Electronic and Ionic Transport in Processable Conducting Polymers. SymmetryEffects on the Physical and Electrically Conducting, Substituted Poly(di-2-thienylphenylenes)

摘要

Effect of symmetry on the physical and electronic properties of a series ofconjugated polymers composed of di(2 thienyl) 2,5 disubstitutedphenylene repeat units, symmetrically and asymmetrically substituted with methoxy, heptoxy, dodecyloxy, hexadecyloxy, eicosinoxy and hexyl groups were studied. Polymers were prepared via an oxidative polymerization using ferric chloride and isolated after dedopping with ammonium hydroxide. Neutral polymers, soluble in common organic solvents including chloroform, methylene chloride and tetrahydrofuran, are predominantly linked at the 5 and 5' positions of the thiophene rings to result in fully conjugated main chains that are stable to 360 C under nitrogen. Molecular weight analyses indicate weight average degrees of polymerization of ca. 10-20; thus, substantial fraction of chains in each sample contains 30-50 aromatic rings. Differential scanning calorimetry studies revealed that melt transitions, indicative of molecular ordering, are present in the symmetrically substituted polymers. Order found in these polymers was confirmed by x-ray diffraction and found to persist at elevated temperatures, yielding birefringent melts, suggestive of liquid crystalline order. Asymmetrically substituted polymers found to be amorphous. Upon oxidation of the insulating polymers, bipolaronic charge carriers were formed with the oxidized polymers exhibiting electrical conductivities up to 4/ohms cm.