Effect of electron donor/acceptor substituents on the Seebeck coefficient and thermoelectric properties of poly(3-methylthiophene methine)s/graphite composites

Recently, the use of polymers as thermoelectric materials has attracted considerable attention. However, relatively few studies have investigated the effects of polymer structures on the corresponding thermoelectric properties of the polymers. In this work, a series of poly(3-methylthiophene methine)s (PMMs) were synthesized for use as thermoelectric materials, and the effects on the Seebeck coefficient of donor or acceptor side groups at the methine carbon were studied. The PMMs with strongly electron-withdrawing and electron-donating groups exhibited the highest Seebeck coefficients. Motivated by the high Seebeck coefficients of the selected PMMs, PMM/graphite composites were prepared via solution mixing followed by mechanical ball milling and cold pressing. The thermoelectric properties of the composites were investigated as a function of the graphite (G) concentration. The highest ZT (6.23 × 10−3) was measured for the poly[(3-methylthiophene-2,5-diyl) (p-(methoxy)benzylidene)]/G composite that contained 90 wt% G. The results of this work suggest that the thermoelectric properties of polymer-inorganic composites can be improved by designing polymers with high Seebeck coefficients.