| Summary: | 博士 === 中原大學 === 化學研究所 === 92 === In this study, four derivatives of pyrrole (Py), N-(2-hydroxyethyl) pyrrole (HE), N-(3-hydroxypropyl) pyrrole (HP), N-(2-carboxyethyl) pyrrole (CE) and N-(5-carboxypentyl) pyrrole (CP), were synthesized. Their homopolymers, PHE, PHP, PCE and PCP, and the corresponding copolymers with Py, PYHE, PYHP, PYCE and PYCP, were prepared by galvanostatic electropolymerization and characterized by 1H-NMR, FTIR and EA measurements.
The result of potential-time profiles indicated that a higher potential was required for derivative monomers than Py for the polymerization. This was ascribed to the steric hindrance of high concentration of the N-substituent groups. However, a similar profile was observed for the copolymerization of Py/derivative systems as that of Py due to the reduction of the steric effect by lower content of the substituent. The TGA thermograms showed that all the polymers were thermally stable up to 130 oC and the decomposition temperature of the copolymers occured between those of PPy and the corresponding homopolymers. All the homopolymers showed glass transition temperature (Tg) in DSC thermograms and the presence of long alkyl side chain makes lower Tg that indicates having larger free volume between polymer chain. The identification of Tg of copolymers was difficult, it may be due to their random structures. There are few polymers that polymerized under two-dimensional growth mechanism and showed smoothly morphologies in SEM micrographs. The other polymers polymerized under three-dimensional growth mechanism and showed globular roughly morphologies. This indicates that growth mechanisms would also be affected with different types of functional groups.
Though the derivative polymers have lower conductivity than PPy, but they have better corrosion properties than PPy, especially homopolymers.
The cyclic voltammograms of all polymers are quasi-reversible type electrochemical behavior; moreover, PPy and copolymers showed good cycling stability. The cyclic voltammograms indicated that all the copolymers were larger, while the homopolymers had smaller anodic/cathodic currents and specific charge storages than PPy. This implied that the existence of the proper amount of the N-substituted pendant groups enhanced the ionic mobility in the PPy-based polymers. In addition, the order of redox current of homopolymers are carboxy > PPy > hydroxy that represents hydroxy group having stronger interaction with ions than others. The response of charge/discharge measurements showed the copolymers, which prepared with 80 % Py monomer, having the highest average capacities in each system, even higher than PPy. The copolymers which content higher Py units in each systems show higher capacities than PPy at the 20th cycle and the highest capacity was obtained in CP system. As discussed above, functionalized N-substituted pendent groups can improve the ionic mobility in polymer films that enhancing redox current, specific charge storage and charge/discharge capacity.
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