Towards rigid‐rod polyelectrolytes via well‐defined precursor poly(paraphenylene)s substituted by 6‐iodohexyl side chains

Abstract A synthetic strategy is presented which opens up an efficient access to readily soluble poly( para ‐phenylene) (PPP) electrolytes of well‐defined molecular constitution and conveniently determinable degree of polycondensation ( DP ). By means of PPP derivatives substituted by carboxylic acid functionalities, a four‐step precursor route has been developed which consists of (a) the Pd‐catalyzed synthesis of PPPs with 6‐phenoxyhexyl pendant groups, followed by (b) the cleavage of the 6‐phenoxyhexyl ethers using trimethyliodo silane. The latter conversion produces exclusively 6‐iodohexyl pendant groups, the reaction of which with sodium 4‐ethylcarboxylatophenolate (c), followed by ester hydrolysis (d) yielded the desired rigid‐rod polyelectrolytes. Under appropriate reaction conditions all steps (a–d) occur highly selectively and almost quantitatively, and no degradation of the polymer backbone occurs, as is shown by high resolution NMR spectroscopy and osmometric investigations. Thus, structurally homogeneous carboxylated PPPs of well‐known DP are available by that reaction sequence. Essentially, this success is due to the excellent solubility of all intermediates involved as well as the advantageous reactivity of the 6‐iodohexyl‐substituted PPP intermediate.