THE EFFECT OF PYRIDINE RING FUNCTIONALIZATION ON THE CONDUCTIVITY OF CROSS-LINKED CO-POLY(STYRENE-4-VINYLPYRIDINE) DERIVATIVES

The effect of pyridine ring functionalization in crosslinked co-poly(s tyrene-4-vinylpyridine) on electrochemical behavior was studied using impedance spectroscopy. The introduction of a substituent on the nitro gen atom increases conductivity from 10(-14) to around 10(-11) Scm(-1) at room temperature, but the effect of the substituent becomes more e vident at 64 degrees C, at which the n-butyl derivative (co-poly[styre ne-[4-vinyl(N-butylpyridinium bromide)]])-(3) has a higher conductivit y (sigma = 7 X 10(-10) Scm(-1)) than the hydrogen analog (co-poly[styr ene-[4-vinyl(pyridinium bromide)]])-(2) (sigma = 4.3 X 10(-10) Scm(-1) ), while the iodo derivative (co-poly[styrene-[4-vinyl(N-iodopyridiniu m bromide)]])-(6) has a conductivity ten times lower. Further increase in the conductivity was observed upon the substitution of the bromine anion with the three-bromide anion (Br-3)(-), but the effect depends on the substituent on the nitrogen atom: 4.4 times higher conductivity was found for the hydrogen pyridinium salt (4) in comparison with sam ple (2), and the conductivity increases SO-fold for the N-butyl deriva tive (5) compared with sample (3). The conductivity increased exponent ially with temperature and the activation energy values vary from 0.76 to 1.01 eV. Impedance responses for dried samples of pyridinium salts (2), (3), (4), (5), and (6) suggested electron-type conductivity. The conductivity of crosslinked polymers depends very much on the conditi ons, and increases by several orders of magnitude when water or methan ol is present in the atmosphere during measurement. The conductivity a lso depends on the structure of the substituent attached to the nitrog en atom: sigma = 5 X 10(-4) Scm(-1) and sigma = 2 X 10(-4) Scm(-1) for hydrogen bromide (2) and N-butyl bromide derivative (3), but the cond uctivity of the N-iodo derivative (6) changed very little. In contrast , the impedance responses for samples stored in the presence of water or methanol suggested ion conductivity. (C) 1996 John Wiley & Sons, In c.