The acid-catalysed polycondensation of 2-acetoxymethylthiophenes. Kinetics and mechanisms

Unravelling the detailed microstructure of a semiconducting (quasi‐metal) soluble polymer incorporating conjugated thienylene methine sequences

“…Figures 7 and 8 show typical 1 H and 13 C NMR spectra of polymers isolated long after complete monomer conversion. It is important to emphasize that the numerous spectra of polymers prepared with different catalysts, different solvents, and different reaction times15–17 displayed systematically the same qualitative features as those appearing in Figures 7 and 8, albeit with modestly variable relative intensities.…”

“…The formation of the S B branching site is rationalized either in a similar way as for S A , but with the methine site of a B unit, or through the successive loss in the acidic medium of a hydride ion and a proton from the S A structure (as in the mechanism described above generating B from A 15–18), as shown in Scheme .…”

“…Sequences A are generated by the “normal” 2,5‐thienylene methylene enchainment arising from the successive electrophilic substitutions between the activated acetate moiety of a growing chain and the hydrogen atom at the C5 position of a monomer molecule. These units are the precursors of sequences B through the successive loss of a hydride ion from a bridging methylene group, and of a proton, from the neighboring CH 2 15–18 leading to the conjugated sequences consisting of aromatic‐type units alternating with the exounsaturated thiophene counterparts.…”

“…In all the H − /H + loss cycles, the hydride ions associate with the methylene end group of the active species to give unreactive methyl groups ( 1 H NMR peak at 2.3 ppm, Fig. 7), whereas the protons join the acetate moiety to give acetic acid 15–18…”

“…We recently studied the polycondensation of a series of thiophene‐methylene (ThCH 2 ) monomers bearing an acetate moiety15–17 and discovered that the ensuing macromolecules displayed two major types of sequences, namely, the expected nonconjugated repetition of 2,5‐thienylene methylene units A (Fig. 1) and conjugated counterparts alternating aromatic‐type 2,5‐thiophene and quinoid‐type exounsaturated 2,5‐thiophene moieties joined by a methine bridge B (Fig.…”