Conducting graft copolymers of pyrrole and thiophene with random copolymers of methyl methacrylate and 3-methylthienyl methacrylate
Introduction
Conducting polymers (CPs) are an exciting new class of electronic materials, which have attracted rapidly increasing interest since Shirakawa's report in 1977 [1]. CPs are beginning to find applications in the fields of battery materials [2], electrochromic devices [3], [4], electromagnetic shielding [5], sensor technology [6], non-linear optics [7], molecular electronics [8] and enzyme immobilization matrices [9], [10] since they have combined properties of metals and polymers. Many unsubstituted conducting polymer systems have limited solubility and are intractable and infusible. This is due to the rigid rod nature of CPs, arising from their extended-delocalization. In order to make the polymer soluble, fusible and processable, polythiophene substitution at three and/or four position was achieved by various groups [11], [12]. Synthesis of conducting polymer composites, graft and block copolymers were shown to be effective ways to compensate for the certain deficiencies of conducting polymers like poor mechanical and physical properties. Electropolymerization of the conducting component on an electrode previously coated with the insulating polymer is one of the most widely used method for that purpose [13], [14], [15].
Recently, conducting copolymers of thiophene functionalized methyl methacrylate with thiophene and/or pyrrole have been utilized [16], [17]. In this work, syntheses of random copolymers (RC) of 3-methylthienyl methacrylate (MTM) and methyl methacrylate (MMA) were achieved by free-radical polymerization with the use of azobisisobutyronitrile (AIBN) as the initiator. Conducting graft copolymerization of random copolymers with thiophene and/or pyrrole was achieved by constant potential electrolysis. The grafting process was elucidated with conductivity measurements, cyclic voltammetry, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetry analysis, scanning electron microscopy studies.
Section snippets
Materials
The monomers, pyrrole (Py) (Aldrich), thiophene (Th) (Sigma), methyl methacrylate (MMA) (Aldrich), dimethyl formamide (Aldrich) and methacryloyl chloride (Aldrich) were purified by conventional distillation procedures prior to use. 2,2-Azobisisobutyronitrile (AIBN) (Aldrich) was recrystallized from ethanol. The electrolysis solvents, acetonitrile (AN) (Merck), and dichloromethane (Merck) were used without further purification. The supporting electrolytes, p-toluene sulfonic acid (PTSA) (Sigma)
Synthesis of random copolymers 3-methylthienyl methacrylate and methyl methacrylate
MTM and MMA of random copolymers of three different compositions were polymerized by free radical bulk polymerization in the presence of AIBN as the initiator (Scheme 1).The results of the polymerization are presented in Table 1 (RC1, RC2, and RC3).
Cyclic voltammetry
CV experiments were carried out in an ACN–TBAFB system under N2 atmosphere by a Bank Pos2 potentiostat/galvanostat. Fig. 1 depicts the redox behavior of pyrrole, thiophene, and RC1 in the presence of thiophene and pyrrole. In the cyclic voltammogram
Conclusions
Random copolymers of methyl methacrylate and 3-methylthienyl methacrylate were successfully synthesized by free radical polymerization with AIBN as the initiator. Graft copolymers of RC with polypyrrole were further synthesized by two different electrochemical methods. Constant potential electrolyses (CPE) were carried out in ACN–TBAFB and water–PTSA solvent–electrolyte couples, with 1.1 V at room temperature. Graft copolymers of RC were also synthesized with polythiophene in the presence of
Acknowledgements
This work was supported by DPT2003K120920-02, METU BAP-2003-01-03-02, Istanbul Technical University Research Fund and Turkish Academy of Sciences (TUBA).
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