Topochemical polymerization of monomers with conjugated triple bonds

Abstract Solid‐state polymerization of monomers with conjugated triple bonds turns out to be a versatile method for synthesis of crystalline polymers of high molecular weight exhibiting a fully conjugated backbone. The reaction is best described as an 1.4‐addition polymerization of the conjugated triple bonds giving rise to a polymer with three cumulated double bonds per repeating unit. The all‐trans configuration of the substituents is a consequence of the solid‐state reaction mechanism and is already predetermined by the packing of the molecules in the monomer lattice. It was shown by X‐ray analysis in the case of poly(2.4‐hexadiin‐1.6‐diol‐bis‐phenylurethane) that the polymer diacetylenes can be described by either a butatriene structure or by a mesomeric en‐in‐structure. magnified image Polymerization of the colorless monomer crystals is achieved by irradiation with UV‐ or high‐energy radiation or by simply annealing the monomer crystals below their melting point. Deep red, blue or black polymer crystals are obtained exhibiting strong dichroism with the fibre axis as the direction of main absorption. These crystals possess semiconducting properties (E A = 0.6–1.0 eV, depending on the substituents at the conjugated backbone).