Synthesis of rodlike polyhydrocarbons

Stiff macromolecules are obtained by combining two aromatic units, either directly or by vinylene or ethynylene. The palladium‐catalyzed synthesis of poly(1,4‐phenylenevinylene), poly(1,4‐phenyleneethynylene), and poly‐p‐phenylene is described. Side reactions influencing the rodlike structure are investigated by model reactions. Phenyl‐substituted poly‐p‐phenylene is obtained starting from phenyl‐1,4‐dibromobenzene. This is a solution and melt processable polymer that is stable up to 600°C. By anionic polymerization of 2‐phenyl‐1,3‐cyclohexadiene a precursor polymer with Mw/Mn = 1,1 can be obtained with molecular weights up to 30 000. By aromatization, poly(phenyl‐1,4‐phenylene) with a narrow molecular weight distribution is obtained. All of these polymers show thermotropic behaviour. Poly(1,4‐pyridinium salts) are a new class of polymers. They are rodlike polycations. With large gegenions they are soluble in organic solvents.