ISS: 0973-4945; CODE ECJHAO E- Chemistry http://www.ejchem.net 2012, 9(4), 2332-2337 Synthesis and Characterization of Boron Trifluoride Doped High Performance Polyaniline K. BASAVAIAH 1*, D. SAMSOU 2, AD A. V. PRASADA RAO 1 1 Department of Inorganic and Analytical Chemistry, Andhra University, Visakhapatnam- 530003, India 2 Departments of Organic, Foods, Drugs and Water, Andhra University, Visakhapatnam- 530003, India klbasu@gmail.com Received 28 July 2011; Accepted 4 October 2011 Abstract: We report simple synthesis of boron trifluoride (BF 3 ) doped defect free high performance polyaniline (HPPAI) in two step method. Firstly, HPPAI was prepared via self-stabilization dispersion polymerization method in a heterogeneous reaction medium. Second step involves doping of emeraldine base form of HPPAI with boron trifluoride under reduced vacuum. The resultants BF 3 doped HPPAI have been well characterized by using UV- Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetry. The spectroscopic data indicated that the interaction between HPPAI and BF 3.Thermogravimetry studies revealed that the BF 3 doping improved the thermal stability of defects free PAI. Keywords: Conducting polymers; High performance PAI; Doping; Boron trifluoride; Thermal stability. Introduction Conducting polymers have attracted increasing attention because they offers the possibility of generation of novel materials with diverse applications for electromagnetic interference (EMI) shielding, rechargeable battery, chemical sensor, organic light emitting devices, corrosion devices, and microwave absorption 1 5. Among conducting polymers, polyaniline (PAI) is the promising electrical conducting polymer due to its a broad range of tunable properties derived from its structural flexibility, good environmental stability, easy preparation in aqueous solution, and organic solvents, optical, electrical properties and unique redox chemistry 6-7. Moreover, PAI exhibits a large spin density so interesting electrical and magnetic properties arise that are highly dependent on the doping level and the structure of the polymer. However, PAI suffers from poor processability because it is infusible and insoluble in common solvents.
Synthesis and Characterization of Boron Trifluoride Doped 2333 PAI synthesized in standard Mac Diarmid method 8, the macroscopic precipitation polymerization of aniline occurs at the interface of growing particles and the aqueous reaction medium and also inside the swollen particles. The resulting PAI has defects due to a randomly branched backbone, some cross linking, ortho-coupling, and Michael reductive addition of aniline 9. To prevent the undesired side reaction and macroscopic precipitation, several methods have been developed and the most effective method is self-stabilized dispersion polymerization in a heterogeneous medium. A defect free PAI was prepared by self-stabilized dispersion polymerization method in heterogeneous medium 10. The rationale behind this method is that the organic phase acts to separate the insoluble aniline oligomers and grow PAIchains from the reactive ends of the chains in the aqueous phase. Thus prevent the macroscopic precipitation and undesired side reactions. In this study, we reoprt synthesized defect free PAI via self-stabilized dispersion polymerization method in heterogeneous reaction medium. The emeraldine base form of defect free PAI was doped with boron trifluoride (BF 3 ) by using BF 3 -etharate complex under control atmosphere. Experimental Aniline, Boron trifluoride- Etherate (BF 3 -Etherate), Ammonium persulphate [APS, (H 4 ) 2 S 2 O 8 ], Chloroform, Methanol, Sodium hydroxide (aoh) were obtained from Merck Chemicals, India and used as received. Aniline was double distilled under reduced vacuum and stored at 0-5 o C before use. Double distilled water was used throughout all the synthetic processes. All other reagents were analytical grade and used without further purification. Synthesis of High performance Polyaniline (HPPAI) In typical synthesis, aniline solution in 1M HCl was added to a chloroform / water mixer (1:2 vol./vol.) and stirred at -16 0 C until the solution became colloidal dispersion. A precooled acidic solution of oxidant, ammonium persulfate, (APS) was added drop wise to the colloidal dispersion, with rigorous stirring. The polymerization reaction was preceded for another 12 hours at -16 0 C. The colloidal dispersion slowly tuned to the dark green colour characteristic of PAI. The reaction mixture was filtered, washed with water and methanol periodically to remove unreacted reagents. Finally, dedoped with 0.5 M aoh solution and dried under dynamic vacuum at room temperature. Preparation of Boron Trifluoride (BF 3 ) Doped High Performance Polyaniline EB form of HPPAI powder was doped with boron trifluoride (BF 3 ) using boron trifluorideetharate complex under anhydrous condition because high susceptibility of BF 3 towards hydrolysis, doping was carried out strictly anhydrous conditions. BF 3 -Etherate, 1:1 complex of BF 3 and diethyl ether was used for doping. In order to reduce the exposure to atmosphere, BF 3 -etherate was distilled in vacuum and distillate was collected directly over the emeraldine base HPPAI powder. The reactivity of BF 3 in BF 3 etherate complex is remarkably reduced, makes it a lot easier to handle. In order to achieve maximum doping, excess dopant was added and reaction mixture was left to equilibrate for 24 hours and after which un-reacted BF 3 -etherate was removed under dynamic vacuum at room temperature. Pumping for longer period of time, leads to partial dedoping. Characterization The UV-Visible absorption spectra of the samples were recorded on a Perkin-Elmer double beam LS-50 spectrophotometer. The samples were dissolved in dry dimethylsulphoxide (DMSO) and centrifuged to remove any undissolved polymer. The clear solutions were taken in quartz cuvettes. The infrared spectra were recorded over the range 4000-400 cm -1
2334 K. BASAVAIAH et al. in a Perkin-Elmer Model SPECTRUM 1000 FTIR spectrometer. The powdered samples were mixed thoroughly with KBr and pressed into thin pellets. Morphology of BF 3 doped HPPAI was examined by scanning electron microscopy (SEM). Results and Discussion PAI can be considered as Lewis base due to a lone electron pair on itrogen atoms of PAI. Recently, it was evidenced that the PAI can be doped with Lewis acids and forms acid- base complexes 11. Like other Lewis acids, BF 3 can also form a complex with PAI. The general structure of PAI doped with Lewis acid () is presented in figure1. Similarly to the case of protanation, one molecule of dopant is coordinated to nitrogen atom of PAI, but contrary to the protation, both types of nitrogen atoms of PAI( amine as well as imine ones) are coordinated by. In this case of the formation of a covalent or mixed ionic covalent bond was proposed. The structures of Lewis acid doped PAI is differ significantly from those of protanated PAI. Lewis acid-doped PAI systems are expected to be different from the conventional protonated PAI owing to a qualitatively different chemical interaction between the dopant and the polymer; for instance, the absence of any counter ion in these systems may have different influence on the properties. Thus spectroscopic properties of BF 3 doped PAI systems differ from those of protonated PAI. H H H Figure 1. Chemical structure of Lewis acid (BF 3 ) doped emaraldine base PAI. Molecular structure of BF 3 doped HPPAI was investigated by UV-Visible spectroscopy and Fourier-transform infrared (FTIR) spectroscopy. UV-Visible absorption spectra for both undoped HPPAI and BF 3 doped HPAI shown in Figure 2. Undoped HPAI gives two electronic absorption bands at 330 nm and 630 nm approximately. The broad absorption feature at 630 nm has been assigned to quinoid formation in the backbone of the PAI, while the band at 330 nm is assigned to the π π * electronics transition of benzenoid rings in the HPPAI. In case of BF 3 doped HPAI, new absorption bands appears at 450 nm and 830 nm. These features confirmed the BF 3 doping to HPPAI. It is important to note that the same changes have also been observed in the case of proton doped PAI 12-13.
Absorption Synthesis and Characterization of Boron Trifluoride Doped 2335 Wavelength/nm Figure 2. UV-Visible spectra of (a) undoped HPPAI (b) BF 3 doped HPPAI. Figure 3 shows FTIR spectrum for BF 3 doped high performance polyaniline, which well agreed with the previous literature 14-18. Wavenumber Figure 3. FTIR spctrum for BF 3 doped HPPAI. The FTIR spectrum gives main characteristic peaks at 3180, 1595, 1496, 1408, 1313, and 827 cm -1. Peaks at 3180, 1595, and 1496 cm -1 due to -H stretching vibration, C=C stretching of quinoid phenyl and benzenoid phenyl rings, respectively. The peak at 1408 cm -1 is due to stretching frequency of B-=Q moiety (B refers to benzenoid and Q refers to quinoid ring). The presence of this peak confirms that the HPPAI is doped with BF 3. The peak at 1313 cm -1 is assigned to C- stretching vibrations of the 1, 4- disubstituted benzene ring of HPPAI. The peak at 827 cm -1 corresponds to C-H out of plane bending of 1, 4-disubstituted benzene rings of HPPAI. Figure 4. Scanning electron microscopy (SEM) images of for BF 3 doped HPPAI.
Weight, % Deriv Weight, % o C 2336 K. BASAVAIAH et al. Morphology of BF 3 doped high performance PAI was investigated by scanning electron microscopy. SEM images of BF 3 doped HPPAI is shown in Figure 4. SEM images illustrate the synthesized HPPAI particles morphologies at a variety of dimensional levels. Figure 5 shows a TG DTG curve of BF 3 doped HPAI prepared via self-stabilized dispersion polymerization of aniline under 2 flow at a heating rate of 20 0 C per minute from 50-850 0 C. The first region at lower temperatures (<350 0 C) is due to removal water and other volatiles in BF 3 doped HPPAI. The weight loss in temperature range of 350-550 0 C can be ascribed to the removal of BF 3 and decomposition of HPPAI chain. The third weight loss region of 550-840 0 C is due to decomposition of HPPAI chain. Thermal studies indicated that thermal decomposition of HPPAI chain occurs at higher temperature for BF 3 doped HPAI as compared to PAI synthesized by standard method. Temperature, o C Figure 5. TG-DTG of BF 3 doped HPPAI under 2 atmosphere flow at a heating rate of 20 0 C min -1. Conclusion We have demonstrated a simple, reproducible, and facile method of synthesis of BF 3 doped HPPAI via self-stabilization dispersion oxidative chemical polymerization technique and doping with BF 3 -etherate under controlled atmosphere. The spectroscopic results indicated that successful synthesis of BF 3 doped HPPAI. TG data indicated that the thermal stability of BF 3 doped HPPAI have higher than PAI prepared by conventional method. TG reveals that higher thermal stability is due to the doping HPPAI with BF 3. Acknowledgment This work was supported by the Ministry of Ocean and Environmental Sciences (MOES) (Project Grant o. MOES / 11-MRDF/1/28/P/08), ew Delhi, India.
Synthesis and Characterization of Boron Trifluoride Doped 2337 References 1. Mäkelä T, Pienimaa S, Taka T, Jussila S, and Isotalo H, Synth Met., 1997, 85, 1335. 2. Kuwabata S, Masui S, and Yoneyama H, Electrochim Acta, 1999, 44, 4593. 3. Kan J Q, Pan X H and Chen C, Biosens Bioelectron., 2004, 19, 1635. 4. Ahmad and MacDiarmid A G, Synth Met., 1996, 78, 103. 5. Rose T L, D Antonio S, Jillson M H, Kron A B, Suresh R, and Wang F, Synth Met., 1997, 85, 1439. 6. MacDiarmid A G, Angew Chem Int Ed., 2001, 40, 2581. 7. MacDiarmid A G, Synth Met., 2002, 125, 11. 8. Zhang X, Sadighi J P, Mackewitz T W, and Buchwail S L, J Am Chm Soc., 2000, 122, 7607. 9. Mac Diarmid A G, Chiang J, Richtr A F, Somarisi L D, and Epstin A J, in conducting polymers (Ed., Alcacer L), Reidel, Dordrecht, The etherlands 1987, 105. 10. Rao P S, Sathyanarayana D, and Palaniappan S, Macromolecules, 2002, 16, 5841. 11. Genoud F, Kulszewicz-Bajer I, Bedel A, Oddou J-L, Jeandey C, and Pron A, Chem Mater., 2000, 12, 744. 12. Venugopal G, Quan X, Johnson G E, Houlihan F M, E. Chin E, and O.nalamasu, Ce. Mate., 1995, 7, 271. 13. Hasik M, Kurkowska I, Bernasik A, React Funct Polym., 2006, 66(12), 1703. 14. Zang L, Wan M, Wei Y, Macromol Rapid Commun., 2006, 27, 366. 15. Chen S-A and Lee H T, Macromolecules, 1995, 28, 348. 16. Trhcova M, Stejskal J and Prokes J, Synth Met, 1999, 101, 840. 17. eoh K G, Pun M Y, Kang E T, and Tan K L, Synth Met., 1995,73, 209. 18. Kim B-J, Oh S-G, Han M-G, and Im S-S, Langmuir, 2000, 16, 5841s.
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