Molecular weight dependence of the physical properties of protonated polyaniline films and fibers.

Polyaniline, (PANI) in the form of emeraldine base (figure 1), was synthesized by polymerizing aniline in acid solutions at different sub-zero temperatures to give a range of molecular weights between 100,000 and 300,000 gmol(-1). Molecular weights were measured using gel permeation chromatography (GPC). The polymers were formed into solvent-cast films using an acid processing technique, involving 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) as the solvating/protonating acid group and dichloroacetic acid (DCA) plus formic acid (FA) as the solvent. The dried, free-standing films were stretched by drawing over a hot pin to align the polymer chains. Fibers were prepared by spinning more concentrated solutions into a butanone coagulation bath. Conductivity measurements were then made on the drawn films and fibers, and tensile test measurements performed to determine the peak stress and modulus of the drawn films and fibers. The reaction conditions under which the different polyanilines were synthesized, and their molecular weight, were found to have a definite effect upon both the electrical and mechanical properties of the drawn films and fibers. The drawn films and fibers can be used as mechanical actuators.