), based in each case on the sum total of the percentages by weight of components (A), (B) and (C), are mixed in step a), wherein the molar ratio of component (B) to component (A) is in the range of from 0.9 to 1.5 [mol/mol], preferably in the range of from 1 to 1 .1 [mol/mol], more preferably in the range of from 1 .005 to 1 .015 [mol/mol].

Processes for mixing are known to those skilled in the art. For example, components (A), (B) and (C) may be mixed in a reaction vessel.

In a preferred embodiment, the mixing in step a) is carried out at a second temperature T ₂ , wherein the second temperature T ₂ is in the range from 15 to 100 °C, preferably in the range from 15 to 80 °C, more preferably in the range from 15 to 50 °C. Preferably, the mixing of components (A), (B) and (C), at the second temperature T ₂ , is carried out for a period in the range from 15 to 45 minutes.

The present invention therefore also provides a process in which the mixing in step a) is carried out at a second temperature T ₂ , wherein the second temperature T ₂ is in the range from 15 to 100 °C.

Preferably, components (A), (B) and (C) are stirred during step a).

Component (A)

In step a), at least one diamine (A) is mixed with components (B) and (C).

According to the invention, "at least one diamine" means either exactly one diamine or a mixture of two or more diamines. In one embodiment, the at least one diamine (A) is a linear or branched aliphatic diamine having 5 to 12 carbon atoms.

The present invention therefore also provides a process in which the at least one diamine (A) is a linear or branched aliphatic diamine having 5 to 12 carbon atoms.

Examples for suitable linear or branched aliphatic diamines having 5 to 12 carbon atoms are 1 ,5-pentamethylenediamine, 1 ,6-hexamethylenediamine, 1 ,7- heptamethylendiamine, 1 ,9-nonamethylenediamine, 1 ,8-nonamethylenediamine, 1 ,10- decamethylenediamine, 1 ,11 -undecamethylenediamine and 1 ,12- dodecamethylenediamine. Preferred linear or branched aliphatic diamines having 5 to 12 carbon atoms are 1 ,6-hexamethylenediamine, 1 ,9-nonamethylenediamine, 1 ,8- nonamethylenediamine, 1 ,10-decamethylenediamine and 1 ,12- dodecamethylenediamine.

In another embodiment, the at least one diamine (A) is an aromatic diamine. In the context of the present invention, the term “aromatic diamine” means that the at least one diamine comprises at least one aromatic ring.

The present invention therefore also provides a process in which the at least one diamine (A) is an aromatic diamine.

According to the invention, the aromatic diamine comprising at least one aromatic ring preferably comprises from 6 to 22 carbon atoms. Examples for suitable aromatic diamines are therefore phenylenediamines like 1 ,2-phenylenediamine (o- phenylenediamine), 1 ,3-phenylenediamine (m-phenylenediamine) and 1 ,4- phenylenediamine (p-phenylenediamine), xylylenediamines like 1 ,2-xylylenediamine (o- xylylenediamine), 1 ,3-xylylenediamine (m-xylylenediamine) and 1 ,4-xylylenediamine (p- xylylenediamine), 1 ,2-diethynylbenzenediamine, 1 ,3-diethynylbenzenediamine, 1 ,4- diethynylbenzenediamine, 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 1 ,5-diaminonaphthalene.

However, in another embodiment of the present invention, at least on diamine can be selected from a linear or branched aliphatic diamine having 5 to 12 carbon atoms and at least one further diamine can be selected from an aromatic diamine.

In an especially preferred embodiment, the at least one diamine (A) is a linear aliphatic diamine having 5 to 12 carbon atoms.

Component (B) In step a), at least one tetracarboxylic acid compound (B) is mixed with components (A) and (C).

According to the invention, "at least one tetracarboxylic acid compound" means either exactly one tetracarboxylic acid compound or a mixture of two or more tetracarboxylic acid compounds.

In the context of the present invention, the term “tetracarboxylic acid compound” includes not only tetracarboxylic acids, but also derivatives of the tetracarboxylic acids. Examples for suitable derivatives of the tetracarboxylic acids are the corresponding carboxylic acid anhydrides and the corresponding tetracarboxylic alkyl esters.

Examples for suitable tetracarboxylic acids are tetracarboxylic acids comprising at least one aromatic ring. Preferably, the tetracarboxylic acids comprising at least one aromatic ring are compounds having four carboxyl groups that are bonded directly to the aromatic ring and may comprise an alkyl group. The tetracarboxylic acids preferably have from 6 to 26 carbon atoms.

Especially preferred tetracarboxylic acids include pyromellitic acid, 2, 3,5,6- toluenetetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 3, 3', 4,4'- biphenyltetracarboxylic acid and 1 ,4,5,8-naphthalenetetracarboxylic acid. Among these, pyromellitic acid is particularly preferred.

Examples of the derivatives of the tetracarboxylic acid comprising at least one aromatic ring include an anhydride and an alkyl ester of a tetracarboxylic acid comprising at least one aromatic ring. Derivatives of the tetracarboxylic acid preferably have from 6 to 38 carbon atoms.

Examples of suitable anhydrides of the tetracarboxylic acid include pyromellitic monoanhydride, pyromellitic dianhydride, 2,3,5,6-toluenetetracarboxylic dianhydride, 4,4'-(4,4'-lsopropylidenediphenoxy)bis(phthalic anhydride), 3, 3', 4,4'- diphenylsulfonetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1 ,4,5,8- naphthalenetetracarboxylic dianhydride.

Examples of suitable alkyl esters of the tetracarboxylic acid include dimethyl pyromellitate, diethyl pyromellitate, dipropyl pyromellitate, diisopropyl pyromellitate, dimethyl 2,3,5,6-toluenetetracarboxylate, tetramethyl 1 ,2,4,5-benzenetetracarboxylate, dimethyl 3,3',4,4'-diphenylsulfonetetracarboxylate, dimethyl 3, 3', 4,4'- benzophenonetetracarboxylate, dimethyl 3,3',4,4'-biphenyltetracarboxylate and dimethyl 1 ,4,5,8-naphthalenetetracarboxylate. The alkyl group in the alkyl esters of the tetracarboxylic acid preferably have from 1 to 3 carbon atoms. Most preferably, the at least one tetracarboxylic acid compound (B) is a pyromellitic acid compound.

The invention therefore also provides a process in which the at least one tetracarboxylic acid compound (B) is a pyromellitic acid compound.

According to the invention, a pyromellitic acid compound includes not only pyromellitic acid, but also derivatives of the pyromellitic acid. Examples for pyromellitic acid compounds are pyromellitic acid, pyromellitic monoanhydride, pyromellitic dianhydride, dimethyl pyromellitate, diethyl pyromellitate, dipropyl pyromellitate and diisopropyl pyro mellitate, tetramethyl 1 ,2,4,5-benzenetetracarboxylate, tetraethyl 1 ,2,4,5- benzenetetracarboxylate, tetrapropyl 1 ,2,4,5-benzenetetracarboxylate and tetraisopropyl 1 ,2,4,5-benzenetetracarboxylate.

Especially preferred as the at least one tetracarboxylic acid compound (B) is pyromellitic dianhydride.

Component (C)

In step a), water (C) is mixed with components (A) and (B).

Polycondensable mixture (pM)

Components (A), (B) and (C) are mixed to obtain a polycondensable mixture (pM) comprising water (C) and a first product (FP) of component (A), component (B) and optionally component (C).

First products (FP) of component (A), component (B) and optionally component (C) are known to those skilled in the art.

As first product (FP), for example, an acid amide intermediate (polyamic acid prepolymer) can be obtained which is an addition product only of component (A) and component (B), typically in case component (A) is at least one diamine (A) and component (B) is at least one carboxylic acid anhydride. However, the water (C) can also react with components (A) and (B), wherein as first product (FP) also the respective diamine salt can be obtained. The acid amide intermediate (polyamic acid prepolymer) and the respective diamine salt are typically in equilibrium with each other via continuous hydrolysis and condensation reactions. In case component (B) is at least one tetracarboxylic acid or at least one alkyl ester of the tetracarboxylic acid, the first product (FP) is a condensation product of components (A) and (B). According to the invention, the term “first product (FP)” therefore includes the addition product of components (A) and (B), the diamine salt and the condensation product of components (A) and (B).

Further, the polycondensable mixture (pM) can also comprise addition products of component (A) and water (C) and/or addition products of component (B) and water (C).

It is clear for a skilled person that the amount of the water (C) is reduced in case it reacts with components (A) and/or (B).

Further it is also clear for a skilled person that the polycondensable mixture (pM) can also comprise unreacted component (A) and unreacted component (B). Further, in case component (B) is at least one alkyl ester of the tetracarboxylic acid, the polycondensable mixture (pM) can also comprise the corresponding alkyl alcohol.

Step a-2)

In one embodiment of the present invention, between step a) and step b), a further step a-2) is carried out, in which the polycondensable mixture (pM) obtained in step a) is heated to a third temperature T ₃ being in the range from 225 to 275 °C. Preferably, the heating of the polycondensable mixture (pM) obtained in step a) at the third temperature T ₃ is carried out for a period in the range from 15 to 45 minutes.

The present invention therefore also provides a process in which between step a) and step b), a further step a-2) is carried out, in which the polycondensable mixture (pM) obtained in step a) is heated to a third temperature T ₃ being in the range from 225 to 275 °C.

Preferably, step a-2) is carried out in the same reaction vessel as step a).

The barrel temperature of the reaction vessel can be higher than the temperature of the components in the reaction vessel, and it is equally possible that the barrel temperature of the reaction vessel is lower than the temperature of the components in the reaction vessel. By way of example, it is possible that the barrel temperature of the reaction vessel is initially higher than the temperature of the components in the reaction vessel when the components are heated. When the components in the reaction vessel are cooled, it is possible that the barrel temperature of the reaction vessel is lower than the temperature of the components in the reaction vessel. The temperatures given in the present invention and referring to the reaction vessel are meant to be barrel temperatures of the reaction vessel. "Barrel temperature of the reaction vessel" means the temperature of the barrel of the reaction vessel. The barrel temperature of the reaction vessel is therefore the temperature of the external wall of the reaction vessel barrel. As reaction vessel, any reaction vessel known to the skilled person is suitable which can be used at the temperatures and pressures during the production of a thermoplastic polyimide (PI). In general, the reaction vessel can be heated to at least a temperature above the melting temperature TM<PI) and/or the glass transition temperature T _G(P i) of the thermoplastic polyimide (PI).

Preferably, the polycondensable mixture (pM) is stirred during step a-2).

Step b)

In step b), the polycondensable mixture (pM) obtained in step a) is heated to a first temperature Ti to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and additional water (aW) released during polycondensation, wherein the first temperature Ti is above the melting temperature TM(PI) and/or the glass transition temperature T _G(P i) of the thermoplastic polyimide (PI). Preferably, the heating of the polycondensable mixture (pM) obtained in step a) at the first temperature Ti is carried out for a period in the range from 10 to 60 minutes.

In the context of the present invention, the term “wherein the first temperature Ti is above the melting temperature TM<PI) and/or the glass transition temperature T _G(P i) of the thermoplastic polyimide (PI)” means that, in case the polyimide (PI) only has a glass transition temperature T _G(P i) (amorphous polyimide (PI)), the first temperature Ti is above this glass transition temperature T _G(P i), and that in case the polyimide (PI) has a melting temperature TM<PI), the first temperature Ti is above this melting temperature TM(PI). Further, it means that, in case the polyimide (PI) has a melting temperature TM<PI) and a glass transition temperature T _G(P i) (semi-crystalline polyimide (PI)), the first temperature Ti is above the melting temperature TM<PI).

Preferably, the first temperature Ti is in the range from 250 to 400 °C, more preferably in the range from 260 to 375 °C, most preferably in the range from 270 to 350 °C.

The present invention therefore also provides a process in which the first temperature Ti is in the range from 250 to 400 °C.

Preferably, step a-2) is carried out in the same reaction vessel as steps a) and a-2). The polycondensable mixture (pM) is also preferably stirred during step b).

Polycondensation product mixture (ppM)

In on embodiment in step b), the polycondensable mixture (pM) obtained in step a) is heated to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and additional water (aW) released during polycondensation.

It is clear for a skilled person that during step b), a polycondensation reaction takes place, wherein the first product (FP) is cyclo-dehydrated to the corresponding polyimide (PI). Thereby, additional water (aW) is released, so that the obtained polycondensation product mixture (PPM) comprises the thermoplastic polyimide (PI), the water (C) and additional water (aW) released during polycondensation. This holds true in case component (B) is a tetracarboxylic acid, a carboxylic acid anhydride or a tetracarboxylic alkyl ester with less than four ester functions.

In case component (B) is a tetraalkyl ester, for example, tetramethyl 1 , 2,4,5- benzenetetracarboxylate, the polycondensation product mixture (PPM) comprises, instead the additional water (aW), the respective alcohol released during polycondensation.

Therefore, in another embodiment, in step b), the polycondensable mixture (pM) obtained in step a) is heated to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and optionally additional water (aW) released during polycondensation.

Step c)

In step c), the water (C) and the additional water (aW) are removed from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI).

In another embodiment, in step c), the water (C) and, optionally, the additional water (aW) are removed from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI).

Step c) is preferably carried out in the same reaction vessel as steps a), a-2) and b).

Therefore, the present invention also provides a process in which steps a), b), c) and optionally step a-2) are carried out in the same reaction vessel.

During step c), the first temperature Ti is preferably held. Therefore, the temperature during step c) is also preferably in the range from 250 to 400 °C, more preferably in the range from 260 to 375 °C, most preferably in the range from 270 to 350 °C.

Thermoplastic polyimide (PI) In step c), the water (C) and the additional water (aW) are removed from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI).

Therefore, the present invention also provides a thermoplastic polyimide (PI) obtained by the process of the invention.

The thermoplastic polyimide (PI) preferably has a number average molecular weight M _n in the range from 5 000 to 50 000 g/mol, more preferably in the range from 10 000 to 40 000 g/mol. The number average molecular weight M _n is determined by gel permeation chromatography (GPC). Hexafluoro-2-propanol/0.05 % potassium trifluoroacetate was used as solvent and narrowly distributed polymethylmethacrylate was used as standard in the measurement.

The present invention therefore also provides a process in which the thermoplastic polyimide (PI) has a number average molecular weight M _n of 5 000 to 50 000 g/mol.

The thermoplastic polyimide (PI) preferably has a polydispersity M _w /M _n < 5, more preferably a polydispersity M _w /M _n < 4 and most preferably a polydispersity M _w /M _n < 3.5.

The present invention therefore also provides a process in which the thermoplastic polyimide (PI) has a polydispersity M _w /M _n < 5.

In a most preferred embodiment, the thermoplastic polyimide (PI) has a polydispersity Mw/M _n in the range from 2.5 to 3.5.

The thermoplastic polyimide (PI) typically has a viscosity number (VN) in the range from 50 to 300 mL/g, preferably in the range from 70 to 280 mL/g. The viscosity number is determined according to the invention from a 0.5 wt% solution of the polyimide (PI) in 96 wt% sulfuric acid at 25°C according to ISO 307.

In case, the at least one diamine (A) is a linear or branched aliphatic diamine having 5 to 12 carbon atoms, the obtained thermoplastic polyimide (PI) is typically a semicrystalline thermoplastic polyimide (PI) having a melting temperature TM(PI» in the range from 220 to 380°C, preferably in the range from 270 to 350°C, and a glass transition temperature T _G (PI> in the range from 80 to 180 °C.

The present invention therefore also provides a process in which the thermoplastic polyimide (PI) is a semi-crystalline thermoplastic polyimide (PI) having a melting temperature T _M <PI) in the range from 220 to 380°C and a glass transition temperature T _G (PI) in the range from 80 to 180 °C. In case, the at least one diamine (A) is an aromatic diamine, the obtained thermoplastic polyimide (PI) is typically an amorphous thermoplastic polyimide (PI) having a glass transition temperature T _G(P i) in the range from 150 to 275 °C.

The present invention therefore also provides a process in which the thermoplastic polyimide (PI) is an amorphous thermoplastic polyimide (PI) having a glass transition temperature T _G(P i) in the range from 150 to 275 °C.

The melting temperature T _M (PI> and the glass transition temperature T _G(P i) of the thermoplastic polyimides (PI) were each determined by means of differential scanning calorimetry (DSC).

For determination of the melting temperature TM(PI>, a first heating run (H1 ) at a heating rate of 20 K/min was measured. The melting temperature T _M (PI> then corresponded to the temperature at the maximum of the melting peak of the heating run (H1).

For determination of the glass transition temperature T _G(P i), after the first heating run (H1 ), a cooling run (C) and subsequently a second heating run (H2) were measured. The cooling run was measured at a cooling rate of 20 K/min; the first heating run (H1) and the second heating run (H2) were measured at a heating rate of 20 K/min. The glass transition temperature T _G(P i) was then determined at half the step height of the second heating run (H2).

Due to the temperature above the melting temperature T _M <PI) and/or the glass transition temperature T _G(P i) of the thermoplastic polyimide (PI), at the end of step c), the thermoplastic polyimide (PI) is in the molten state. Therefore, it can be released into a water bath to obtain a strand and then granulated; or it can directly be fed into an underwater pelletiser.

Thus, the present invention also provides a process in which after step c) the thermoplastic polyimide (PI) is processed to a strand or to granulate.

Polyimide composition (PC)

A further subject of the present invention is a polyimide composition (PC) comprising at least one thermoplastic polyimide (PI) obtained by the inventive process, optionally at least one additive and optionally at least one filler. The present invention therefore also provides a polyimide composition (PC) comprising at least one thermoplastic polyimide (PI) obtained by the inventive process, optionally at least one additive and optionally at least one filler.

According to the invention, the polyimide composition (PC) comprises at least one polyimide (PI), optionally at least one additive and optionally at least one filler.

In the context of the present invention "at least one polyimide (PI)" is to be understood as meaning either precisely one polyimide (PI) or else a mixture of two or more polyimides (PI).

The same applies for "at least one additive". In the context of the present invention "at least one additive" is to be understood as meaning either precisely one additive or else a mixture of two or more additives. Accordingly, “at least one filler” is also to be understood as meaning either precisely one filler or else a mixture of two or more fillers.

The polyimide composition (PC)comprises the at least one polyimide (PI), optionally the at least one additive and optionally the at least one filler in any desired amounts.

It is preferable when the polyimide composition (PC) comprises in the range from 25 to 100 % by weight of the at least one polyimide (PI), in the range from 0 to 5 % by weight of the at least one additive and in the range from 0 to 70 % by weight of the at least one filler, in each case based on the sum of the weight percentages of the at least one polyimide (PI), the at least one additive and the at least one filler, preferably based on the total weight of the polyimide composition (PC).

The % by weight values of the at least one polyimide (PI) present in the polyimide composition (PC), of the optionally present at least one additive and of the optionally present at least one filler thus typically sum to 100%.

Suitable additives are known per se to those skilled in the art. The additives are preferably selected from the group consisting of stabilizers, dyes, pigments, impact modifiers and plasticizers.

Suitable stabilizers are for example phenol, talc, alkaline earth metal silicates, sterically hindered phenols, phosphites and alkaline earth metal glycerophosphates. Suitable dyes and pigments are for example transition metal oxides or nigrosins.

Suitable impact modifiers are for example polymers based on ethylene propylene (EPM) or ethylene propylene diene (EPDM) rubbers or thermoplastic urethanes and also ionomers or styrene-based rubbers.

Suitable plasticizers are for example dioctyl phthalate, dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oils, N-(n-butyl)-benzenesulfonamide and ortho- and paratolylethylsulfonamide.

Suitable fillers are also known per se to those skilled in the art. The fillers are preferably selected from the group consisting of glass beads, glass fibers, kaolin, wollastonite, muscovite, phlogopite, carbon fibers, carbon nanotubes and chalk.

It is also possible that the polyimide composition (PC) comprises at least one polymer selected from polymers different from the at least one thermoplastic polyimide (PI), for example, from polyamides, polyesters, polysulfones, thermoplastic polyurethanes (TPU) and polyolefins like polyethylene and polypropylene.

The polyimide composition (PC) may be produced by any method known to those skilled in the art. Preferably, it is produced by compounding. Processes for compounding are known to those skilled in the art.

Moulded article

A further object of the present invention is a moulded article comprising the inventive polyimide composition (PC).

The present invention therefore also provides a moulded article comprising the inventive polyimide composition (PC).

The moulded articles comprising the polyimide composition (PC) can be produced by forming the polyimide composition (PC).

The polyimide composition (PC) may be formed by any methods known to the skilled person to produce the moulded articles. Examples of suitable forming methods include injection moulding, extrusion, calendering, rotomoulding and blow moulding. The polyimide composition (PC) is preferably formed by injection moulding and/or extrusion, more preferably by injection moulding.

The invention is elucidated in detail hereinafter by examples, without restricting it thereto. used

Diamine (A)

(A1 ) 1 ,10-decamethylene diamine (DMDA; Sigma Aldrich)

(A2) 1 ,6-hexamethylene diamine (HMDA; BASF SE)

(A3) Aliphatic C9-diamine mixture (Mitsui)

(A4) 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Sigma Aldrich)

(A5) m-phenylenediamine (1 ,3-phenylenediamine; Sigma Aldrich)

Tetracarboxylic acid compound (B)

(B1 ) pyromellitic dianhydride (PMDA; Sigma Aldrich)

(B2) 4,4'-(4,4'-lsopropylidenediphenoxy)bis(phthalic anhydride) (Sigma Aldrich)

Water (C)

General The number average molecular weight M _n is determined by gel permeation chromatography (GPC). Hexafluoro-2-propanol/0.05 % potassium trifluoroacetate was used as solvent and narrowly distributed polymethylmethacrylate was used as standard in the measurement.

The viscosity number (VN) is determined according to the invention from a 0.5 wt% solution of the polyimide (PI) in 96 wt% sulfuric acid at 25°C according to ISO 307.

AEG indicates the amino end group concentration. This is determined by means of titration. For determination of the amino end group concentration (AEG), 1 g of the component (thermoplastic polyimide) was dissolved in 30 mL of a phenol/methanol mixture (volume ratio of phenokmethanol 75:25) and then subjected to potentiometric titration with 0.2 N hydrochloric acid in water.

The melting temperature TM(PI> and the glass transition temperature T _G(P i) of the thermoplastic polyimides were each determined by means of differential scanning calorimetry (DSC).

For determination of the melting temperature TM<PI), a first heating run (H1) at a heating rate of 20 K/min was measured. The melting temperature TM(PI> then corresponded to the temperature at the maximum of the melting peak of the heating run (H1).

For determination of the glass transition temperature T _G(P i), after the first heating run (H1 ), a cooling run (C) and subsequently a second heating run (H2) were measured. The cooling run was measured at a cooling rate of 20 K/min; the first heating run (H1 ) and the second heating run (H2) were measured at a heating rate of 20 K/min. The glass transition temperature T _G(P i) was then determined at half the step height of the second heating run (H2).

Production of the thermoplastic polyimide (PI)

Step a)

In a 5L steel pressure reaction vessel equipped with a stirrer unit, components (A1), (A2), (A3), (A4), (A5), (B1 ), (B2) and (C) are mixed in the amounts reported in table 1 and stirred for 30 minutes (45 min for I4) to obtain a polycondensable mixture (pM) comprising water (C) and a first product (FP) of component (A), component (B) and optionally component (C). Table 1

Step a-2)

After step a), the polycondensable mixture (pM) obtained in step a) is heated to 250 °C in the pressure reaction vessel and kept there for another 30 minutes (11 , I3, I4, I5) (for another 10 minutes (I2)).

Step b)

After step a-2), the polycondensable mixture (pM) is heated to 345 °C to obtain a polycondensation product mixture (PPM) comprising the thermoplastic polyimide (PI), the water (C) and additional water (aW) released during the polycondensation.

Step c)

The water (C) and the additional water (aW) are removed from the polycondensation product mixture (PPM) obtained in step b) to obtain the thermoplastic polyimide (PI) by slowly opening the exhaust valve.

The properties of the obtained thermoplastic polyimides (PI) are shown in table 2.

Table 2

The polyimide (PI) according to inventive example (12) is used for the preparation of a polyimide composition (PC) and for the preparation of moulded articles comprising the polyimide composition (PC):

The polyimide (PI) according to 12 is compounded in a Haake Polylab QC equipped with a CTW100 extruder at 320°C (inlet) to 300°C (outlet). The injection-moulding is done on an Arburg 19. The processing and mould temperatures are set to 320°C and 90°C, respectively.

Subsequently, the properties of the tensile bars obtained are determined. The resultant tensile bars are tested in the dry state after drying at 80°C for 336 h under reduced pressure. In addition, Charpy bars are likewise tested under dry conditions (according to ISO179-2/1 ell: 1997 + Amd.1 :2011 ). The properties of the tensile bars obtained are also tested in the conditioned state (336 h, 70°C and 62% RH (relative humidity)).

The tensile strength, tensile modulus of elasticity and elongation at break is determined according to ISO 527-1 :2012.

The results are shown in table 3.

Table 3

¹ Properties were measured at 23°C