Temperature-conductivity characteristics of the composites consisting of fractionated poly(3-hexylthiophene) and conducting particles

Poly (3-hexylthiophene) (P3HT) synthesized by oxidative polymerization was fractionated by molecular weight by using organic solvents. The fraction of higher average molecular weight gave higher regioregularity and conductivi ty. Composites of the P3HT fraction having the highest molecular weight wer e prepared by use of the following conducting particles as fillers: titaniu m carbide (TiC), indium tin oxide (ITO), and carbon black (CB). Temperature -conductivity profiles of the composites showed that the resistance change with PTC (positive temperature coefficient) effect was strongly influenced by the content and size of conducting particles and the molecular weight of P3HT. Although no significant PTC effect for P3HT-CB composite and little effect for P3HT-ITO composite system were observed, the P3HT-TiC composite containing TIC of 70-80 wt % showed an obvious PTC effect that brought the conductivity change by about four orders of magnitude near the glass transi tion temperature of P3HT. However, such a remarkable PTC effect was not obs erved for the P3HT-TiC composite prepared with the P3HT fraction of low-mol ecular weight. It was shown that a good PTC effect could be achieved by the composite consisting of the P3HT of high-molecular weight and the conducti ng particles of relatively large size. (C) 2000 John Wiley & Sons, Inc.