|Title of Invention||
AN IMPROVED PROCESS FOR THE PREPARATION OF POLYANILINE-SULFATE
|Abstract||The present invention provides process for the preparation of polyaniline-sulfate without using any protonic acids. The present invention more particularly provides an emulsion-polymerization process for preparing an electrically conductive polyaniline-sulfate wherein the polyaniline-sulfate is in organic carrier solvent.|
|Full Text||The present invention relates to a process for the preparation of polyaniline-sulfate. The present invention particularly relates to a process for the preparation of polyaniline-sulfate without using any protonic acids. The present invention more particularly relates to an emulsion-polymerization process for preparing an electrically conductive polyaniline-sulfate wherein the polyaniline-sulfate is in organic carrier solvent.
Electrically conducting polymers are subjected to in-depth research worldwide These polymers offer the possibility of replacing metallic conductors and semiconductive materials in a variety of applications including batteries, transducers, switches, photocells, circuit boards, heating elements, antistatic protection (ESD) and electromagnetic protection (EMI). Conducting polymers possess the following advantages over metals: light weight, advantageous mechanical properties, good corrosion resistance and lower cost of synthesis and fabrication.
The benefits of intrinsically conducting plastics include easy modification of their conductivity as a Sanction of doping conditions, which is particularly accentuated in conjunction with low conductivities. Exemplifying kinds of intrinsically conducting polymers are polyacetylene, poly-p-phenylene, polypyrrole, polythiophene and polyaniline.
The use of most intrinsically conducting plastics in the promising applications mentioned above is, however, limited by the inferior processability and stability properties of those polymers.
A technically and commercially promising intrinsically conducting polymer is polyaniline and its derivatives. An aniline polymer is based on an aniline unit in which the nitrogen atom is bonded to the para-carbon in the benzene ring of the next unit. Unsubstituted polyaniline can occur in several different forms such as leucoemeraldine, protoemeraldine, emeraldine, nigraniline and toluprotoemeraldine.
Polyaniline is recognized as being chemically stable and electrically conductive in the protonated form. Nevertheless, the use of polyaniline has been limited because it has been considered intractable or unprocessible.
Aniline can be polymerized to polyaniHne either by chemical or electrochemical route. The synthesis of polymer by either chemical or electrochemical methods depends upon the intended application of the polymer. Wherever thin films are required an electrochemical method is preferred. In the preparation of polyaniline solution, chemical method is preferred.
Synthesis of polyaniline is commonly performed by the method of chemical oxidative polymerization based upon an aqueous solution polymerization system, (see Cao et al.. Polymer, 30:2305, 1989). This method involves combining water, a protonic acid, aniline and an oxidizing agent and allowing the mixture to react while maintaining the reaction mixture at constant temperature. After a period of several hours, the precipitated polyaniline is separated from the reaction mixture and washed. The material synthesized by this approach is insoluble in organic solvents and predominantly amorphous. (Annis et al.. Synthetic Metals 22:191 et seq., 1986)
The production of the polyaniline salt by doping the polyaniline to the protonated, conducting form with acids as well as the synthesis of conducting polyaniline salts of protonic acids, (see, for example, Tzou and Gregory, Synthetic Metals 53:365-77, 1993; Cao et al.. Synthetic Metals 48:91-97, 1992; Osterholm et al.. Synthetic Metals 55:1034-9, 1993 which are incorporated by reference). The protonic acid serves as a primary dopant providing the counter ion for the protonated emeraldine base form of the polyaniline.
Cao et al. reported a method to prepare polyaniline salts of a number of protonic acids including 4-dodecylbenzene sulfonic acid and dinonylnaphthalene sulfonic acid. (Cao et al., Synthetic Metals 48:91-97, 1993; Cao et al., U.S. Pat. No. 5,232,631, 1993). The polyaniline salts were reported to be soluble in nonpolar solvents such as xylene; however, the solubility appeared to be very low. For example the maximal solubility of the dodecylbenzenesulfonic acid salt of polyaniline was less than 0.5%.
Polyaniline base (emeraldine base) can be dissolved in N-methy-pyrrolidone, concentrated sulfuric acid and other strong acids (Cao et al.. Synthetic Metals 26, 283 (1988), which are diflficuh to apply commercially on account of their prohibitive cost or strong corrosion.
One of the methods of processing of polyaniline consisting of doping the polyaniline to the conducting form with acids and dissolving in organic solvents. Tzou and Gregory (Synthetic Metals 53:365f-377, 1993) used the approach and reported that polyaniline salts containing carboxyl and amino substituents were soluble in the polar solvents, N-methyl-2-pyrrolidinone and dimethylsulfoxide. In contrast, in the same solvents the polyaniline salts of dodecylbenzenesulfonic acid, 1,5-naphthalenedisulfonic acid and p-toluenesulfonic acid were insoluble or were unstable and precipitated
To improve the processability, emulsion polymerization processes for preparing a polyaniline salt of a protonic acid have been reported. (Cao et al., U.S. Pat. No. 5,232,631, Example 6B, 1993; Cao and Jan-Erik, WO94/03528, 1994 I; Cao and Jan-Erik, U.S. Pat. No. 5,324,453, 1994 II; see also, Osterholm et al., P. Synthetic Metals 55:1034-9, 1993). In these disclosures aniline, a protonic acid, and an oxidant were combined with a mixture of polar liquid, typically water and a non-polar or weakly polar liquid, e.g. xylene, chloroform, toluene, decahydronaphthalene and 1,2,4-trichlorobenzene, all of which are either sparingly soluble or insoluble in water.
Smith et al (Polymer 35, 2902, (1994)) reported the polymerization of aniline in an emulsion of water and a non polar or weakly polar organic solvent. This polymerization was carried out in the presence of functionalized protonic acid such as dodecylbenzenesulfonic acid which simultaneously acted as a surfactant and protonating agent for the resulting polyaniline. This polyaniline is partially soluble in non polar solvents.
Protonic acid primary dopants are described as acting as surfactants in that they are purportedly compatible with organic solvents and enable intimate mixing of the polyaniline in bulk polymers (Cao et al, Synthetic Metals 48:91-97, 1992; Cao et al, U.S. Pat. No. 5,232,631, 1993 which are incorporated by reference). Thus, any surfactant aspect of the primary dopants was thought to contribute to the processability rather than the conductivity of the polyaniline.
Heeger's group (Synthetic Metals 48, 91 !992); Synthetic Metals 3514 (1993) reported that emeraldine base doped with a functionalized protonic acid, for example, camphorsulfonic acid and dodecylbenzene sulfonic acid, can be dissolved in a non-polar or moderate polar organic solvent. This three component system has good solubility in common organic solvents and is compatible with many of the classical polymers. References may be made to other citations such as
"Polyaniline : Conformational Changes Induced in Solution by Variation of Solvent and Doping Level" by Jamshid K. Avlyanov, et al., Synthetic Metals, vol. No. 72 (1995) pp. 65-71; "Secondary Doping in Polyaniline" by Alan G. MacDiarmid and Arthur J. Epstein, Synthetic Metals, vol. No. 69, (1995), pp. 85-92; "Morphology of Conductive, Solution-Processed Blends of Polyaniline and Poly(Methyl Methacrylate)" by C.Y. Yang, et al.. Synthetic Metals, vol. No. 53, (1993), pp. 293-301; and "Counter-Ion Induced Processability of Conducting Polyaniline and of Conducting Polyblends of Polyaniline in Bulk Polymers" by Yong Cao, Paul Smith and Alan J. Heeger, Synthetic Metals, vol. No. 48 (1992), pp. 91-97.
Polyaniline salt has been categorized as a interactable material which is neither soluble nor fusible under normal conditions. Several strategies were worked out to introduce solubility and processability in polyaniline. They are :
" Preparation of substituted polyaniline, preparation of polyaniline copolymers which are
not the homopolymer of polyaniline salts. ® Dissolving the polyaniline salt in concentrated acid. However, they are highly corrosive
because the use of concentrated acid. 9 Preparation of polyaniline salt using functionalized protonic acids both by aqueous and
emulsion polymerization process, which are costly process. The present method involve a process for the polymerization of aniline in to polyaniline-sulfate salt without using any protonic acids, wherein the polyaniline-sulfate in carrier organic solvent.
The main object of the present invention is to provide a process for the preparation of polyaniline-sulfate.
The other object of the present invention is to provide a process for the preparation of polyaniline-sulfate without using any protonic acids.
Another object of the present invention is to provide a process wherein, the electrically conductive polyaniline-sulfate is in weakly polar solvent.
Yet another object of the present invention is to provide a process for the preparation of an electrically conductive polyaniline-sulfate in the powder form.
Accordingly the present invention provides an improved process for the preparation of polyaniline-sulfate which comprises polymerizing a aromatic amine selected from aniline or substitute aniline in the presence of mixture of water and hydrocarbon solvents such as herein described, optionally in the presence of anionic surfactant and radical initiator at temperature in the range of 25° - 30°C for the least 4 hrs., separating the polyaniline-sulfate from the reaction mixture by conventional filtration method.
The present invention is directed to a process for the preparation of an electrically conductive polyaniline-sulfate in non aqueous organic carrier solvent.
The present invention is also directed to a process for the preparation of an electrically conductive polyaniline-sulfate in the powder form.
In an embodiment of the present invention, the aromatic amine used may be aniline or substituted aniline.
In an another embodiment of the present invention hydrocarbon solvent used may be chlorinated solvent such as chlorofomn, dichloromethane, aromatic hydrocarbon such as xylene.
In yet another embodiment of the present invention, the anionic surfactant used may be such as sodium lauryl sulfate, sodium octyl sulfate, sodium docyl benzene sulphonate.
In still yet another embodiment of the present invention, the radical initiator used may be ammonium persulfate, sodium persulfate.
In feature of the present invention, the separation of polyaniline sulfate in organic solvent may be effected by pouring the reaction mixture in to water in case of surfactant has been used in the reaction mixture.
In another feature of the invention, the separation of the polyaniline-sulfate salt from the reaction mixture may be carried out by filtration when the surfactant is not used in the reaction.
These embodiments will be apparent from the ensuing detailed description of the present invention.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention
The following example illustrates the preparation of the polyaniline-sulfate in weakly polar organic solution by the emulsion-polymerization pathway.
A solution containing 1.44 g of sodium lauryl sulfate dissolved in 40 ml of distilled water is mixed with 2.3 ml aniline in 60 ml chloroform. The milky-white emulsion thus formed is mechanically stirred at 25°C. Ammonium persulfate (5.71 g) in 100 ml of water, is added dropwise to the mixture over a period of approximately 20 minutes. The reaction is allowed to proceed for 4 hours. The color of the emulsion at this time becomes green. The contents of the reactor, are transferred to a beaker which contains 1500ml water, at which time the emulsion separated into bottom oily green phase containing the polyaniline and a upper aqueous phase. The upper aqueous phase is removed with a separating furmel and 1500 ml water is added to the green phase, the aqueous phase is removed and the green polyaniline phase is subsequently washed with three 1500 ml portions of water. Sodium sulfate (5 g) is added to the polyaniline phase and filtered through fiher paper. The polyaniline phase thus obtained is appeared uniform to the naked eye and the polymer remained solubilized in the organic phase.
Using the same process, polyaniline-sulfate are also prepared by varying the amounts of surfactant.
The isolated polyaniline-sulfate samples are analyzed by electronic absorption spectral technique using Hitachi U 2000 spectro photo meter. Polyaniline-sulfate salt in organic solvent according to Examples 1 are recorded and three peaks are observed at around 380, 535 and 860 nm which corresponds to polyaniline-salt system.
The following example illustrates the preparation of the polyaniline-sulfate in the powder form by the emulsion-polymerization pathway.
The organic layer obtained in Example 1 which contains polyaniline-sulfate salt in organic solvent is poured into 500 ml of acetone. Polyaniline-sulfate salt is thus precipitated out from the organic solvent. The precipitate is then recovered by filtration and the solid is washed with 2000 ml of distilled water followed by 250 ml of acetone. The powder is dried at 100°C, till the constant mass is reached.
The polyaniline-sulfate salts in the dry powder form are compressed into pellets using a 16 mm diameter Macro-Micro KBR die and a 12-ton laboratory hydraulic press. The powder is placed in the die and a pressure of 2000 lbs is applied. Each pellet thus formed is measured to determine its diameter and thickness. The pellets are in the shape of disks. In measuring the conductivity a pellet is coated with silver paint on both the sides having the same cross sectional area and the resistance is measured using an ohmmeter. Lead resistance is 0.03 Ohms for the pellets. Conductivity is calculated using the following formula:
Conductivity = (Thickness)/(resistance.times.area) = d/(RA)
The conductivity of the polyaniline-sulfate prepared by Example 2 using 0.16, 0.36, 0.72, 1.08 w/v of surfactant are found to be 3.4 x 10-4, 3.7 x 10-4 3.0 x 10-3 and 4.2 x 10-3 S/cm respectively.
Thermal analyses are performed by the simultaneous differential thermal analysis and thermogravimetric analysis technique using the Metier Toledo Star system and accordingly the samples of Example 2 are evaluated. Polyaniline-sulfate samples are found to be stable up to 200.degree. C.
The following example illustrates the preparation of the polyaniline-sulfate salt without using any surfactants and protonic acids.
Aniline (2.3 ml) is dissolved in 100 ml of distilled water. Ammonium persulfate (5.71 g) in 100 ml of water, is added dropvase to the mixture over a period of approximately 20 minutes at 25'C. The reaction is allowed to proceed overnight for 4 hours. The precipitate thus obtained is separated from the reaction mixture and washed with 3000 ml water followed by 300 ml of acetone. . The powder is dried at 100°C, till the constant mass is reached.
The conductivity of the polyaniline-sulfate prepared by aqueous polymerization method i.e., without using any surfactants and protonic acids is found to be 4.2 x lO-5S/cm. The above results indicate that
9 Ammonium persulfate is acting as oxidizing agent as well as protonating agent.
9 The efficiency of oxidation and protonation of aniline into polyaniline-sulfate salt by
ammonium persulfate is increased by the use of surfactant. 9 Emulsion polymerization pathway provides polyaniline-sulfate in solvent, however, aqueous polymerization yield polyaniline-sulfate in the powder form.
The main advantages of the present invention are : (i) the preparation of polyaniline-sulfate without using any protonic acids and especially functionalized protonic acids, and (2) the preparation of an electrically-conductive polyaniline-sulfate which is in organic solvent.
In view of the above, it will be seen that several advantages of the invention are achieved and other advantageous results attained. As various changes could be made in the above methods and compositions without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
1. An improved process for the preparation of polyaniline-sulfate which comprises polymerizing a aromatic amine selected from aniline or substitute aniline in the presence of mixture of water and hydrocarbon solvents such as herein described, optionally in the presence of anionic surfactant and radical initiator at temperature in the range of 25° - 30°C for the least 4 hrs., separating the polyaniline-sulfate from the reaction mixture by conventional filtration method.
2. A process as claimed in claims 1 - 2, wherein the polyaniline-sulfate is in the powder form and is electrically conductive.
3. A process as claimed in claims 1-3 , wherein the hydrocarbon solvent used is selected from chloroform, dichloromethane xylene.
4. A process as claimed in claims 1-3, wherein the anionic surfactant used is selected from sodium lauryl sulfate, sodium octyl sulphate, sodium docyl benzene sulphonate.
5. A process as claimed in claims 1-4, wherein the radical initiator used is ammonium persulfate or sodium persulfate.
6. A process for the preparation of polyaniline-sulfate salt by emulsion polymerization pathway substantially as herein described with reference to the examples.
|Indian Patent Application Number||295/DEL/2000|
|PG Journal Number||38/2010|
|Date of Filing||23-Mar-2000|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG NEW DELHI-110001, INDIA.|
|PCT International Classification Number||H01B 001/12|
|PCT International Application Number||N/A|
|PCT International Filing date|