FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL / COMPLETE SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION :
An improved process for preparing high molecular weight polybenzimidazole and polybenzimidazole obtained therefrom.
2. APPLICANT
(a) NAME : SUDARSHAN CHEMICAL INDUSTRIES LTD.
(b) NATIONALITY: An Indian Company registered under the provisions of
the Companies Act, 1956.
(c) ADDRESS : 162, Wellesley Road,
PUNE- 411001, Maharashtra State, India.
3. PREAMBLE TO THE DESCRIPTION
PROVISIONAL COMPLETE
The following specification describes the The following specification
Invention. particularly describes the invention and
the manner in which it is to be
performed.
4. DESCRIPTION (Description starts from page 2)
5. CLAIMS; Given on a separate sheet
6. DATE AND SIGNATURE: Given at the end of last page of specification.
7. ABSTRACT OF THE INVENTION: Given on a separate sheet
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Technical Field:
The present invention relates to a preparation of high molecular weight polybenzimidazole. More particularly, present invention relates to a one pot polymerization of preparing polybenzimidazole by reacting 3,3',4,4'- tetraaminobiphenyl and diphenyl isopthalate in presence of an organophosphorous catalyst and diphenyl sulphone as reaction medium. The process provides quantitative yield with high molecular weight poly-2,2'- (m-phenylene)-5,5'-dibenzimidazole of improved colour and an inherent viscosity of minimum0.9 dl/g.
Background and Prior Art:
Polybenzimidazole (PBI) polymers are characterized by excellent thermal and mechanical stability. These PBI polymers are widely used as proton - conducting materials for fuel cell applications (Compare U.S Pat Nos. 2,895,948, 3,174947, 5,317,078 and 6,187,231.
The preparation of high molecular weight aromatic polybenzimidazoles by melt polymerization is disclosed in U.S Pat No. Re. 26,065 wherein an aromatic tetraamine and a diphenyl ester or an anhydride of an aromatic dicarboxylic are reacted at an elevated temperature and thereafter further polymerization is carried out in the solid state. According to this process, in order to produce polymers of sufficiently high molecular weight to be suitable for practical use it is necessary to finely pulverize the product of the melt polymerization prior to polymerization in the solid state and to conduct the solid state polymerization at an elevated temperature and in an inert gas stream over a prolonged period of time. Thus, the process requires several complicated operations. In addition, since the reaction is conducted over a long period of time at an elevated temperature, it tends to form insoluble and infusible polymers.
U.S. Pat. No. 3,313,783 describes a process adapted to overcome the above mentioned deficiencies. The process involves the solution polymerization of an inorganic
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acid salt of an aromatic tetramine and a dicarboxylic acid or a derivative thereof with heat in polyphosphoric acid. After completion of the reaction the polymer product is separated by pouring the reaction mixture in the form of solution into a large quantity of water. However , this preparation procedure is complicated and it is difficult to recover and reuse the polyphosphoric acid, thus obtained. Thus, this process is not generally considered satisfactory for the commercial production of polybenzimidazoles.
Another process for producing polybenzimidazoles is described in U.S Patent No. 3,509108. In the process the monomers are initially reacted in a melt phase polymerization at a temperature above 200 deg C and a pressure above 50 psi. The reaction product is then heated in a solid state polymerization at a temperature above 300 deg C to yield the final aromatic polybenzimidazole product. The process requires initial reaction be conducted at a pressure above 50 psi (preferably, between 300-600 psi) in order to control the foaming encountered during the polymerization.
U.S Patent No. 3,555,389 discloses the two stage process for the production of aromatic polybenzimidazoles. In this method, the monomers are heated at a temperature above 170 deg C in a first stage melt polymerization until a foamed prepolymer is formed. The foamed prepolymer is cooled, pulverized and introduced into a second stage polymerization where it is heated in the presence of phenol to yield a polybenzimidazole polymer product. As with the process of U.S. Patent Re.26,065, this process involves multiple operations and tends to form insoluble polymers.
U.S. Patent No.3,433,772 describes a two stage polymerization process for the production of aromatic polybenzimidazoles which utilize an organic additive, such as an alkane having 11-18 carbon aroms or a polycarbocyclic hydrocarbon, in order to control foaming during the first stage.
Further the melt polymerization process for the production of high molecular weight aromatic polybenzimidazole is described in U.S Patent No. 3,655,632. The process involves heating a mixture of an aromatic tetramine and an aromatic dinitrile in
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the presence of an ammonium salt of an inorganic acid or an organic sulfonic acid. The present states that generally it is considered impossible to obtain aromatic polybenzimidazoles, especially of high molecular weight, by merely heating a mixture of aromatic tetramines and aromatic dicarboxylic acids or derivatives thereof.
U.S. Patent No.4,312,976 describes a single stage melt polymerization process for producing polybenzimidazole which involves reacting a tetraminobiphenyl with a dicarboxylic acid in the presence of an acid catalyst such as p-toluenesulfonic acid.
The single stage melt polymerization processes which involves reacting a tetraaminobiphenyl with a dicarboxylic acid in the presence of organosilicone halide, phosphorous containing catalysts, tin containing catalyst as polymerization catalyst are disclosed in U.S. Patent No. 4,448,954,4,452,967 and 4,452,971 respectively.
Further single stage melt polymerization process disclosed in publication No. WO2006014213 wherein, tetraaminobiphenyl is reacted with diphenyl isophthalate under vacuum with inert gas sweep in absence of organo silicone and phosphorous containing polymeration catalyst. However, this process also requires several complicated operations.
U.S. Patent No. 3,784,517 discloses a one step process for preparing polybenzimidazoles that involves reacting an aromatic tetramino compound with the diphenyl ester or anhydride of an aromatic dicarboxylic acid in the presence of an aliphatic or aromatic sulfone solvent with aromatic hydrocarbon as another solvent. The reaction mixture is initially heated to boiling point of hydrocarbon, the temperature being maintained for the time sufficient to boil off aromatic hydrocarbon and then temperature is increased to boiling point of sulfone.
Thus any method for producing polybenzimidazole product with high molecular weight and high purity which is safer, easier to handle and overcomes the various disadvantages of the prior art procedures, would be very desirable.
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Description:
The present invention relates to a process for producing polybenzimidazole that comprises preparing mixture of 3,3', 4,4'- tetraminobiphenyl and diphenyl isophthalate, and heating the mixture in the presence of an phosphorous containing catalyst in aromatic sulfone solvent to provide an essentially quantitative yield of polybenzimidazole product with an improved Gardner colour specification.
Polybenzimidazoles are a known class of heterocyclic polymers which consist essentially of recurring units is prepared by the process of the present invention.
The polybenzimidazole of formula I prepared by the process of the present invention is poly-2,2'-(m-phenylene)-5,5'-dibenzimidazole as characterized by the recurring unit. The polymer of the present invention is prepared by reacting 3,3',4,4'-tetraminobiphenyl of formula (II) with diphenyl isophthalate of formula (III) in presence of Organo phosphorous catalyst and aromatic sulphone solvent at temperature ranging from about 250 deg C to 380 deg C as shown below.

According to the present invention, high molecular weight polybenzimidazole is produced by reacting the monomeric reactants described above. The monomeric reactants are reacted at a boiling temperature of aromatic sulfone as reaction medium.
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The polymerization of the present invention is conducted at atmospheric pressure. In a typical run an open polymerization system is used which is provided with a distillation column to remove the water and phenol which are produced as by products of the condensation-polymerisation reaction.
The reaction is conducted in a substantially oxygen-free atmosphere. For example, an inert gas such as nitrogen or argon can be continuously passed through the reaction zone during the polymerisation. The inert gas employed should be substantially oxygen-free.
The polymerisation process is conducted for a period of time sufficient to produce a high molecular weight polybenzimidazole product. The inherent viscosity of the polybenzimidazole product is an indication of its molecular weight. The high molecular weight polybenzimidazoles produced by the process of the present invention exhibit an inherent viscosity of minimum 0.9 dl/g when measured at a concentration of 0.1 g of the polymer in 25 ml of 97% H2SO4 at 25 deg C. In order to obtain a high molecular weight polybenzimidazole product, the polymerisation is conducted for a reaction period of at least about two hour, e.g.,a reaction period between about 2-10 hours.
The monomeric reactants in presence of the polymerisation catalyst in diphenyl sulfone as reaction medium can be heated to the polymerisation temperature by a stepwise heating process. For example, the monomeric reactants can be heated initially to a temperature to 185-210 deg C and maintained for 0-2 hours. The temperature of the reaction mixture can then be raised to 240- 270 deg C for 0-5 hours followed by to the desired poymerisation temperature and maintained for period of 2-10 hours.
The polymerisation catalyst is used in a quantity between about 0.1-1 weight percent, based on the total weight of monomeric material being reacted. In a typical polymerisation reaction the weight of polymerisation catalyst employed is in the range between about 0.2-0.4 percent, based on the total weight of monomeric material.
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In the present invention, the important aspect is the use of a phosphorus containing polymerisation catalysts. The polymerisation catalysts can be either triphenyl phosphine or triphenyl phosphite.
Thus, polymer obtained in present invention is readily soluble in cone. Sulphuric acid and it is completely soluble in N,N'- dimethyl acetamide containing 1-2% LiCl at reflux temperature.
Example
Into a four neck round bottom flask equipped with a nitrogen inlet and outlet, mechanical stirrer and a condenser were charged 900g diphenyl sulfone, 159g (0.5 mole) of diphenyl isophthalate and 0.32 g of triphenylphosphine with nitrogen protection. The mixture was stirred at room temperature under nitrogen purging for 15-45 minutes. The mixture was heated slowly to 160 deg C -190 deg C to make clear solution. 107. lg (0.5 mole) 3,3',4,4' tetraminobiphenyl was added and stirred for 10-30 minutes under nitrogen purging. The reaction pot temperature was slowly raised to 185 deg C - 210 deg C and hold at this temperature for 1-5 hours. The reaction mixture was then heated to 240 deg C -270 deg C in 1-2 hours and maintained reaction at this temperature for 1-5 hours. The by products phenol and water formed was distilled out continously. Then, the reaction temperature was further raised to 350 deg C in 1-2 hours and maintained at 350-380 deg C for period of 5-10 hours. The resultant yellowish orange suspension was cooled to 170 deg C and poured into 5 litres acetone and stirred for 2 hours. The product was filtered and washed twice in blender with acetone 2 litres, and 1 litre, respectively. The polymer was dried at 150 deg C for 10-16 hours.
Small amount of dry polymer (l00mg) was dissolved in 25 ml 97% sulphuric acid. The solution was filtered using a 0.45 teflon filter. The inherent viscosity was measured using an ubbelohde viscometer at 25(+/- 1) deg C. The inherent viscosity was in the range of 0.8-1.2 dLg
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Advantages of the Present Invention:
1. The present invention does not require unnecessary temperature control and is performed at lower temperature than conventional methods.
2. The present invention provides improved colour and with no formation of insoluble material.
3. The present invention provides high molecular weight polymer with inherent viscosity of minimum 0.9 dl/g.
4. The present invention provides high molecular weight polymer which is completely soluble in cone. Sulfuric acid and N,N- dimethylacetamide containing 2% LiCl at reflux temperature.
Variations:
1. Various bases which can be used are sodium ethoxide, potassium tert.butoxide,
sodium tert.butoxide, lithium ethoxide, potassium ethoxide and sodium methoxide.
2. Various solvents which can be used are methanol, xylene, toluene, ethanol,
dimethylformamide and dimethyl sulfoxide.
The embodiments of the invention as described above and the method disclosed of the present invention will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the spirit and scope of the invention which is defined by the scope of the following claims.
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We Claim:
1. An improved process for preparing high molecular weight polybenzimidazole of formula (I) comprises reacting 3,3',4,4'-tetraminobiphenyl of formula (II) with diphenyl isophthalate of formula (III) in presence of organo phosphorous catalyst and aromatic sulphone solvent at temperature ranging from about 250 deg C to 380 deg C as shown below.

2. An improved process for preparing high molecular weight polybenzimidazole of formula(I) as claimed in cliam 1 wherein the polymerization catalyst is triphenylphosphine or triphenyl phosphite.
3. A process as claimed in claim 1 wherein the polymerization reaction medium is diphenyl sulphone.
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4. A process as claimed in claim 1 wherein equimolar mixture of 3,3\4,4'-
tetraminobiphenyl and diphenyl isophthalate is polymerized.
5. A process as claimed in claim 1 wherein reaction is carried out in an inert atmosphere at atmospheric pressure.
6. A process as claimed in claim 1 substantially as herein described with reference to the example.
7. Polybenzimidazole prepared by the process as claimed in claims 1 to 6 above.


Dated this 18th September, 2006.

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Abstract
This invention relates to a process for preparing high molecular weight polybenzimidazole of formula (I) comprises reacting 3,3\4,4'-tetraminobiphenyl 0f formula (II) with diphenyl isophthalate of formula (III) in presence of organo phosphorous catalyst and aromatic sulphone solvent at temperature ranging from about 250 deg C to 380 deg C as shown below.