POLYMERIZATION METHOD AND PRODUCT

Abstract

Methods of preparing a polyaniline homopolymer or copolymer comprising at least one carboxylic acid group, and homopolymers or copolymers arising therefrom, the methods comprising: preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group (eg. 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid) in a solvent selected from aqueous methanesulfonic acid or aqueous ammonia and optionally one or more additional polyaniline precursors (such as aniline); and oxidatively polymerising the polyaniline precursor or precursors.

Description

TECHNICAL FIELD

[0001] The invention relates to processes for preparing polymers that include aminobenzoic acid monomers, and to copolymers and homopolymers prepared by those processes.

BACKGROUND ART

[0002] Polymers of aniline and its derivatives are useful as antimicrobial agents and have good antistatic and free radical scavenging properties. These properties make them useful for the manufacture of antimicrobial, antistatic and antioxidant objects, and suitable for use in, for example, the health, food, packaging, water, paint, wood, textile, poultry, glass, paper, rubber, ceramic, seafood, sports, plastic and agricultural industries.

[0003] Adding substituents to polyaniline (PANI) is one way in which the various properties of the polymer can be improved. However, the synthesis of substituted PANIs is not always a straightforward matter. Any substituent introduced to the aniline building block needs to be compatible with the reagents used, which is not always possible under the traditionally robust oxidative polymerisation conditions used to form PANIs.

[0004] Carboxylated PANIs are one type of PANT derivative of particular interest due to their good antibacterial properties. Carboxylated PANIs can either be homopolymers, which could also be described as a poly(aminobenzoic acid) (poly ABAs) or copolymers, which could be considered as a PANT backbone bearing carboxylic acid groups on some of the aromatic rings. The probable structure of poly(2-aminobenzoic acid) and poly(3-aminobenzoic acid) (top) and the probable structure of copolymers of aniline and 2-aminobenzoic acid or 3-aminobenzoic acid (bottom), where X and Y are the numbers of repeat units are shown below.

##STR00001##

[0005] However, producing PANI homopolymers and copolymers from aminobenzoic acid (ABA) monomers in good yield and purity is not a simple procedure. There are significant problems with the solubilities of ABAs. ABAs tend to be solids, unlike aniline itself or many substituted anilines (alkyl anilines like toluidine, alkoxy anilines like anisidine etc) which can be used directly in their liquid form. This low solubility impacts upon the cost of synthesis and the quality of the resultant polymers.

[0006] There thus exists a need to produce poly-ABAs (carboxylated PANis) in high yield and in a cost effective manner, with high conversion of monomer units, short production time and high molecular weights.

[0007] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

SUMMARY

[0008] In a broad aspect, the invention provides a method of preparing a polyaniline homopolymer or copolymer comprising at least one carboxylic acid group; the method comprising:

preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in a solvent selected from aqueous methanesulfonic acid or aqueous ammonia and optionally one or more additional polyaniline precursors; and oxidatively polymerising the polyaniline precursor or precursors.

[0009] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

[0010] In one aspect, the invention provides a method of preparing a polyaniline homopolymer comprising carboxylic acid groups; the method comprising:

preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous methanesulfonic acid; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group.

[0011] In one aspect, the invention provides a method of preparing a polyaniline homopolymer comprising carboxylic acid groups; the method comprising:

preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous ammonia; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group.

[0012] The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group may be any aromatic ring bearing --NH.sub.2 and --COOH moieties in any position, with or without other substituents. In certain preferred embodiments, the substance being polymerised is selected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid.

[0013] Monomers other than amino benzoic acids can be used, for example aniline or pyrrole, or derivatives thereof may be used.

[0014] In one aspect, the invention provides a method of preparing a polyaniline copolymer comprising at least one carboxylic acid group; the method comprising:

preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous methanesulfonic acid and one or more additional polyaniline precursors; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group and the one or more additional polyaniline precursors.

[0015] In one aspect, the invention provides a method of preparing a polyaniline copolymer comprising at least one carboxylic acid group; the method comprising:

preparing a solution of a polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in aqueous ammonia and one or more additional polyaniline precursors; and oxidatively polymerising the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group and the one or more additional polyaniline precursors.

[0016] The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group may be any aromatic ring bearing --NH.sub.2 and --COOH moieties in any position, with or without other substituents. In certain preferred embodiments, the substance being polymerised is selected from 2-aminobenzoic acid, 3-aminobenzoic acid or 4-aminobenzoic acid. The one or more additional polyaniline precursors may be any amino substituted aromatic ring, which is in some cases preferably comprises aniline.

[0017] A possible structure of poly(4-aminobenzoic acid) is shown below.

##STR00002##

Monomers other than aminobenzoic acids can be used, for example aniline and other derivatives thereof or pyrrole and derivatives thereof may be used.

[0018] The most preferred copolymers are those formed from mixtures of aniline and 2-aminobenzoic acid, aniline and 3-aminobenzoic acid or aniline and 4-aminobenzoic acid. The possible structure of copolymers of aniline and 4-aminobenzoic Acid is shown below. Y and Z are the numbers of repeat units.

##STR00003##

[0019] The ratio of the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group: the one or more additional polyaniline precursors is from 99:1 to 1:99. Alternatively, ratios in the range 72:25 to 25:75 may be used.

[0020] If aqueous methane sulfonic acid is used, it is preferably in a concentration of 0.1 to 10 M in water. It is generally preferred if the ratio of concentration of ABA to methanesulfonic acid is from 2:1 to 1:2. For example, it is preferred to use a solution of methanesulfonic acid of around 1 M and an ABA concentration of around 0.5 M.

[0021] The polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group is preferably dissolved in the aqueous methane sulfonic acid and oxidising agent is added. If a copolymer is desired, additional polyaniline precursors may be added in a suitable compatible solvent, which may include water or aqueous methane sulfonic acid.

[0022] If ammonia is used, the polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group is suspended in water and ammonia is added to dissolve it. The amount and concentration required can be readily determined. Typically, commercial strength ammonia is added to a suspension of the ABA in water until the monomer is dissolved. The pH is readily maintained at around neutral to slightly alkaline pHs, for example around pH 7-8.

[0023] The reaction of aminobenzoic acid and/or aniline to synthesize the homopolymer or copolymer is carried out in an acidic or near neutral medium in the presence of an oxidizing agent. Any suitable oxidizing agent may be used. Suitable oxidizing agents include, although are not limited to ammonium persulphate, potassium ferricyanide, potassium iodate, hydrogen peroxide, cerium (IV) sulphate, potassium dichromate and sodium vanadate. For neutral/alkaline based reaction, preferably the oxidizing agent is ammonium persulphate or hydrogen peroxide.

[0024] The methods of the present invention will also usually further include the step of collecting the precipitated poly aminobenzoic acid homopolymer or copolymer by filtration.

DESCRIPTION

[0025] Aminobenzoic acids have low solubility in water and in common acids used to carry out oxidative polymerization. For example, 3-ABA has only around 5 wt % solubility in 1 M HCl, which is typical for ABAs generally. Even if the aminobenzoic acids can be dissolved to some extent, it is difficult to get them into solution at sufficiently high concentrations to achieve good yields of the resultant polyaniline polymer or copolymer. The present inventors have developed solvent systems based around methanesulfonic acid or ammonia that enable the monomer to be dissolved in MSA or ammonia at high concentration (15% by weight or higher)

[0026] The methods of the present invention enable the practical large scale production of PANIs, particularly those starting from amino benzoic acid derivatives, at room temperature. Because of the good solubility of the starting monomers, the reaction yield and starting monomer consumption is high and the reaction time is reduced, resulting in a less wasteful and more economic synthesis. Moreover, the products of the present invention have been found to have high molecular weight and, where copolymers are concerned, high incorporation of n-ABA in the resultant copolymer is observed.

COMPARATIVE EXAMPLES

[0027] Oxidative polymerisation of 3-amino benzoic acid to the corresponding polycarboxylated PANI was carried out under standard conditions using 1M HCl as monomer solvent and APS as oxidant.

[0028] From 150 ml 1 M HCl solution containing 2.2 g (16 mmol) 3-ABA, 0.0154 g polymer was obtained (0.7% yield*) when the reaction was performed at 10.degree. C. for 7 days

[0029] From 200 g 1 M HCl solution containing 10 g n-ABA monomer, 1 g polymer was obtained (10% yield*), when the reaction was performed at room temperature for 48 h

*Yield:=100.times.[mass of the polymer]/[mass of the (co)monomer(s)]

INVENTIVE EXAMPLES

Methane Sulfonic Acid as Solvent

[0030] Poly(n-amino benzoic acid) homopolymers, where n=2, 3 or 4 (P(n-ABA)) and poly(n-amino benzoic acid-co-aniline) copolymers (P(n-ABA-co-Ani)) were synthesised in 1 M methane sulfonic acid (MSA) at 25.degree. C. (ambient temperature), with ammonium persulfate (APS) as the oxidizing agent. The monomer(s) concentration and the mole ratio of monomer(s) to APS were kept constant at 0.5 M and 1:1.25 respectively. The mole ratio of n-aminobenzoic acid (n-ABA) to aniline (Ani) in the comonomer mixtures was varied from 99:1 to 1:99, or more usually 75:25 to 25:75.

[0031] The maximum concentration of n-aminobenzoic acid (n-ABA) in 1 M MSA is about 15%, which may be higher in more concentrated MSA.

Homopolymers

[0032] Homopolymers of the present invention can be designated as follows:

HpMn: Hp=Homopolymer, M=methane sulfonic acid (MSA), n=position of --COOH functional group (4 or 3 or 2) in n-ABA precursor. HpAn: Hp=Homopolymer, A=ammonia, n=position of --COOH functional group (4 or 3 or 2) in n-ABA precursor.

[0033] Synthesis of PANI homopolymers of aminobenzoic acids P(n-ABA): 13.86 g of 4-ABA was dissolved in 100 mL of 1 M MSA. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50.degree. C. From this process 7.2 g polymer HpM4 was obtained (52% yield).

[0034] The yield can be seen to be significantly better than that obtained from the use of HCl as solvent.

[0035] The use of 3-ABA and 2-ABA in an identical manner resulted in the synthesis of a homopolymer of 3-aminobenzoic HpM3 and a homopolymer of 2-aminobenzoic acid HpM2 respectively.

[0036] Table 1 shows the properties of HpMn homopolymers synthesised using MSA as solvent. The yields are significantly better than using traditional solvents, such as HCl.

TABLE-US-00001 TABLE 1 Antimicrobial property Free radical (Minimum inhibitory scavenging concentration) % (.mu.mol DPPH Yield Mol wt. Gram +ve Gram -ve scavenged/mg Conductivity Material Monomer Colour (%) (g/mol) (S. aureus) (E. coli) of sample) % (S/cm) HpM4 4ABA Dark 52 19826 0.5 1 64 <10.sup.-5 brown HpM3 3ABA Dark 18 12947 1 >2% 60 <10.sup.-3 brown HpM2 2ABA Dark 30 22200 0.25 1 61 <10.sup.-5 brown

Copolymers

[0037] Copolymers of the present invention can be designated as follows:

CpMnYZ: Cp=Copolymer, M=methane sulfonic acid (MSA), n=position of --COOH functional group (4 or 3 or 2) in n-ABA precursor, YZ ratio Y:Z of n-ABA:aniline in feed. CpAnYZ: Cp=Copolymer, A=ammonia, n=position of --COOH functional group (4 or 3 or 2) in n-ABA precursor, YZ ratio Y:Z of n-ABA:aniline in feed.

[0038] Synthesis of copolymers of aminobenzoic acids and aniline P(n-ABA-co-Ani): For a typical synthesis of P(n-ABA-co-Ani) (starting from a solution with equimolar proportions of comonomers, for example), 6.94 g of n-ABA was dissolved in 100 mL of 1 M MSA. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the solution of the monomers with constant stirring. Polymerisation was continued with stirring for 24 h. The polymer product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50.degree. C.

[0039] Oxidative synthesis of copolymer CpM411: 6.94 g of 4-ABA was dissolved in 100 mL of 1 M MSA. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 100 mL of water and added dropwise to the solution of the monomers with constant stirring. Polymerisation was continued with stirring for 24 h. The polymer product that precipitated from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50.degree. C. From this process 11.6 g copolymer (CpM411) was obtained (100% yield).

[0040] Under similar conditions, copolymers of 4-ABA and aniline, copolymers of 3-ABA and aniline, copolymers of 2-ABA and aniline at various monomer feed ratio (from 99:1 to 1:99) can be synthesized.

[0041] Table 2 shows the properties of copolymers (CpMnYZ) synthesised in acidic medium.

TABLE-US-00002 TABLE 2 Free radical Antimicrobial property scavenging (Minimum inhibitory (micromoles concentration) % of DPPH Monomer ratio Yield Gram +ve Gram -ve scavenged/mg Conductivity Material (n-ABA:Aniline) Colour (%) (S. aureus) (E. coli) of sample) % (S/cm) CpM431 4ABA:Aniline (3:1) Dark 78 0.25 2 57 <10.sup.-5 brown CpM411 4ABA:Aniline (1:1) Dark 100 0.5 >2 59 0.002 brown CpM413 4ABA:Aniline (1:3) Dark 112 0.5 >2 60 1 green CpM331 3ABA:Aniline (3:1) Dark 85 0.5 2 57 <10.sup.-5 brown CpM311 3ABA:Aniline (1:1) Dark 101 2 >2 54 0.002 brown CpM313 3ABA:Aniline (1:3) Dark 114 >2 >2 46 0.6 green CpM231 2ABA:Aniline (3:1) Dark 78 0.5 2 54 <10.sup.-5 brown CpM211 2ABA:Aniline (1:1) Dark 81 0.5 >2 47 0.04 brown CpM213 2ABA:Aniline (1:3) Dark 121 0.5 >2 54 2 green

Ammonia as Solvent

Homopolymers

[0042] Synthesis of HpA4 in non-acidic medium (by neutralizing monomer with ammonia): 13.86 g monomer (4-ABA) was dissolved in 100 mL water by neutralizing with 7.5 mL of 28% ammonia. 28.52 g of APS was dissolved in 92.5 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated out from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50.degree. C. From this process 11.37 g polymer HpA4 was obtained (82% yield).

[0043] Again, the yield can be seen to be significantly better than that obtained from the use of HCl as solvent. Under the same conditions HpA3 and HpA2 can be synthesized in non-acidic medium (by neutralizing monomer with ammonia.)

[0044] A possible reaction scheme for synthesis of poly(4-aminobenzoic acid) is shown below.

##STR00004##

[0045] Table 3 shows the properties of HpAn homopolymers synthesised by pre-neutralization with ammonia

TABLE-US-00003 TABLE 3 Free radical Antimicrobial property scavenging (Minimum inhibitory (.mu.mol concentration % DPPH Yield Mol wt Gram +ve Gram -ve scavenged/mg Conductivity Material Monomer Colour (%) (g/mol) (S. aureus) (E. coli) of sample) % (S/cm) HPA4 4ABA Dark 82 18362 0.125 >2 55 <10.sup.-3 brown HPA3 3ABA Dark 82 62847 1 2 61 <10.sup.-5 brown HPA2 2ABA Dark 71 44645 0.5 1 56 <10.sup.-5 brown

Copolymers

[0046] Oxidative synthesis of copolymer CpA411: 6.94 g monomer (4-ABA) was dissolved in 100 mL water by neutralizing with 4 mL of 28% ammonia. 4.66 g aniline was added to this solution and stirred for 15 mins. 28.52 g of APS was dissolved in 96 mL of water and added dropwise to the monomer solution with constant stirring. Polymerisation was continued with stirring for 24 h. The polymeric product that precipitated out from the solution was collected by filtration, washed thoroughly with distilled water then (vacuum) dried at 50.degree. C. From this process 10.2 g copolymer (CpA411) was obtained (88% yield).

[0047] Under similar conditions, copolymers of (4-ABA) and aniline, (3-ABA) and aniline, and (2-ABA) and aniline at various monomer feed ratio (can be from 99:1 to 1:99) can be synthesized in acidic medium.

[0048] Table 4 shows a property chart of copolymers (CpAnYZ) synthesised by pre-neutralization of monomer n-ABA with ammonia

TABLE-US-00004 TABLE 4 Free radical Antimicrobial property scavenging (Minimum inhibitory (micromoles concentration) % of DPPH Monomer ratio Yield Gram +ve Gram -ve scavenged/mg Conductivity Material (n-ABA:Aniline) Colour (%) (S aureus) (E. coli) of sample) % (S/cm) CpA431 4ABA:Aniline (3:1) Dark 83 0.06% >2% 60 <10.sup.-5 brown CpA411 4ABA:Aniline (1:1) Dark 88 0.13% >2% 58 <10.sup.-5 brown CpA413 4ABA:Aniline (1:3) Dark 90 0.25% >2% 55 0.0003 green CpA331 3ABA:Aniline (3:1) Dark 83 0.125 >2 58 <10.sup.-5 brown CpA311 3ABA:Aniline (1:1) Dark 87 0.125 >2 61 <10.sup.-5 brown CpA313 3ABA:Aniline (1:3) Dark 85 0.25 >2 55 0.00005 green CpA231 2ABA:Aniline (3:1) Dark 72 0.125 1 53 <10.sup.-5 brown CpA211 2ABA:Aniline (1:1) Dark 91 0.125 2 52 <10.sup.-5 brown CpA213 2ABA:Aniline (1:3) Dark 93 0.25 >2 56 <10.sup.-5 green

Claims

1. A polyaniline homopolymer or copolymer prepared by the method comprising: preparing an acidic or near neutral (pH 7-8) solution of 15% by weight or higher of a first polyaniline precursor having at least one aromatic amine group and at least one carboxylic acid group in a solvent selected from the group consisting of aqueous methanesulfonic acid and aqueous ammonia; wherein said solution optionally includes one or more additional polyaniline precursors; oxidatively polymerizing said solution and additional polyaniline precursors if present; finally collecting precipitated polyaniline by filtration.

2. A polyaniline homopolymer as in claim 1 wherein the polyaniline precursor is selected from 2-aminobenzoic acid, 3-aminobenzoic acid, or 4-aminobenozic acid.

3. A polyaniline random copolymer as in claim 1 wherein the first polyaniline precursor is selected from either 2-aminobenzoic acid, 3-aminobenzoic acid, or 4-aminobenzoic acid and the second polyaniline precursor is aniline.

4. A polyaniline random copolymer as in claim 3 composed of 3ABA and aniline monomers.

5. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 3ABA and aniline monomers is 1:1.

6. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 3ABA acid to aniline is from 3:1 to 1:3.

7. A polyaniline random copolymer as in claim 3 composed of 2ABA and aniline monomers

8. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 2ABA acid to aniline is 1:1.

9. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 2ABA and aniline monomers is from 3:1 to 1:3

10. A polyaniline random copolymer as in claim 3 composed of 4ABA and aniline monomers

11. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 4ABA acid to aniline is 1:1.

12. A polyaniline random copolymer as in claim 3 wherein the monomer ratio of 4ABA and aniline monomers is from 3:1 to 1:3.