DESC:FIELD
The present disclosure relates to polyetherimide.
BACKGROUND
Polyetherimides are high performance engineering thermoplastics having high strength and rigidity at elevated temperatures, long term heat resistance, dimensional stability and good electrical properties.
Polyetherimides are amorphous, amber-to-transparent thermoplastics with characteristics similar to that of polyether ether ketone (PEEK). However, polyetherimides are less expensive as compared to PEEK. Polyetherimides find applications in diverse fields such as electronics, automobile industry, aircraft interiors, medical appliances, and the like.
Conventionally polyetherimides are prepared by reacting organic diamines with aromatic bis(ether anhydride)s. However, these processes are slow and take relatively longer period of time for completion.
Due to the increasing demand for polyetherimides, there is felt a need for developing an efficient and economical process for preparing polyetherimides, which can be completed in a relatively shorter duration of time.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
An object of the present disclosure is to provide a process for preparing polyetherimides.
Another object of the present disclosure is to provide a process for preparing polyetherimides, which can be completed in a relatively shorter duration of time.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
The present disclosure relates to a process for preparing polyethermides, the process comprises dehydrating bis(ether tetracarboxylic acid) by heating with cresylic acid and a fluid medium, azeotropically at a temperature in the range of 145 °C to 165 °C to obtain a first mixture comprising bis(ether anhydride). The bis(ether anhydride) is polymerized with at least one diamine in the presence of an accelerator by heating the first mixture with diamine at a temperature in the range of 130 °C to 160 °C for a time period in the range of 1 hour to 6 hours to obtain a second mixture containing the polyetherimide. Next, at least one end capping agent is added to the second mixture to obtain a third mixture, followed by cooling the third mixture to a temperature in the range of 90 °C to 110 °C to obtain a cooled mixture. The cooled mixture is drowned in an alcohol for a predetermined time period to obtain a fourth mixture, which is filtered to obtain a filtrate and a residue. The residue is purified by drying and washing to obtain the polyetherimide.
The bis(ether tetracarboxylic acid) of the present disclosure is at least one selected from the group consisting of 4,4’-((propane- 2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid, and 4,4'-([1,1'-biphenyl]-4,4'-diylbis(oxy))diphthalic acid and 4,4'-((sulfonylbis(4,1-phenylene))bis(oxy))diphthalic acid.
The diamine of the present disclosure is meta-phenylenediamine, and the accelerator is at least one selected from the group consisting of 3-methylpyridine (beta-picoline), and iso-quinoline. The end capping agent is at least one selected from the group consisting of phthalic anhydride, aniline, 4-phenoxy aniline, ortho-methyl aniline, meta-methyl aniline, and p-methyl aniline.
DETAILED DESCRIPTION
Polyetherimides are generally prepared by reacting organic diamines with aromatic bis(ether anhydride)s. However, these processes are slow and take a relatively longer time period for completion. The present disclosure envisages a process for preparing polyetherimides, which is simple and can be completed in a relatively short duration of time.
In accordance with an aspect of the present disclosure, there is provided a process for the preparation of polyetherimide. Polyetherimide, prepared by the process of the present disclosure is represented by Formula-I, given below:

Formula-I

wherein, ‘Ar’ represents an aromatic compound, selected from, 4,4'-diphenylpropane, 4,4’-(1,1’-biphenyl) and 4,4’-diphenylsulfone.
In the process of the present disclosure, the polyetherimide is prepared by reacting bis(ether anhydride) of Formula III and diamine in the presence of an accelerator. The bis(ether anhydride) can be prepared from the corresponding bis(ether tetracarboxylic acid) of Formula II by dehydration.

wherein, ‘Ar’ represents an aromatic compound, selected from, 4,4'-diphenylpropane, 4,4’-(1,1’-biphenyl) and 4,4’-diphenylsulfone,

Initially, bis(ether tetracarboxylic acid) is dehydrated with cresylic acid and a fluid medium to obtain a first mixture comprising bis(ether anhydride). The step of dehydration is carried out by heating bis(ether tetracarboxylic acid) with cresylic acid and the fluid medium at a temperature in the range of 145 °C to 165 °C. The heating is done to enable the azeotropic distillation, which helps in removing the water formed in the reaction vessel during the reaction from the reaction vessel.
In accordance with one embodiment of the present disclosure, the bis(ether tetracarboxylic acid) is at least one selected from the group consisting of 4,4'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid 4,4'-([1,1'-biphenyl]-4,4'-diylbis(oxy))diphthalic acid, and 4,4'-((sulfonylbis(4,1-phenylene))bis(oxy))diphthalic acid.
Cresylic acid is a mixture of phenol, ortho-cresol, meta-cresol, para-cresol and dimethyl phenols. It is used for dehydrating bis(ether tetracarboxylic acid). Cresylic acid is vacuum distilled before use at a temperature in the range of 100 °¬C to 120 °C (50 – 20 mm Hg reduced pressure) to obtain purified cresylic acid. The pyridine content of purified cresylic acid is in the range of 0.05 % to 0.06 %, which is within the permitted limit.
In one embodiment of the present disclosure, the use of cresylic acid ensures control of the polymerization reaction, to obtain a polymer having a desired molecular weight.
Next, the bis(ether anhydride) is polymerized with a diamine in the presence of an accelerator. The first mixture is heated with diamine under stirring at a temperature in the range of 130 °C to 160 °C, to obtain a second mixture containing polyetherimide. Polyethermide obtained in the process of the present disclosure is in completely dissolved form in cresylic acid at the temperature of polymerization.
Typically, the first mixture is cooled to a temperature in the range of 120 °C to 140 °C, before the addition of the diamine .
The diamine used in the present disclosure can be meta-phenylenediamine. Typically, meta-phenylenediamine can be dissolved in cresylic acid or molten meta-phenylenediamine is then added slowly to the first mixture.
In accordance with the present disclosure, the accelerator is at least one selected from the group consisting of an alkyl pyridine, typically, 3-methylpyridine (beta-picoline) and, iso-quinoline.
In accordance with the present disclosure, the fluid medium is at least one selected from the group consisting of toluene and xylene.
In accordance with the present disclosure, the molar ratio of the amount of the bis(ether tetracarboxylic acid) and the cresylic acid is in the range of 1:30 to 33.
In accordance with the present disclosure, the molar ratio of the amount of the bis(ether tetracarboxylic acid) to the amount of the fluid medium is in the range of 1:6 to 1:8.
In accordance with the present disclosure, the molar ratio of the amount of the bis(ether anhydride) to the amount of the diamine is in the range of 1:0.97 to 1:0.99.
In accordance with the present disclosure, the molar ratio of the amount of the bis(ether anhydride) to the amount of the accelerator is in the range of 1:0.02 to 1: 0.03.
It is observed that, the accelerator reduces the overall reaction time by 20 % to 40 %. For instance, without the accelerator, the reaction time is about 10 hours to 12 hours, whereas after addition of the accelerator, the reaction time is reduced to 4 hours to 6 hours. The accelerator is mostly recovered at the end of reaction and can be reused.
Samples are periodically removed and the average molecular weight of the polyetherimide formed is measured, using a chromatographic method, such as Gel Permeation Chromatography (GPC).
In one embodiment of the present disclosure, the desired molecular weight of the polyetherimide formed is in the range of 47,000 to 58,000 Daltons.
Next, the rate of reaction is determined and an end-capping agent is added to the second mixture to obtain a third mixture, so that when the polymerization ceases, the polyetherimide formed has the desired molecular weight.
In one embodiment of the present disclosure, the end-capping agent is at least one selected from the group consisting of phthalic anhydride (PAN) and aromatic amines selected from the group consisting of aniline, 4-phenoxy aniline, ortho-methyl aniline, meta-methyl aniline, and p-methyl aniline.
The end-capping agent may be dissolved in cresylic acid, before being added to the the second mixture to obtain a third mixture.
After the addition of the end-capping agent, the third mixture is maintained at a temperature in the range of 140 °C to 160 °C for a time period in the range of 1 hour to 3 hours. A resultant mixture containing the polymer of the desired molecular weight is thus obtained.
The starting materials and the polymer are soluble in cresylic acid at the temperature of polymerization. Due to higher solubility, the polymerization mixture obtained is homogeneous in nature, due to which the polymerization proceeds in a controlled manner resulting in a uniform polymer mass having narrow molecular weight distribution.
In the next step, the third mixture containing the polyetherimide is cooled to a temperature in the range of 90 °C to 110 °C to obtain a cooled mixture. Later, the cooled mixture containing the polyetherimide is drowned in an alcohol, preferably, methanol, for a time period in the range of 10 hours to 12 hours to obtain a fourth mixture, to isolate polyetherimide and the isolated polyetherimide is then separated by filtration.
The fourth mixture is filtered to obtain a residue and a filtrate. The residue so obtained by filtration is washed with a fluid medium, such as, methanol, followed by water washings. Samples of the washed polymer are drawn and the amount of cresylic acid is determined. The filtering and washing steps can be repeated till the amount of cresylic acid in the polymer is less than 0.1 %, followed by drying in the temperature range of 180 °C to 200 °C for 12 hours to 20 hours to obtain dried polyetherimide.
Scheme-I, below, illustrates the formation of anhydride and polyetherimide using 4,4'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid, wherein, 1 represents 4,4'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid, 2 represents the corresponding diphthalic acid dianhydride, 3 represents meta-phenylenediamine and 4 represents polyetherimide.

Scheme-I
The process of the present disclosure uses simple and easily available reactants. Also, the use of beta-picoline in the polymerization process reduces the overall reaction time, making the process significantly economical. The polyetherimide obtained by the process of the present disclosure can be further processed to obtain polymer strands, which can be used for various applications.
The present disclosure is further described in light of the following experiments which are set forth for illustration purpose only and are not to be construed for limiting the scope of the disclosure. The following experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial scale.
Experiment 1: Preparation of polyetherimide (PEI)
Cresylic acid (3 lit) was charged into a reaction vessel, followed by addition of a solution of 4,4'-((propane-2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid in toluene (556 gm in 1 lit toluene) to obtain a mixture. The mixture was heated at 155 ºC and the water formed during the reaction was removed azeotropically to obtain a first mixture comprising 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride (Bisphenol-A dianhydride). The first mixture was cooled to 140 ºC. A solution of meta-Phenylenediamine (MPDA) (107 gm meta-Phenylenediamine in 400 mL of cresylic acid ) was added to the cooled first mixture over a period of 30 minutes, followed by addition of toluene (600 mL) and phthalic anhydride solution (2.96 gm phthalic anhydride in 20 mL of cresylic acid ). The resultant mixture was heated to 150 ºC and water formed during the reaction was removed azeotropically to obtain a second mixture. After the completion of the reaction (that is when no water formation was observed), beta-Picoline (2 mL) was added while maintaining the temperature at 150 ºC for 6 hours. Samples of the reaction mass were removed periodically and the average molecular weight was checked by Gel permeation chromatography (GPC). When the average molecular weight of Polyetherimide was observed to be in the range of 50,000 to 60,000 a solution of phthalic anhydride (mixed with cresylic acid ) (11.84 gm) was added over a period of 10 minutes to obtain a third mixture, which was maintained at 150 ºC for another 2 hours followed by cooling to 100 ºC to obtain a cooled mixture.
The cooled mixture was drowned into methanol (5 lit), and stirred at 35 ºC for 2 hours to obtain a fourth mixture. The fourth mixture was then filtered to obtain a first residue and a first filtrate. Fresh methanol (5 lit) was added to the first residue and the resultant suspension was heated to reflux for 2 hours. The heated suspension was cooled to 35 ºC and filtered to obtain a second residue and a second filtrate. To the second residue was added de-mineralized water (5 lit) and stirred at 35 ºC for 2 hours, followed by filtration to obtain a third residue and a third filtrate. The third residue was washed with water and dried at 100 ºC and then at 200 ºC under reduced pressure to obtain polyetherimide (PEI).
The yield of PEI was found to be 90%. The glass transition temperature (Tg) of the polyetherimide, as measured by differential scanning calorimeter (DSC) was found to be 217 °C.
Example 2: Preparation of polyetherimide
Cresylic acid (3 lit) was charged into a reaction vessel, followed by addition of a solution of 4,4'-([1,1'-biphenyl]-4,4'-diylbis(oxy))diphthalic acid in toluene (514 gm in 1 liter toluene) to obtain a mixture. The mixture was heated at 155 ºC and the water formed during the reaction was removed azeotropically to obtain a first mixture comprising 5,5'-([1,1'-biphenyl]-4,4'-diylbis(oxy))bis(isobenzofuran-1,3-dione) (Biphenol dianhydride). The first mixture was cooled to 140 ºC. A solution of meta-Phenylenediamine (MPDA) (107 gm Phenylenediaminemixed with 400 mL cresylic acid ) (in ) was added over a period of 30 minutes to the cooled first mixture followed by addition of a solution of phthalic anhydride solution (2.96 gm phthalic anhydride in 20 mL of cresylic acid ) and toluene (600 mL). The reaction mixture was heated to 150 ºC and the water formed during the reaction was removed azeotropically. After the completion of reaction (that is when no water formation was observed), beta-Picoline (2 mL) was added while maintaining the temperature at 150 ºC for 6 hours to obtain a second mixture comprising polyethrimide. Samples of the reaction mass were removed periodically and the average molecular weight was checked by Gel permeation chromatography (GPC). When the average molecular weight of Polyetherimide was observed to be in the range of 50,000 to 60,000a solution of 4-phenoxyaniline in cresylic acid (14.8 gm) was added over a period of 10 minutes and reaction mixture was maintained at 150 ºC for 2 hours to obtain a third mixture, followed by cooling the third mixture to 100 ºC to obtain a cooled mixture.
The cooled mixture was drowned into methanol (5 lit), and stirred at 35 ºC for 2 hours to obtain a fourth mixture. The fourth mixture was then filtered to obtain a first residue and a first filtrate. Fresh methanol (5 lit) was added to the first residue and the resultant suspension was heated to reflux for 2 hours. The heated suspension was cooled to 35 ºC and filtered to obtain a second residue and a second filtrate. To the second residue was added de-mineralized water (5 lit) and stirred at 35 ºC for 2 hours, followed by filtration to obtain a third residue and a third filtrate. The third residue was washed with water and dried at 100 ºC and then at 200 ºC under reduced pressure to obtain polyetherimide.
The yield of polyetherimide-Bisphenol was found to be 95%. The glas transition temperature (Tg) as measured by differential scanning calorimeter (DSC) was found to be 248 °C.

Experiment 3: Preparation of polyetherimide (PEI)
Cresylic acid (3 lit) was charged into a reaction vessel, followed by addition of solution of 4,4'-((sulfonylbis(4,1-phenylene))bis(oxy))diphthalic acid in toluene (578 gm in 1 lit toluene) to obtain a mixture. The mixture was heated at 155 ºC and the water formed during the reaction was removed azeotropically to obtain a first mixture comprising 5,5'-((sulfonylbis(4,1-phenylene))bis(oxy))bis(isobenzofuran-1,3-dione) (Bisphenol-S dianhydride). The first mixture was cooled to 140 ºC. The solution of meta-Phenylenediamine (MPDA) (107 gm Phenylenediamine in 400 mL cresylic acid ) was added to the cooled first mixture over a period of 30 minutes, followed by addition of toluene (600 mL) and phthalic anhydride solution (2.96 gm phthalic anhydride in 20 mL of cresylic acid ). The resultant mixture was heated to 150 ºC and the water formed during the reaction was removed azeotropically to obtain a second mixture. After the completion of the reaction (that is when no water formation was observed), beta-Picoline (2 mL) was added while maintaining the temperature at 150 ºC for 6 hours. Samples of the reaction mass were removed periodically and the average molecular weight was checked by Gel permeation chromatography (GPC). When the average molecular weight of the polyetherimide was observed to be in the range of 50,000 to 60,000 a solution of phthalic anhydride (mixed with cresylic acid ) (11.84 gm) was added over period of 10 minutes to obtain a third mixture, which was maintained at 150 ºC for another 2 hours followed by cooling to 100 ºC to obtain a cooled mixture.
The cooled mixture was drowned into methanol (5 lit), and stirred at 35 ºC for 2 hours to obtain a fourth mixture. The fourth mixture was then filtered to obtain a first residue and a first filtrate. Fresh methanol (5 lit) was added to the first residue and the resultant suspension was heated to reflux for 2 hours. The heated suspension was cooled to 35 ºC and filtered to obtain a second residue and a second filtrate. To the second residue was added de-mineralized water (5 lit) and stirred at 35 ºC for 2 hours, followed by filtration to obtain a third residue and a third filtrate. The third residue was washed with water and dried at 100 ºC and then at 200 ºC under reduced pressure to obtain polyetherimide (PEI).
The yield of polyetherimide was found to be 95%. The glass transition temperature (Tg) as measured by differential scanning calorimeter (DSC) was found to be 265 °C.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process that is
-simple and economic;
- can be carried out in relatively short duration of time; and
- produces polyetherimide of desired molecular weight.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:1. A process for preparing polyetherimide of Formula I, said process comprising the following steps:

Formula I
wherein Ar represents an aromatic group,

i. dehydrating bis(ether tetracarboxylic acid) of Formula II by heating with cresylic acid in a fluid medium, azeotropically at a temperature in the range of 145 °C to 165 °C to obtain a first mixture comprising bis(ether anhydride) of Formula III;

wherein Ar represents an aromatic group

wherein Ar represents an aromatic group
ii. polymerizing said bis(ether anhydride) with at least one diamine in the presence of an accelerator by heating said first mixture with said diamine at a temperature in the range of 130 °C to 160 °C for a time period in the range of 1 hour to 6 hours to obtain a second mixture;
iii. adding at least one end capping agent to said second mixture to obtain a third mixture;
iv. cooling said third mixture to a temperature in the range of 90 °C to 110 °C to obtain a cooled mixture;
v. drowning said cooled mixture in an alcohol to obtain a fourth mixture;
vi. filtering said fourth mixture to obtain a filtrate and a residue; and
vii. drying and washing said residue to obtain said polyetherimide.

2. The process as claimed in claim 1, wherein said bis(ether tetracarboxylic acid) of Formula II is at least one selected from the group consisting of 4,4’-((propane- 2,2-diylbis(4,1-phenylene))bis(oxy)) diphthalic acid, 4,4'-([1,1'-biphenyl]-4,4'-diylbis(oxy))diphthalic acid and 4,4'-((sulfonylbis(4,1-phenylene))bis(oxy))diphthalic acid.
3. The process as claimed in claim 1, wherein said fluid medium is at least one selected from the group consisting of toluene and xylene.
4. The process as claimed in claim 1, wherein the molar ratio of the amount of said bis(ether tetracarboxylic acid) of Formula II to the amount of said cresylic acid is in the range of 1:30 to 1:33.
5. The process as claimed in claim 1, wherein the molar ratio of the amount of said bis(ether tetracarboxylic acid) of Formula II to the amount of said fluid medium is in the range of 1:6 to 1:8.
6. The process as claimed in claim 1, wherein the molar ratio of the amount of said bis(ether anhydride) of Formula III to the amount of said diamine is in the range of 1:097 to 1:0.99.
7. The process as claimed in claim 1, wherein the molar ratio of the amount of said bis(ether anhydride) of Formula III to the amount of said accelerator is in the range of 1:0.02 to 1:0.03.
8. The process as claimed in claim 1, wherein said diamine is meta-phenylenediamine.
9. The process as claimed in claim 1, wherein said accelerator is at least one selected from the group consisting of 3-methylpyridine(beta- picoline), and iso-quinoline.

10. The process as claimed in claim1 1, wherein said end capping agent is at least one selected from the group consisting of phthalic anhydride, aniline, 4-phenoxy aniline, ortho-methyl aniline, meta-methyl aniline, and p-methyl aniline.