Title of Invention	A PROCESS FOR PRODUCTION OF HIGH MOLECULAR WEIGHT, HIGH CHAR YIELDING ACRYLONITRILE POLYMER
Abstract	Describes a process for the production of high molecular weight (one million and above) acrylonitrile copolymers (PAN) capable of giving higher char yield which could be effectively used as a precursor resin for spinning special acrylic fibre for eventual conversion to carbon fibre with good carbon yield. Describes and ascertains the nature of this invention and the manner in which it is to be performed.

Title of Invention

A PROCESS FOR PRODUCTION OF HIGH MOLECULAR WEIGHT, HIGH CHAR YIELDING ACRYLONITRILE POLYMER

Abstract

Describes a process for the production of high molecular weight (one million and above) acrylonitrile copolymers (PAN) capable of giving higher char yield which could be effectively used as a precursor resin for spinning special acrylic fibre for eventual conversion to carbon fibre with good carbon yield. Describes and ascertains the nature of this invention and the manner in which it is to be performed.

Full Text	A PROCESS FOR PRODUCTION OF HIGH MOLECULAR WEIGHT, HIGH CHAR YIELDING ACRYLONITRILE COPOLYMER Field of the invention: This invention relates to the production of high molecular weight (one million and above) acrylonitrile copolymers (PAN) capable of giving higher char yield Description of the Prior Art: Carbon fibres have general widespread acceptance in high-tech composite area due to their low density, high strength, high stiffness, good resistance to chemical and environmental effects and excellent heat stability. Most widely adopted processes for carbon fibres are based on rayon, PAN and pitch as precursors. PAN based carbon fibre is preferred as it offers high/medium modulus in combination with good strength and strain capability [1]. Good quality carbon fibres are made from special acrylic fibres (SAF) prepared by copolymerising acrylonitrile with a small proportion of selected comonomers [2-6]. A large volume of literature, mostly patents, describes a multitude of methods for preparing SAF polymers. However, these literatures do not point to any unique method for its synthesis nor describe any unique characteristics for a precursor polymer. The general conclusion drawn from the vast patent literature is that the PAN polymers meant for carbon fibre are to possess generally the following properties. • High molar mass, of the order of-- 4 - 8x10 ^ • Appropriate polydispersity , 2-3 ? Broad exothermic decomposition temperature initiated at -'180-200°C. ? High carbon yield > 40% (900°C) Some experts' opinions sound that higher molar mass and narrow dispersity are conducive to good quality SAF polymer [6,7]. PAN homopolymer is known to yield poor carbon yield for the fibre. SAF from PAN copolymer containing a small percentage of selected comonomers yields superior carbon fibre. The comonomers play an important role in lowering the initiation temperature and slowing down the propagation step in the PAN copolymer during thermo-oxidative stabilization. Although patent literature suggests various comonomers, those containing carboxylic acids are known to play a noted role in achieving the required thermal characteristics for the S AF [8-11]. The acidic monomers lower the temperature of initiation of the cyclisation reaction, which is preferred to occur normally at around 180-200°C [12-14], The drop in initiation temperature is maximum for itaconic acid. Most of the literature cites a comonomer concentration in the broad range of 2-15%. The actual acid concentration and the copolymer composition are to be arrived at by the developing agency through characterization of the resultant polymer. A large number of acrylonitrile copolymers suitable as carbon fibre precursor have been reported. Bajaj etal, in a review article cites their overall characteristics and methods of realization [15]. Gupta etal has expanded the scope of such a review including further advances in acrylic copolymers suitable for carbon fibre. In several cases, the copolymer of choice is itaconic acid (lA) [16]. Some successful compositions contain an acrylic ester preferably methyl acrylate as the third comononer for increasing the tenacity of the SAF[17]. Earlier, the syntheses of these copolymers and terpolymers have been effected by polymerization of the monomers in inorganic solufions comprised of ZnCh or sodium thiocyanate [ 18-23]. In such cases, the polymer solution is directly used as the spinning dope and the molecular characteristics including composition and molecular weights of the formed polymer are rarely made known. In this case, the resin as well as the fibre incorporates a good amount of inorganic ions, which could have some detrimental effect on the carbonization phenomenon and quality of the resultant carbon fiber [24,25]. Several of the above patents divulge limited information on compositions of PAN suitable for SAP. However, none of them defines a unique composifion or molecular characteristics of the precursor resin. The general accepted concept is that a high modulus special acrylic fibre requires a high molecular weight precursor polymer. The high char yielding property of the precursor is mandatory for obtaining high yield of good quality carbon fiber at the final stage. Solution polymerization technique for their synthesis of such resins has some limitations for achieving very high molecular weight. Bulk polymerization is not preferred as it is difficult to control the highly exothermic reaction, particularly when the polymer is insoluble in the monomer. Ultra high mol wt PAN synthesis by suspension polymerization have been described in a prior art[ 26]. It is good for water treatment application only. Terpolymer containing methyl acrylate and itaconic acid with ultra high mol wt by suspension polymerisafion technique have also been described [17], However, its char properties are not described. Some reports cite emulsion polymerization technique for achieving high molecular weight PAN precursors [26-29]. Although this method is good for synthesis of homopolymers, it is not an advisable technique for copolymer synthesis. The reason is that during copolymerisation of two or more monomers, control of copolymer composition becomes difficult as the different monomers partition differently in the aqueous and organic phases. The situation is aggravated by the good solubility of AN in water (to the extent of 7%). In suspension polymerization involving water soluble monomers, the polymer composition will not be uniform throughout the reaction as the polymerization can proceed in both aqueous and organic phase and due to the partition of the various monomers between the two phases. In order to achieve lower cyclisation temperature and good char yield, it is imperative that the copolymer incorporates the acidic comonomer in a definite proportion. Control of the polymer composition is easier in homogeneous solution polymerization than in emulsion or suspension techniques. Compositional heterogeneity of the formed polymers are minimal in homogenous solution polymerization. Hence it is preferable to synthesize PAN precursor for carbon fibre by this technique. Generally, solution polymerization limits the polymer molecular weight. Normal homogenous polymerization in solution limits the polymer molecular weight due to the kinetic impositions of the lower monomer concentration and the chain transfer by the solvent. Attempts to increase molecular weight by performing polymerization in bulk ends up in insoluble polymers of acrylonitrile. Polymer synthesis by emulsion technique for the same objectives leads to compositionally heterogeneous polymers for reasons stated early. Synthesis of tractable PAN copolymer with a controlled composition possessing both high molar mass and high char yielding properties has not been the subject of any previous invention. Objects Of The Invention: The main objective of the present invention is to vent out a free radical solution process for production of very high molecular weight acrylonitrile-based copolymers and terpolymers of controlled composition, capable of undergoing cyclisation temperature at around 200^C and providing high char yield (>40%). The resin is suitable for spinning to special acrylic fibre for eventual conversion to carbon fibre. Description Of The Invention: The process: The acrylonitrile copolymer is made by free radical copolymerization of two (or optionally three) vinyl monomers in a solvent by a free radical process. One such monomer is acrylonitrile. The second monomer of the mixture is a vinyl acid constituted from among acrylic acid, methacrylic acid, vinyl sulphonic acid, butene dioic acid (itaconic acid) or their derivatives. The preferred comonomer is itaconic acid. The mixture can optionally contain a vinyl monomer from among acrylic acid ester of alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol or ethyl hexyl alcohol. Instead of acrylates the methacrylate esters of the above alcohols can also be used. The preferred monomer is methyl acrylate or ethyl acrylate. The free radical initiator used for polymerisation is one among the azo initiators typically azobis isobutyronitrile or azobiscyanocyclohexane. Peroxides such as benzoyl peroxide, ditertiary butyl peroxide, cyclohexanone peroxide and butyl hydroperoxide can also be used as polymerisation catalysts. The polymerisation is done in an organic solvent selected among dimethyl formamide (DMF) or dimethyl acetamide (DMAc), dimethyl solfoxide or their mixtures in any combination and proportions. Typically dimethyl sulfoxide can be chosen as the solvent. The solvent content can vary between 20-40 parts per 100 parts by weight of the total monomer. The polymerization is performed at temperatures between 50-90 '^C for 3 to 10 hours, the preferred temperature being 55-60°C. The formed polymer is swollen in the solvent and pure polymer is isolated by pouring a non-solvent to the reaction mixture under agitation that breaks the gel. The non-solvent can be chosen among alcohols, such as methanol, ethanol, isopropanol, butanol or a mixture of these in any combination and proportion. Typically, methanol can be chosen. The non-solvent can contain upto 50 vol % of water. The non-solvent composition can be 150-1000 parts per 100 parts of the total monomer, the preferred composition being 300 parts. In such a copolymer formulation, the acrylonitrile part can vary from 85-99% by weight, the vinyl acid monomer can vary between 1-15 % by weight and the vinyl monomer is varied from 1 to 15 % by weight. The free radical initiator is taken at a concentration ranging from 0.02 to 0.05 percent by weight of the total monomer. Optionally, the unreacted monomers, acrylonitrile and alkyl acrylate can be recovered from the spent by distillation. The high molecular weight is achieved by a control of monomer/initiator/solvent rapport. The cyclisation temperature and the char yield are achieved by the control of composition of the acid comonomer. The following examples illustrate typical details of synthesis of the copolymer. Fig. 1. TGA/DTA of acrylonitrile-co-itaconic acid copolymer Fig. 2. TGA/DTA of poly(acrylonitrile-co-methylacrylate-itaconic acidj Example 1, Process for synthesis of PAN copolymer 450 parts of acrylonitrile is mixed with 9 parts of itaconic acid in 100 parts of dimethyl formamide in a thermostated reactor. The system is de-aerated by purging argon through the solution for 15 min. The temperature is raised to 55°C while maintaining the system under argon and a solution containing 0.20 part of azobisisobutyronitnle in 10 parts of DMF is injected to the system. The reaction system is agitated through mechanical device for 4-6 hours. The polymer swollen by solvent precipitates in the system and is isolated by pouring 2000 parts of methanol under agitation to the gel. The white fine polymer powder is isolated by filtration and is further purified by Soxhelet extraction using methanol for 8-16 h. The polymer is then dried at 40 to 50^C under vacuum for 8 to 12 h. The yield of the polymer is 15-20%. It is characterized by intrinsic viscosity measurement in DMF solution at 25°C. Typically the intrinsic viscosity is 6-9 dL/g corresponding to an average molecular weight of 0.95 -1.5 million g/mole. The acid value of the polymer is 28-33 mg KOH/g. The polymer shows a cyclisation temperature initiated at 200°C and an anaerobic char residue of 40-55 at 900°C under differential thermal/ thermogravimetric analysis conditions at a heating rate of IC^C/min in argon. Figure 1 shows a typical thermogram of one such copolymer. The polymer is soluble in DMF, DMSO and the dope can be used for spinning fibre. Example 2. Process for synthesis of PAN terpolymer 450 parts of acrylonitrile and 19.5 parts methyl acrylate are mixed with 9 parts of itaconic acid in 150 parts of dimethyl sulfoxide in a thennostated reactor. The system is de-aerated by purging argon through the solution for 15 min. The temperature is raised to 55°C while maintaining the system under argon and a solution containing 0.20 part of azobisisobutyronitnle in 10 parts of DMSO is injected to the system. The reaction system is agitated through mechanical device for 6 hours. The polymer, swollen by solvent precipitates in the system and is isolated by pouring 2000 parts of methanol under agitation. The white fine powder is isolated by filtration and is further purified by Soxhelet extraction using methanol for 8-16 h. The polymer is then dried at 40 to 50°C under vacuum for 8 to 12 h. The yield of the polymer is 15-20%. It is characterized by intrinsic viscosity measurement in DMF solution at 25°C. Typically the intrinsic viscosity is 6-9 dL/g corresponding to an average molecular weight of 0.95 -1.5 million g/mole. The acid value of the polymer is 45-55 mg KOH/g. The nitrogen - content of the polymer is 16 to 23 %. The polymer shows a cyclisation temperature initiated at 200°C and an anaerobic char residue of 40-50% at 900°C under differential thermal/ thermogravimetric analysis conditions at a heating rate of 10°C/min in argon. Figure 2 shows a typical thermogram of one such terpolymer. The polymer is soluble in DMF, DMSO and the dope can be used for spinning fibre. 4.2 References: 1. Lee S. International Encyclopaedia of Composites; VCH: New York, 1990-91; Vol.1 2. Nikkiso Co. Ltd., Japan Kokai Tokkyo Koho 60,39,408 (1985); Chem. Abstr., 101(22), 80(1985) Abstr. 186605 3. T Koji, Sugaken, Japan Kokai Tokkyo Koho 49, 81, 628 (1974) 4. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63, 275, 715 (1988); Chem. Abstr., 110(8), 96 (1989) Abstr 59453 5. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63, 275, 716 (1988); Chem. Abstr., 110(8), 96 (1989), Abstr 59454 6. T Mikolajczyk, I Krucinska, M Kamecka Jedrzejczak. Text. Res. J., 59(9,10,11), 536 (1989) 7. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63,59,409 (1988); Chem. Abstr., 109(2), 69(1988) Abstr 7938 8. Mitsubishi Rayon Co., Ltd., Jpn. Kokai Tokkyo Koho, JP 62,276,014 (1987); Chem. Abstr., 108:152072.R2-35 9. Mitsubishi Rayon Co., Ltd., Jpn. Kokai Tokkyo Koho, JP 61,207,622 (1986); Chem. Abstr., 106(4):58(1987):19872,R1-117 10.US4,981,175 Daumit Gene P, Ko Yoon S, Slater Christopher R, Venner Jozef G, Young Chi C, Zwick Maurice M BASF Aktiengesellschaft March 26, 1990. 11. Mitsubishi Rayon Co., Ltd., Jpn. Kokai Tokkyo Koho, JP 05,295,621 (1994); Chem. Abstr., 120:136983.Kasaba Yukio, Nishida Koji, Makishima Toshihiro 12. Mitsubishi Rayon Co., Ltd., Jpn. Kokai Tokkyo Koho, JP 05,295,621 (1993); Chem. Abstr., 120:136983.R2-26 13. P Bajaj, D K Paliwal, A K Gupta. J Appl Polym Sci 49, 823-833, 1993 14. J R Ebdon, T N Huckerby, T C Hunter Polymer 35(2), 250-256, (1994) 15. P. Bajaj etal,J. Macromol Sci. Rev. Macrmol Chem. Phys., C31(l), 1-89(1991) 16. Gupta etal, J. Macromol Sci. Rev. Macrmol Chem. Phys., C36(l), 1-76 (1996) 17. C Zhang, R D Gilbert, R E Fomes. J. Appl. Polym. Sci. 58, 2067-2075 (1995) 18. Mah S, MaekawaT, Okamura S, J Macromol. Sci Chem, 1977, All, 687&705 19. MaekawaT, Okamura S, J Macromol. Sci Chem, 1976, AlO, 1565 20. V K Guev, M G Bol'shakova, 11 Dizer, VI Martynenko, A G Ovcharov, V P Reshetov, L 1 Smimova, O G Tarakonov and A D Lunev, USSR, SU 1,081,246 (1984); Chem. Abstr., 101:56436.R2-18/R1-106 21. Yu M Malyshev and B E Geller, Khim. Volokna, 3, 26(1985).R1-115 22. Nikkiso Co., Ltd., Eur. Pat. 178,890 (1986); Chem. Abstr., 105:99083.R2-12/R1-103 23. Toho Belson, Co. Ltd., Jpn. Kokai Tokkyo Koho, JP 61,119,720 (1986); Chem. Abstr., 106:68692.R2-14/R1-104 24. M K Ismail, Carbon, 25(5), 653(1987).R1-116, Mitsubishi Rayon Co., Ltd., Jpn Kokai Tokkyo Koho, JP 61,207,622 (1986) Chem. Abstr., 104(6), 76 (1986) 25. Mitsubishi Rayon Co., Ltd., Jpn. Kokai Tokkyo Koho, JP 60,167,931 (1985); Chem. Abstr., 104(6):78 (1986):35396.R1-118 26. US Patent 4,254,250 Glowaky; Raymond C. (Niantic, CT); Kurowsky; Steven R. (East Lyme, CT); Sysko; Robert J. (East Lyme, CT) Pfizer Inc. (New York, NY) 27. Kwon Young D, Kavesh Sheldon, Prevorsek Dusan C. Allied Signal Inc. US Patent 4,883,628 28. Hangquan Li 1, Zhongjie Du 1, Eli Ruckenstein, Journal of Applied Polymer Science 68, 999-1011, 1998 29. Ruckenstein and Li, Polymer Bull., 37, 43 (1996) I / We claim: 1. A process for the preparation of an acrylonitrile co-polymer by free radical copolymerization comprising steps of: a. polymerizing an acrylonitile monomer with one or more monomers in an organic solvent in presence of a free radical initiator in argon atmosphere under agitation to obtain a swollen polymer, b. adding a non-solvent to the swollen polymer of step (a), isolating fine powder of polymer by filtration, c. purifying and drying the polymer of step (b) to obtain high molecular weight acrylonitile co- polymer. 2. A process of claim 1, wherein monomer other than acrylonitile monomer is a vinyl monomer selected from a group consisting of vinyl acid and its derivatives thereof. 3. A process of claim 2, wherein the vinyl acid monomer is selected from a group consisting of acrylic acid, methacrylic acid, vinyl sulphonic acid and butane dioic acid (itaconic acid). 4. A process of claim 2, wherein the vinyl acid derivative monomer is an ester of vinylacid and an alcohol. 5. A process of claim 4, wherein the alcohol is selected from a group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol and ethyl hexyl alcohol 6. A process of claim 1, wherein the solvent used is selected from a group consisting of dimethyl formamide (DMF) or dimethyl acetamide ( DM Ac), dimethyl solfoxide and mixtures thereof. 7. A process of claim I, wherein the free radical initiator is selected from a group consisting of azobisisobutyronitrile, azobiscyanocyclohexane, benzoyl peroxide, di-tertiary butyl peroxide, cyclohexanone peroxide and butyl hydroperoxide. Preferably azobisisobutyronitrile 8. A process of claim 1, wherein concentration of free radical initiator is in the range of 0.02 to 0.05 percent by weight of the total monomer. 9. A process of clami 1, wherein the amount of solvent used is in the range of 20-40 parts per 100 parts by weight of the total monomer. 10. A process of claim 1, wherein the polymerization is performed at a temperature ranging between 50-90^C for 3 to 10 hours, preferably at a temperature ranging between 55-60X. 11. A process of claim 1, wherein the non-solvent is an alcohol selected from a group consisting of methanol, ethanol, isopropanol, butanol and mixtures thereof. 12. A process of claim 11, wherein the non-solvent may further comprise of up to 50 vol % of water. 13. A process of claim 1, wherein the non-solvent used is in the range between 150 and 1000 parts per 100 parts of total monomer and preferably 300 parts of total monomer 14. A process of claim 1, wherein acrylonitrile copolymer obtained comprises of acrylonitrile 85-99% by weight, vinyl acid monomer between 1-15 % by weight and vinyl acid monomer derivative from 0 to 15 % by weight. 15. A process of claim 1, wherein the acrylonitrile co-polymer of average molecular weight 0.9 to 1.5 million g/mole has an intrinsic viscosity of 6.0-9.0 dL/g in DMF at a temperature of 25^ C 16. A process of claim 1, wherein the acrylonitrile co-polymer of average molecular weight 0.9 to 1.5 million g/mole shows a cyclization temperature initiated at about 200°C and with an anaerobic char yield of 40-55% by weight at 900°C 17. That the acrylic copolymer as claimed in claims 1-16 can be spun in to a special acrylic fibre by dissolving the polymer in a solvent selected from DMF, DMSO or mixtures thereof

Full Text

A PROCESS FOR PRODUCTION OF HIGH MOLECULAR WEIGHT, HIGH CHAR
YIELDING ACRYLONITRILE COPOLYMER
Field of the invention:
This invention relates to the production of high molecular weight (one million and above) acrylonitrile copolymers (PAN) capable of giving higher char yield
Description of the Prior Art:
Carbon fibres have general widespread acceptance in high-tech composite area due to their low density, high strength, high stiffness, good resistance to chemical and environmental effects and excellent heat stability. Most widely adopted processes for carbon fibres are based on rayon, PAN and pitch as precursors. PAN based carbon fibre is preferred as it offers high/medium modulus in combination with good strength and strain capability [1]. Good quality carbon fibres are made from special acrylic fibres (SAF) prepared by copolymerising acrylonitrile with a small proportion of selected comonomers [2-6]. A large volume of literature, mostly patents, describes a multitude of methods for preparing SAF polymers. However, these literatures do not point to any unique method for its synthesis nor describe any unique characteristics for a precursor polymer. The general conclusion drawn from the vast patent literature is that the PAN polymers meant for carbon fibre are to possess generally the following properties.
• High molar mass, of the order of-- 4 - 8x10 ^
• Appropriate polydispersity , 2-3

? Broad exothermic decomposition temperature initiated at -'180-200°C.
? High carbon yield > 40% (900°C)
Some experts' opinions sound that higher molar mass and narrow dispersity are conducive to good quality SAF polymer [6,7]. PAN homopolymer is known to yield poor carbon yield for the fibre. SAF from PAN copolymer containing a small percentage of selected comonomers yields superior carbon fibre. The comonomers play an important role in lowering the initiation temperature and slowing down the propagation step in the PAN copolymer during thermo-oxidative stabilization. Although patent literature suggests various comonomers, those

containing carboxylic acids are known to play a noted role in achieving the required thermal characteristics for the S AF [8-11]. The acidic monomers lower the temperature of initiation of the cyclisation reaction, which is preferred to occur normally at around 180-200°C [12-14], The drop in initiation temperature is maximum for itaconic acid. Most of the literature cites a comonomer concentration in the broad range of 2-15%. The actual acid concentration and the copolymer composition are to be arrived at by the developing agency through characterization of the resultant polymer.
A large number of acrylonitrile copolymers suitable as carbon fibre precursor have been reported. Bajaj etal, in a review article cites their overall characteristics and methods of realization [15]. Gupta etal has expanded the scope of such a review including further advances in acrylic copolymers suitable for carbon fibre. In several cases, the copolymer of choice is itaconic acid (lA) [16]. Some successful compositions contain an acrylic ester preferably methyl acrylate as the third comononer for increasing the tenacity of the SAF[17]. Earlier, the syntheses of these copolymers and terpolymers have been effected by polymerization of the monomers in inorganic solufions comprised of ZnCh or sodium thiocyanate [ 18-23]. In such cases, the polymer solution is directly used as the spinning dope and the molecular characteristics including composition and molecular weights of the formed polymer are rarely made known. In this case, the resin as well as the fibre incorporates a good amount of inorganic ions, which could have some detrimental effect on the carbonization phenomenon and quality of the resultant carbon fiber [24,25]. Several of the above patents divulge limited information on compositions of PAN suitable for SAP. However, none of them defines a unique composifion or molecular characteristics of the precursor resin.
The general accepted concept is that a high modulus special acrylic fibre requires a high molecular weight precursor polymer. The high char yielding property of the precursor is mandatory for obtaining high yield of good quality carbon fiber at the final stage. Solution polymerization technique for their synthesis of such resins has some limitations for achieving very high molecular weight. Bulk polymerization is not preferred as it is difficult to control the highly exothermic reaction, particularly when the polymer is insoluble in the monomer. Ultra high mol wt PAN synthesis by suspension polymerization have been described in a prior art[ 26]. It is good for water treatment application only. Terpolymer containing methyl acrylate and itaconic acid with ultra high mol wt by suspension polymerisafion technique have also been described [17], However, its char properties are not described. Some reports cite emulsion

polymerization technique for achieving high molecular weight PAN precursors [26-29]. Although this method is good for synthesis of homopolymers, it is not an advisable technique for copolymer synthesis. The reason is that during copolymerisation of two or more monomers, control of copolymer composition becomes difficult as the different monomers partition differently in the aqueous and organic phases. The situation is aggravated by the good solubility of AN in water (to the extent of 7%). In suspension polymerization involving water soluble monomers, the polymer composition will not be uniform throughout the reaction as the polymerization can proceed in both aqueous and organic phase and due to the partition of the various monomers between the two phases. In order to achieve lower cyclisation temperature and good char yield, it is imperative that the copolymer incorporates the acidic comonomer in a definite proportion. Control of the polymer composition is easier in homogeneous solution polymerization than in emulsion or suspension techniques. Compositional heterogeneity of the formed polymers are minimal in homogenous solution polymerization. Hence it is preferable to synthesize PAN precursor for carbon fibre by this technique. Generally, solution polymerization limits the polymer molecular weight. Normal homogenous polymerization in solution limits the polymer molecular weight due to the kinetic impositions of the lower monomer concentration and the chain transfer by the solvent. Attempts to increase molecular weight by performing polymerization in bulk ends up in insoluble polymers of acrylonitrile. Polymer synthesis by emulsion technique for the same objectives leads to compositionally heterogeneous polymers for reasons stated early. Synthesis of tractable PAN copolymer with a controlled composition possessing both high molar mass and high char yielding properties has not been the subject of any previous invention.
Objects Of The Invention:
The main objective of the present invention is to vent out a free radical solution process for production of very high molecular weight acrylonitrile-based copolymers and terpolymers of controlled composition, capable of undergoing cyclisation temperature at around 200^C and providing high char yield (>40%). The resin is suitable for spinning to special acrylic fibre for eventual conversion to carbon fibre.
Description Of The Invention: The process:
The acrylonitrile copolymer is made by free radical copolymerization of two (or optionally three)

vinyl monomers in a solvent by a free radical process. One such monomer is acrylonitrile. The second monomer of the mixture is a vinyl acid constituted from among acrylic acid, methacrylic acid, vinyl sulphonic acid, butene dioic acid (itaconic acid) or their derivatives. The preferred comonomer is itaconic acid. The mixture can optionally contain a vinyl monomer from among acrylic acid ester of alcohols such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol or ethyl hexyl alcohol. Instead of acrylates the methacrylate esters of the above alcohols can also be used. The preferred monomer is methyl acrylate or ethyl acrylate. The free radical initiator used for polymerisation is one among the azo initiators typically azobis isobutyronitrile or azobiscyanocyclohexane. Peroxides such as benzoyl peroxide, ditertiary butyl peroxide, cyclohexanone peroxide and butyl hydroperoxide can also be used as polymerisation catalysts. The polymerisation is done in an organic solvent selected among dimethyl formamide (DMF) or dimethyl acetamide (DMAc), dimethyl solfoxide or their mixtures in any combination and proportions. Typically dimethyl sulfoxide can be chosen as the solvent. The solvent content can vary between 20-40 parts per 100 parts by weight of the total monomer. The polymerization is performed at temperatures between 50-90 '^C for 3 to 10 hours, the preferred temperature being 55-60°C. The formed polymer is swollen in the solvent and pure polymer is isolated by pouring a non-solvent to the reaction mixture under agitation that breaks the gel. The non-solvent can be chosen among alcohols, such as methanol, ethanol, isopropanol, butanol or a mixture of these in any combination and proportion. Typically, methanol can be chosen. The non-solvent can contain upto 50 vol % of water. The non-solvent composition can be 150-1000 parts per 100 parts of the total monomer, the preferred composition being 300 parts. In such a copolymer formulation, the acrylonitrile part can vary from 85-99% by weight, the vinyl acid monomer can vary between 1-15 % by weight and the vinyl monomer is varied from 1 to 15 % by weight. The free radical initiator is taken at a concentration ranging from 0.02 to 0.05 percent by weight of the total monomer. Optionally, the unreacted monomers, acrylonitrile and alkyl acrylate can be recovered from the spent by distillation.
The high molecular weight is achieved by a control of monomer/initiator/solvent rapport. The cyclisation temperature and the char yield are achieved by the control of composition of the acid comonomer.
The following examples illustrate typical details of synthesis of the copolymer.
Fig. 1. TGA/DTA of acrylonitrile-co-itaconic acid copolymer

Fig. 2. TGA/DTA of poly(acrylonitrile-co-methylacrylate-itaconic acidj
Example 1, Process for synthesis of PAN copolymer
450 parts of acrylonitrile is mixed with 9 parts of itaconic acid in 100 parts of dimethyl formamide in a thermostated reactor. The system is de-aerated by purging argon through the solution for 15 min. The temperature is raised to 55°C while maintaining the system under argon and a solution containing 0.20 part of azobisisobutyronitnle in 10 parts of DMF is injected to the system. The reaction system is agitated through mechanical device for 4-6 hours. The polymer swollen by solvent precipitates in the system and is isolated by pouring 2000 parts of methanol under agitation to the gel. The white fine polymer powder is isolated by filtration and is further purified by Soxhelet extraction using methanol for 8-16 h. The polymer is then dried at 40 to 50*^C under vacuum for 8 to 12 h. The yield of the polymer is 15-20%. It is characterized by intrinsic viscosity measurement in DMF solution at 25°C. Typically the intrinsic viscosity is 6-9 dL/g corresponding to an average molecular weight of 0.95 -1.5 million g/mole. The acid value of the polymer is 28-33 mg KOH/g. The polymer shows a cyclisation temperature initiated at 200°C and an anaerobic char residue of 40-55 at 900°C under differential thermal/ thermogravimetric analysis conditions at a heating rate of IC^C/min in argon. Figure 1 shows a typical thermogram of one such copolymer. The polymer is soluble in DMF, DMSO and the dope can be used for spinning fibre.
Example 2. Process for synthesis of PAN terpolymer
450 parts of acrylonitrile and 19.5 parts methyl acrylate are mixed with 9 parts of itaconic acid in 150 parts of dimethyl sulfoxide in a thennostated reactor. The system is de-aerated by purging argon through the solution for 15 min. The temperature is raised to 55°C while maintaining the system under argon and a solution containing 0.20 part of azobisisobutyronitnle in 10 parts of DMSO is injected to the system. The reaction system is agitated through mechanical device for 6 hours. The polymer, swollen by solvent precipitates in the system and is isolated by pouring 2000 parts of methanol under agitation. The white fine powder is isolated by filtration and is further purified by Soxhelet extraction using methanol for 8-16 h. The polymer is then dried at 40 to 50°C under vacuum for 8 to 12 h. The yield of the polymer is 15-20%. It is characterized by intrinsic viscosity measurement in DMF solution at 25°C. Typically the intrinsic viscosity is 6-9 dL/g corresponding to an average molecular weight of 0.95 -1.5 million g/mole. The acid value

of the polymer is 45-55 mg KOH/g. The nitrogen - content of the polymer is 16 to 23 %. The polymer shows a cyclisation temperature initiated at 200°C and an anaerobic char residue of 40-50% at 900°C under differential thermal/ thermogravimetric analysis conditions at a heating rate of 10°C/min in argon. Figure 2 shows a typical thermogram of one such terpolymer. The polymer is soluble in DMF, DMSO and the dope can be used for spinning fibre.
4.2 References:
1. Lee S. International Encyclopaedia of Composites; VCH: New York, 1990-91; Vol.1
2. Nikkiso Co. Ltd., Japan Kokai Tokkyo Koho 60,39,408 (1985); Chem. Abstr., 101(22), 80(1985) Abstr. 186605
3. T Koji, Sugaken, Japan Kokai Tokkyo Koho 49, 81, 628 (1974)
4. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63, 275, 715 (1988); Chem. Abstr., 110(8), 96 (1989) Abstr 59453
5. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63, 275, 716 (1988); Chem. Abstr., 110(8), 96 (1989), Abstr 59454
6. T Mikolajczyk, I Krucinska, M Kamecka Jedrzejczak. Text. Res. J., 59(9,10,11), 536 (1989)
7. Mitsubishi Rayon Co. Ltd., Japan Kokai Tokkyo Koho 63,59,409 (1988); Chem. Abstr.,
109(2), 69(1988) Abstr 7938
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I / We claim:
1. A process for the preparation of an acrylonitrile co-polymer by free radical
copolymerization comprising steps of:
a. polymerizing an acrylonitile monomer with one or more monomers in an organic
solvent in presence of a free radical initiator in argon atmosphere under agitation
to obtain a swollen polymer,
b. adding a non-solvent to the swollen polymer of step (a), isolating fine powder of
polymer by filtration,
c. purifying and drying the polymer of step (b) to obtain high molecular weight
acrylonitile co- polymer.
2. A process of claim 1, wherein monomer other than acrylonitile monomer is a vinyl monomer selected from a group consisting of vinyl acid and its derivatives thereof.
3. A process of claim 2, wherein the vinyl acid monomer is selected from a group consisting of acrylic acid, methacrylic acid, vinyl sulphonic acid and butane dioic acid (itaconic acid).
4. A process of claim 2, wherein the vinyl acid derivative monomer is an ester of vinylacid and an alcohol.
5. A process of claim 4, wherein the alcohol is selected from a group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentanol, isopentanol and ethyl hexyl alcohol
6. A process of claim 1, wherein the solvent used is selected from a group consisting of dimethyl formamide (DMF) or dimethyl acetamide ( DM Ac), dimethyl solfoxide and mixtures thereof.
7. A process of claim I, wherein the free radical initiator is selected from a group consisting of azobisisobutyronitrile, azobiscyanocyclohexane, benzoyl peroxide, di-tertiary butyl peroxide, cyclohexanone peroxide and butyl hydroperoxide. Preferably azobisisobutyronitrile
8. A process of claim 1, wherein concentration of free radical initiator is in the range of 0.02

to 0.05 percent by weight of the total monomer.
9. A process of clami 1, wherein the amount of solvent used is in the range of 20-40 parts
per 100 parts by weight of the total monomer.
10. A process of claim 1, wherein the polymerization is performed at a temperature ranging
between 50-90^C for 3 to 10 hours, preferably at a temperature ranging between 55-60X.
11. A process of claim 1, wherein the non-solvent is an alcohol selected from a group
consisting of methanol, ethanol, isopropanol, butanol and mixtures thereof.
12. A process of claim 11, wherein the non-solvent may further comprise of up to 50 vol %
of water.
13. A process of claim 1, wherein the non-solvent used is in the range between 150 and 1000
parts per 100 parts of total monomer and preferably 300 parts of total monomer
14. A process of claim 1, wherein acrylonitrile copolymer obtained comprises of acrylonitrile
85-99% by weight, vinyl acid monomer between 1-15 % by weight and vinyl acid
monomer derivative from 0 to 15 % by weight.
15. A process of claim 1, wherein the acrylonitrile co-polymer of average molecular weight
0.9 to 1.5 million g/mole has an intrinsic viscosity of 6.0-9.0 dL/g in DMF at a
temperature of 25*^ C
16. A process of claim 1, wherein the acrylonitrile co-polymer of average molecular weight
0.9 to 1.5 million g/mole shows a cyclization temperature initiated at about 200°C and
with an anaerobic char yield of 40-55% by weight at 900°C
17. That the acrylic copolymer as claimed in claims 1-16 can be spun in to a special
acrylic fibre by dissolving the polymer in a solvent selected from DMF, DMSO or
mixtures thereof

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Patent Number

268886

Indian Patent Application Number

610/CHE/2004

PG Journal Number

39/2015

Publication Date

25-Sep-2015

Grant Date

21-Sep-2015

Date of Filing

24-Jun-2004

Name of Patentee

DEPARTMENT OF SPACE

Applicant Address

INDIAN SPACE RESEARCH ORGANISATION (ISRO) HEADQUARTERS, ANTARIKSH BHAVAN, NEW B.E.L ROAD, BANGALORE 560 094, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	CHETHRAPPILLY PADMANABHAN REGHUNADHAN NAIR	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA
2	PARAMESWARAN SIVADASAN	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA
3	VELOO SASEENDRAN	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA
4	BENNY KATTIKANAL GEORGE	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA
5	RENJITH DEVASIA	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA
6	KOVOOR NINAN NINAN	VIKRAM SARABHAI SPACE CENTRE INDIAN SPACE RESEARCH ORGANISATION (ISRO) THIRUVANANTHPURAM KERALA 695 022 INDIA

PCT International Classification Number

C08F 2/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA