Semiconduction in phenylene polymers

Abstract

The semiconductive behaviour of compressed discs of polymers in the polyphenylene series has been examined. Some polymers showed a resistance increase with time to an equilibrium value, possibly due to space charge effects, but after allowance for this the conductivity was ohmic up to 500 V/cm or beyond. Thermoelectric power results pointed to electronic rather than ionic conduction, with positive holes as majority carriers, and in one case (polybenzone) a mobility of 3·8 × 10 −4 cm 2/V sec was established, in agreement with expectations from band theory for an intrinsic semiconductor. The polyaromatics gave relatively high energy-gap values which agree with values found for the monomers which have been associated with electron injection. This applies in the absence of bridging groups, and also for the bridging groups CH 2 and O. Certain other bridging groups, in order of increasing effectiveness AsO(OH), AsPh, CO and NH gave polymers with energy-gaps lower than the monomer values. Presumably these groups allow the extension of conjugation between the monomers along the polymer chain, and result in intrinsic semiconduction. Hydrogen, oxygen and nitrogen have no effect, but boron trifluoride gas increases the conductivity of the polymers, supporting the positive hole concept.