Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-03-24
2003-04-22
Medley, Margaret (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C252S500000, C252S518100, C252S519540, C252S520210
Reexamination Certificate
active
06552107
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a melt or solution processable polyaniline and processes for the preparation of said melt or solution processable polyaniline by using novel dopants synthesised from inexpensive, naturally occurring bimonomers from cashew nut shell liquid. The present invention also relates to a novel process for the preparation of dopants for use in the present invention. The novel dopants employed in the process of the present invention are sulphonic acid derivatives of hydrogenated cardanol (3-pentadecyl phenol), methyl ether of 3-pentadecyl phenol (3-pentadecyl anisol) and phenoxy acetic acid of 3-pentadecyl phenol of the formulae 1, 2 and 3 shown below:
The doping of polyaniline with the dopants described above imparts conductivity to polyaniline and polyaniline doped with these dopants can be used in applications to develop transparent highly conductive films and coatings. Polyaniline which is brittle and unprocessable could be processed by melt or solution techniques by protonating with these functionalized dopants. These conductive polymers show a tremendous promise for industrial applications ranging from electrostatic dissipation to electrochromic displays such as the use in antistatic ESD coatings, absorption of radar frequencies, corrosion prevention, EMI/RFI shielding, electrochemical actuators, lithographic resists, lightning protection, microelectronics, polymer electrolytes, photovoltaics, rechargeable batteries, smart windows, solar cells, bio-sensors etc. One of the significant features of the structure of the dopant prepared by the process of the present invention is that it has a flexible n-alkyl (C
15
H
31
) substituent in the meta position of the aromatic ring which makes the doped polyaniline melt processable and render high solubility for polyaniline in common solvents. The presence of hydrophobic and hydrophilic moieties in the same molecule imparts the polyaniline dopant combination compatibility with a large spectrum of polymers for probing applications involving polymer blends. This enhanced solubility of doped polyaniline makes it possible for the preparation of highly transparent and conductive films and coatings by solution casting or melt processing techniques and conductive plastics could be prepared by blending the doped polyaniline with classical thermoplastic polymers. Thus, these conductive polymers show vast promise for industrial applications such as in static films for transparent packaging of electronic components, electromagnetic shielding, rechargeable batteries, light emitting diodes, non-linear optical devices, sensors for medicine and pharmaceutics and membranes for separation of gas mixtures. The industries to which this invention can be applied are electronic industries, plastics industries, medical industries etc.
BACKGROUND OF THE INVENTION
Polyaniline is one of the most promising conductive polymers due to its uncomplicated polymerisation and excellent chemical stability combined with relatively high levels of conductivity (J. C. Chiang and A. G. Mac Diarmid, synth. Met., 13, 193 (1986). However, it is highly intractable and infusible because of its aromatic nature, the interchain hydrogen bondings and the charge delocalization effects. Emeraldine base form of polyaniline is soluble only in N-methyl-pyrrolidone, selected amines, concentrated sulfuric acid and other strong acids [M. Angelopoulos, A. Ray, A. G. Mac Diarmid and A. J. Epstein, Synth. Met., 21, 21 (1987); X. Tan, Y. Sun, Y. Wei, Makromol. Chem. Rapid Commun. 9, 829 (1988); M. Angelopoulos, G. E. Asturias, S. P. Ermer, A. Ray, E. M. Sherr, A. G. Mac Diarmid, M. A. Akhtar, Z. Kiss and A. J. Epstein, Mol. Cryst Liq. Cryst 160, 151 (1988); A. Andreatta, Y. Cao, J. C. Chiang, A. J. Heeger, P. Smith, Synth. Met. 26, 383 (1988)]. Emeraldine salt is even more intractable. Covalent substitution such as N-alkylation improves melt processability and solubility in various solvents (W. Y. Zheng, K. Levon, J. Laakso, J. E. Osterholm Macromolecules, 27, 7754 (1994). Recently, it was reported that by using functionalised dopants the melt and solution processability of polyaniline can be increased (Y. Cao, P. Smith and A. J. Heeger, Synth. Met., 48, 91 (1992), Y. Cao, P. Smith and A. J. Heeger, PCT Patent Application WO 22/22911, 1992, Y. Cao, P. Smith, Polymer, 34, 3139 (1993), T. Karna, J. Laakso, E. Savolainen, K. Levon European Patent Application EP 0 545 729 A1, (1993) K. Levon, K. H. Ho, W. Y. Zheng, J. Laakso, T. Karna, T. Taka, J. E. Osterholm, Polymer, 36,2733(1995)., C. Y. Yang, Y. Cao, P. Smith and A. J. Heeger synth. Met. 53,293(1993). A. Pron, J. Laakso, J. E. Osterholm and P. Smith Polymer34, 4235(1993), J. Laakso, A. Pron and S. Lefrant J. Polym. Sci. Part A: Polym. Chem. 33, 1437(1995).
Specific functionalised dopants render high solubility for polyaniline into common solvents and can be solution processed from these solvents by solution casting method. Here, the counterions of the dopant simultaneously act as surfactants for bulk polymers or organic solvents. Well known examples of such counterions are p-dodecylbenzenesulfonic acid and camphor sulphonic acid. The solubilizing group can be introduced to the polymer as an inherent part of the dopant while its acidic center protonates it. According to Heeger et al., the m-cresol solution of polyaniline-camphor sulphonic acid allow preparation of films having d.c conductivities up to 400 S/cm. However, m-cresol is suspected to be a cancer causing substance, thus rendering this route instantly undesirable for obtaining soluble, doped PANI (polyaniline) on a large scale.
The main disadvantage of conductive polyaniline is its limited thermal processability. However, from the industrial point of view, the fabrication of a thermally processable conducting polymer would be preferable because it should exhibit appropriate rheological parameters in the temperature range typically used for classical polymer processing (140-220° C.) and it should be thermally processable. No meaningful conductivity decrease should be observed at the processing temperature. Also, the doping should be carried out in situ during processing. Polymers are usually thermally processed in their molten state or plasticized state. The fabrication of a conducting polymer, which would melt in its doped state, is of course, extremely difficult. Many of alkyl or aryl diesters of phosphoric acid induce simultaneous plastification leading to thermal processability of polyaniline.
OBJECTS OF THE INVENTION
The main object of the present invention is, therefore, to provide a process of preparation of melt/solution processable polyaniline by using sulphonic acid dopants synthesized from 3-pentadecyl phenol, which is hydrogenated cardanol.
Another object of the invention is to provide a process for the synthesis of protonated polyaniline by using these dopants and to obtain highly conducting freestanding flexible films and coatings of polyaniline with thermoplastic polymers.
SUMMARY OF THE INVENTION
The sulphonic acid derivatives of 3-pentadecyl phenol which is otherwise known as hydrogenated cardanol, having a long aliphatic hydrocarbon side chain (C
15
H
31
) in the meta position of the aromatic ring, have not been reported to be used as protonating-plasticizing dopants. The introduction of the dopant having the hydrophobic group not only enhances the conductivity of polyaniline but also causes its solubilization and plastification. The doped polymer can, therefore, be thermally or solution processed. There is no report that a sulphonic acid system renders the polyaniline thermally processable. Free standing flexible films could be prepared by the hot pressing method and it exhibits a maximum conductivity value of 40 S/cm. Cardanol is a distillation product of an inexpensive natural material known as cashew nut shell liquid. Cardanol with its long flexible aliphatic side chain has special structural features for chemical modification into functionalised dopants to obtain plasticized polyaniline.
The main finding u
Paul Raji Kannaparampil
Pillai Chennakkattu Krishna Sadasivan
Council of Scientific and Industrial Research
Darby & Darby
Medley Margaret
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