NUCLEAR-MAGNETIC-RESONANCE STUDIES ON ELECTROCHEMICALLY PREPARED POLY(3-DODECYLTHIOPHENE)

Soluble and electrically conductive poly(3-dodecylthiophene) (PDDT) films were prepared by means of electrochemical polymerization of 3-dodecylthiophene. We observed the H-1 and C-13 NMR spectra of PDDT in chloroform-d. The resonances of the 4-protons on the successive 2,5-linked thiophene rings are resolved into four peaks, which arise from different triad sequences due to the alignment of monomers. With the aid of H-1-H-1 NOESY and H-1 NOE difference spectroscopy for PDDT, the configurational structures were determined. A pair of doublet peaks at delta = 6.93 and 7.16 are assigned to the 4- and 5-protons on the terminal 2-substituted 3-dodecylthiophene rings, and peaks attributable to the other terminal units were not detected. The fractions of the sequences and the end-group analysis reveal the mechanism for the propagation of the electrochemical polymerization of 3-dodecylthiophene. The diad and triad fractions are accounted for in terms of Bernoulli statistics. The 3-dodecylthiophene monomer is proved to be attacked predominantly at the 2-position of the thiophene ring with a probability of 82% in spite of the terminal configuration. The relative intensity of the peaks ascribable to the terminal unit and the results on the mechanism of the propagation suggest that the degree of polymerization of PDDT is 140.