Synthesis and characterization of thermally stable and/or conductive polymers.

Abstract

Eight new thermally stable polyimides were synthesized from two tricyclic heterocyclic diamines: thionine which has a phenothiazine moiety and proflavine which has an acridine unit. These processable polymers were synthesized using either a two step polyamic acid intermediate pathway or by a single step high temperature condensation reaction. The chosen route was dependent upon the system requirements. These polymerization reactions were optimized with respect to solvents, reaction time, reaction temperature, solid contents, etc., and their structure property relationships were studied. All these soluble polyimides have nice film forming properties. One of the polyimides containing the acridine moiety, appears to have a tendency to form a liquid crystalline state when its solution is passed through a fine capillary. Computer simulations on all these polyimides of degree of polymerization 10, in the absence of solvent, indicated that all of these rigid polyimides have the tendency to form a helix. Some of these helical structures contained an empty core through the structure. All of these polyimides were thermally stable in air up to 500-550$\sp\circ$C and up to 600$\sp\circ$C in a nitrogen atmosphere. They have refractive indices in the range of 1.65 to 1.85 and have relatively low value of permittivity. Two other thermally stable polymers, viz., polybenzimidazole and the ladder polymer having the phenazine moiety in the backbone were also synthesized. For these polymerization reactions, tetraamino derivative of phenazine was synthesized from the commercially available diamino, dinitro derivative of benzene. The polybenzimidazole was prepared via the azomethine pathway. This polymer had an intrinsic viscosity of 0.94 in methanesulfonic acid. The nice film forming polybenzimidazole polymer was found to be thermally stable up to 400$\sp\circ$C. The ladder type of polymer was synthesized by condensation polymerization between tetraaminophenazine and dihydroxybenzophenone in polyphosphoric acid at an elevated temperature. The completely conjugated ladder polymer was found to be semiconducting on doping with iodine. The polymer formed a nice film from methanesulfonic acid. This polymer was highly crystalline as demonstrated by its X-ray diffraction pattern. A morphology study of the polymer indicated that the material has a tendency to form dendritic crystals. The polymer was thermally stable up to about 400$\sp\circ$C in air.