FORM 2
The Patent Act 1970,
(39 of 1970)
&
The Patent rule 2003
Provisional Specification
(See Section 10 and Rule 13)
1. TITLE OF THE INVENTION
An improved process for the preparation of polyaryl ether nitriles
2. APPLICANT (S)
(a) Name: GHARDA CHEMICALS LIMITED.
(b) Nationality: INDIAN
(c) Address: B-27/29, MIDC, PHASE-1,
DOMBIVALI (E), DIST. THANE, 421 203, INDIA


3. PREAMBLE TO THE DESCRIPTION

The following specification describes the invention


TITLE : An improved process for the preparation of polyaryl ether nitrites
Field of Invention
This invention relates to a process for the preparation of polyaryl ether nitriles (PAEN) by the polymerization of dihalogeno nitrile with dihydroxy benzene in the presence of a suitable base in a aprotic solvent. This PAEN exhibits excellent heat resistance, solvent resistance and mechanical properties. PAEN have applications as materials for shafts and bearing for high load requirement, ultra small precision rotational parts, low warp grades for jigs and parts, in printing machine parts, and also in electronics, aerospace industries & defence applications. Their favorable properties, namely, crystallinity, high melting point and excellent mechanical properties class them with the best of engineering polymers. The excellent mechanical properties are even higher than that reported for the engineering polymers in the ketone and sulphone series and are attributed to dipole-dipole interactions of the nitrile groups.
Background of the Invention
Polyaryl ether nitriles (PAEN) are in the class of crystalline polymers having a high melting point such as Polyaryl ether ketone (PAEK). Examples of PAEK's are polyether ketone (PEK), polyether ether ketone (PEEK) and polyether ketone ketone (PEKK). The synthesis of these polymers presents difficulties because of their very low solubility in most organic solvents and the tendency of these polymers to precipitate from the solvent before sufficient molecular weight buildup had taken place. The discovery in the 1970's that aryl sulphones such as diphenyl sulphone, is able to dissolve the polyaryl ether ketones at temperatures in excess of 300°C, opened up the route to the synthesis of these polymers on a commercial scale The diphenyl sulphone is a high boiling point solvent, b.pt. 380°C, having excellent thermal stability. Therefore the synthesis of PAEK's at reaction temperatures of 300-330°C in diphenyl sulphone became possible. The polymer concentration is in the range of 300-400 gm/litre. On the contrary to synthesize PAEK in an aprotic solvent such as NMP at 200°C, a concentration of 30 gm/litre or less would be required (US 7217780), that is a four to five fold dilution.
l

Idemitsu Kosan introduced around 20 years ago a new class of crystalline polymer under the trademark PEN (poly aryl ether nitrile). Though during the first ten years after its introduction , many papers were published on PAEN, its synthesis and properties, during the last decade there has been only a few publications on this polymer. It is also not commercially available.
Polyaryl ether nitriles, (hereafter referred to as PAEN) are synthesized by the reaction of dihalo benzonitrile with dihydroxy benzene and can be represented by following general formula (I),

(I)
Where -Ar- represents mono cyclic, poly cyclic or fused aromatic ring systems selected from

and

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Polyaryl ether nitrile (PAEN) polymer obtained from reaction of resorcinol and dihalogeno benzonitrile has a repetitive units of aromatic rings connected through ether linkages and having pendant nitrile groups as shown by the following formula(ll).

(II)
Compounds categorized, as dihalogeno benzonitrile can be 2,6-dichloro benzonitrile (DCBN), 2,6-difluorobenzonitrile (DFBN) and 2,-chloro-6-fluoro-benzonitrile and more preferably 2,6-difluorobenzonitrile.

Where X represents chloro or fluoro.
The condensation reaction is carried out in polar aprotic solvent, more specifically in dimethyl sulfoxide, N-methyl pyrrolidone (NMP), sulpholane, N,N-dimethyl imidazolidone, preferably in N-methyl pyrrolidone. Alkali metal salts normally used include sodium or potassium carbonate or bicarbonate, preferably sodium carbonate.
EP 2430007B1 (assigned to Idemitsu) describes the synthesis of the polymer using 2,6 dichloro benzonitrile (DCBN), resorcinol (RS), potassium carbonate and N-methyl pyrrolidone as solvent at 190-200°C for 3 hrs. This patent describes the use of monovalent phenol, methyl chloride (CH3CI) and DFBN as endcapping agent. It also
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describes the use of alumina, Ti02 and aluminium powder as nucleating/crystallization agents.
US 4353443 discloses method of preparation of PAEN using DCBN, RS, potassium carbonate and NMP, and toluene for removing water azeotropically to obtain a polymer having reduced viscosity of 1.05 dl/gm at 190-200°C for 3 hrs.
JP H1-178552, JP S64-33153 & JP H1-146358 discloses the use of additives lite Ti02, Zeolite and different endcapping/blocking agents to improve the thermal stability of the polymer.
JP01-029426, describes the preparation of polymer with addition of pyridine hydrochloride to prevent the observed reduction of viscosity with time of polymerization by the applicant.
Journal of Polymer Science: Part A : Polymer Chemistry, Vol 31, 3439-3446 (1993) describes the synthesis of PAEN by the reaction of resorcinol and dihalogeno benzonitrile at 190-200X in the presence of a suitable base like sodium carbonate or potassium carbonate & suitable solvent leading to the formation of PAEN. The effect of various factors such as 2,6-difluorobenzonitrile versus 2,6-dichlorobenzonitrile, nature of the solvent used, temperature, concentration of the polymer in solvent, time period, etc. on the viscosity of the polymer is discussed. Optimum results are obtained using 2,6-difluorobenzonitrife, Na2CO2, concentration of PAEN in NMP of 200 gm/Litre or more and temperature of 200°C in 3-4 hours. With increase of concentration of polymer from 100 gm/Litre to 250 gm/Litre the maximum attainable inherent viscosity of PAEN increases proportionately from 0.5 dl/g to 1.4 dl/g.
Most of the literature on the synthesis of PAEN referred to above teaches the preparation of PAEN at high concentrations of polymer, around 200 gms/litre or more. The literature also reports that there is a tendency for the viscosity of the polymer to reduce with time of polymerization. This shows that the polymer produced has poor
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thermal stability. Hence the effort to introduce various additives such as pyridine hydrochloride to prevent the deterioration of the viscosity .
From the study of the literature cited above the synthesis of PAEN in NMP, at high concentrations is difficult and so this work was undertaken to study in more detail the process for the polymerization of PAEN and to develop a process which can reproducibly produce a polymer of desired quality, having the requisite mechanical and thermal properties.
Summary of the invention:
The synthesis of crystalline polyaryl ether nitriles presents a challenge as in the synthesis of polyaryl ether ketones described earlier. The reported solvent for the synthesis of PAEN is NMP. The comparatively lower boiling point of NMP, b.pt. of 200°C, and the poor thermal stability of NMP above this temperature limits the maximum polymerization temperature to 200°-205°C. But this presents the added problem of maintaining the polymer in solution to enable the polymer chains to grow. During our extensive research we found that at the temperatures of the polymerization reaction of 200°C, the polymer tends to precipitate from the reaction mass as the molecular weight builds up. Once the polymer has precipitated then redissolution of the polymer is difficult at the reaction temperatures of 200°C. We have also found that the thermal stability of such precipitated polymers in the reaction system at 200°C is poor. Hence we have directed our research at methods of maintaining the polymer in solution in NMP at temperature of 200°C. We have found that contrary to published information which recommends the concentration of polymer in solvent NMP as 200 gm/litre or more, the maximum concentration of polymer allowable in NMP is 80-150 gm/litre and more preferably 100-130 gm/litre. Operating the synthesis of PAEN at high dilution does not affect the economics of the process adversely as the solvent can be easily distilled and reused.
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We have also found surprisingly that the particle size of the base, Na2C03 used is also critical in maintaining the polymer is solution. The preferred particle size range is 10 microns to 120 microns and more preferably 30 microns to 100 microns.
Using the appropriate combination of the above two factors we have developed a process to manufacture PAEN possessing excellent mechanical and thermal properties . The invention will now be described in details.
Description of the invention:
As described in the prior art above, the available published processes for manufacture of PAEN use high concentrations of polymer during synthesis. This high concentration of polymer causes premature precipitation of the polymer from the solvent NMP at the temperature of polymerization of 190-200°C. Precipitated polymer chains will have free alkoxy groups and these free alkoxy groups which have not been endcapped/blocked are still "alive" and are active sites for further reaction with the result that polymer containing such free'alkoxy groups has a low thermal stability. To overcome this we have found that it is necessary to carry out the reaction at conditions of dilution such that the polymer is always in solution. The maximum allowable concentration of polymer is 80-150 gm/litre and it is even more preferred to have a concentration of 100-130 gm/litre. Though the increased dilution increases reaction times from 2-3 hours to 10-12 hours and even up to 30-35 hours depending on the amount of dilution, the polymer produced is found to be completely thermally stable and does not undergo degradation even after these long reaction times of even 30-35 hours. As has been reported in the prior art above, the polymers synthesized in the past have the problem of rapid degradation resulting in drop in viscosity due to low thermal stability. The NMP that is used for the polymerization process can be readily recycled and reused after the termination of the polymerization and the drowning of the reaction mass in a suitable solvent. The NMP is separated from this solvent by fractional distillation. As a result of extensive research we have also found that the polymerization process is greatly affected by the particle size of the base used, Na2C03 or K2CO3. The rate of
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polymerization depends on the particle size of the base, i.e. sodium carbonate/sodium bicarbonate or potassium carbonate used. Variation in the particle size of the base causes varying rates of polymerization. It has been observed that the polymerization reaction mass can become homogeneous/non-homogeneous, depending upon the particle size of the employed base. Homogeneous polymerization has generally been found to give a polymer of consistent thermal and mechanical properties, however, the same can not be obtained by non-homogeneous polymerization. The base used is sodium carbonate, sodium hydroxide, potassium hydroxide, sodium bicarbonate or potassium carbonate, preferably sodium carbonate. The particle size is adjusted by grinding, jet milling or any other methods known to those skilled in the art. The desired particle size ranges from 10 microns to 250 microns, preferably 30 microns to 200 microns. It is observed that particle size below this range results in rapid rate of reaction and premature precipitation of the polymer from the solvent. At the same time particle size above this range results in a sluggish rate of reaction and very long reaction times.
An additional factor influencing the molecular weight build up of the polymer is the stoichiometry of the reactants used. The reaction generally requires one mole of the dihydroxy benzene and 1 mole of dihalogeno benzonitrile. The desired molar stoichiometric ratio of the dihydroxy benzene to the dihalogeno benzonitirle is 1:1.1, preferably 1:1.05 and more preferably 1:1.005. A slight excess of the dihalogeno benzonitrile is preferred, to achieve better thermal and mechanical properties. The slight excess of the dihalogenobenzonitrile functions as an end blocking agent. If the quantity of the djhalogeno benzonitrile substantially exceeds the specified stoichiometry, it leads to a very long reaction time. If the dihalogeno benzonitrile is under added vis-a-vis the stoichiometric amount then the inherent viscosity builds up rapidly with attendant degradation.
The following examples illustrate the way in which the process of the invention may be carried out in practice. However it should be understood that the present invention is by no means restricted to the specific examples given below
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Embodiments:
Example 1:
110 gm of resorcinol, 1600 ml of N-methyl pyrrolidone, 1000 ml of toluene, 110 gm of sodium carbonate (75-150 micron size) , 141.5 gm of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. It is maintained at 200°C for 10 hrs. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer, 188.1 gm (yield = 90%) showed inherent viscosity 0.95 dl/gm.
Example 2:
110 gm of resorcinol, 1700 ml of N-methyl pyrrolidone, 1000 ml of toluene, 110 gm of sodium carbonate (75-150 micron size), 141 gm of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. It is maintained at 200°C for 6 hrs. The pH of the system was maintained at 9.2 to 9.5 by addition of sodium carbonate. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic, contamination. The isolated polymer, 186 gms (yield = 39%) showed inherent viscosity 0.9 dl/gm.
Comparative Example 1:
110 gm of resorcinol, 1000 ml of N-methyl pyrrolidone (corresponding to a polymer concentration of 209 gm/litre), 1000 ml of toluene, 110 gm of sodium carbonate (30-50 micron size, jet milled) , 141 gm of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. The polymer mass became a thick sludge which was not stirrable. After 4 hours the reaction was terminated and the polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics.
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Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination.. The isolated polymer showed inherent viscosity 0.6 dl/gm
Example 3 :
110 gm of resorcinol, 1400 ml of N-methyl pyrrolidone, 1000 ml of toluene, 110 gm of sodium carbonate (75-150 micron size) , 140.39 gm (corresponding to I.O Im/m) of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. It is maintained at 200°C for S hrs. The pH of the system was maintained at 9.2 to 9.5 by addition of sodium carbonate. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer, 188 gms (yield = 90%) showed inherent viscosity 0.95 dl/gm.
Example 4 :
110 gm of resorcinol, 1400 ml of N-methyl pyrrolidone, 1000 ml of toluene, 110 gm of sodium carbonate (75-150 micron size) , 144 gm (corresponding to 1.03 m/m) of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. It is maintained at 200°C for 20 hrs. The pH of the system was maintained at 9.2 to 9.5 by addition of sodium carbonate. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer, 192 gms (yield = 92%) showed inherent viscosity 0.97 dl/gm.
Comparative Example 2 :
44 gm of resorcinol, 560 ml of N-methyl pyrrolidone, 400 ml of toluene, 45 gm of
sodium carbonate (75-150 micron size) , 70 gm (corresponding to 1.015 m/m) of 2,6
dichloro benzonitrile are heated to 150°C. The system is dehydrated and temperature

is raised to 200°C. It is maintained at 204°C for 8 hrs. The pH of the system was maintained at 9.2 to 9.5 by addition of sodium carbonate. The polymer is isolated by
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drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer, 188 gins (yield = 90%) showed inherent viscosity 0.45 dl/gm.
Example 5 :
110 gm of resorcinol, 1000 ml of N,N-dimethyl imidazolidone, 500 ml of toluene, 110 gm of sodium carbonate (75-150 micron size) , 141 gm of 2,6-difluoro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C . The pH of the system is adjusted to 9.5 by addition of sodium carbonate. It is maintained at 200°C for 10 hrs. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer (yield = 90%) showed inherent viscosity 0.9 dl/gm.
Example 6 :
44 gm of hydroquinone, 560 ml of N-methyl pyrrolidone, 400 ml of toluene, 58 gm of potassium carbonate (100-250 micron size), 70 gm (corresponding to 1.015 m/m) of 2,6 dichloro benzonitrile are heated to 150°C. The system is dehydrated and temperature is raised to 200°C. It is maintained at 200°C for 4 hrs. The pH of the system was maintained at 9.2 to 9.5 by addition of potassium carbonate. The polymer is isolated by drowning the reaction mass in water and filtration of the mass. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination. The isolated polymer, 133 gms (yield = 90%) showed inherent viscositv 0.30 dl/qm.
Example 7
4400 gm of Resorcinol, 56 litre of N-methyl pyrrolidone, 40 litre of toluene, 4402 gm of sodium carbonate (75-150 microns ) & 5660 gm of 2,6-difluorobenzonitrile are heated to 150°C. The system is dehydrated and the temp is raised to 200°C. It is maintained
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for 7 hrs. The polymer is isolated by drowning the reaction mass in toluene and filtration followed by washing of the cake with methanol and subsequently with water. The polymer is refluxed with distilled water three times to remove inorganics. Subsequently it is treated with disodium salt of EDTA to remove all ionic metallic contamination.. The isolated polymer 7859 g (Yield = 94 % ) showed inherent viscosity 0.98 dl/g.
Dated 29th day of May 2008

Applicant
Satish B. Limaye Sr. Officer- Sci. Inf. & IPR Management. Gharda Chemicals Ltd.
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