Aggregation Behavior of Rodlike Ionogenic Polymers in Chloroform

Abstract

The rodlike ionogenic polymers poly(p-pyridylene-phenylene) and poly(p-pyridylene/phenylene-ethynylene) form polyelectrolytes when protonated with toluene sulfonic acid or ethane sulfonic acid in chloroform solution. This molecular modification, clearly indicated by a marked red shift of the UV absorption band, induces the formation of prolate, bundlelike aggregates, whose size and shape are obtained from their rotational dynamics as revealed by electric birefringence relaxation and their translational dynamics as measured by dynamic light scattering. The aggregates have a length of 400-600 nm and a high aspect ratio >15. In general, the polyelectrolyte molecules are arranged with their long axes parallel to the long axis of the aggregates. They probably attract each other through the electrostatic interaction with counterions. The counterions are not bound to specific sites but may be shifted under the action of an external electric field to account for the highly anisotropic electric polarizability. When inert salt or excess sulfonic acid is added, these compounds seem to accumulate within the aggregates and influence the attractive forces. This is generally leading to an elongation of the aggregates and, in the case of added salts, even to a marked reduction of birefringence.