Kinetic Study of the Knoevenagel Condensation Applied to the Synthesis of Poly[bicarbazolylene-alt-phenylenebis(cyanovinylene)]s

The Knoevenagel condensation has been applied to the synthesis of [bicarbazolylene- alt -phenylenebis(cyanovinylene)] copolymers and their model compounds. The kinetic study at 65 °C showed a very complex reaction: the apparent order was found to change with the modification of experimental conditions. In methanol the reaction rate is governed by the dissociation step of the active methylene compound (step 1 of the reaction mechanism). In THF/MeOH mixtures, the rate-determining step is a result of the relative rate ratio step 1/step 2. The influence of several dipolar interactions between the active methylene compounds, the aldehyde monomers, and the solvents used is discussed along with the effects of the polarity and the concentration of comonomers on reaction rates. More importantly, the possibility to control precisely the reaction rate via the appropriate choice of the dielectric constant of the initial medium is emphasized. Finally, the observed results obtained have been transposed to the synthesis of wholly THF-soluble conjugated copolymers, which can reach molecular weight equal to 25 000, in polystyrene equivalent.