Benzyl bromide functionalized poly(phenyleneethynylene)s: A novel approach toward conjugated polymers with a well-defined chemical reactivity

The palladium(0)-copper(I)-catalyzed polymerization of 1,4-diethynyl-2,5-bis(decyloxy)benzene (I), 1,4-bis(2-ethylhexyloxy)-2,5-diiodobenzene (IIA), 1-(6-(4-(hydroxymethyl)phenoxy)hexyloxy)-2,5-diiodo-4-methoxybenzene (III), and iodobenzene (IV) yielded a highly soluble, exclusively para-linked poly(phenyleneethynylene) (PPE2A). Thereby, statistically every fourth phenyleneethynylene unit bore a benzyl alcohol group predetermined by the molar ratio of the monomers. The monofunctional monomer IV was used as molar mass limiter, since preliminary investigations on the polymerization of I and IIA had revealed that the solubility of alkoxy-substituted poly(phenyleneethynylene)s consisting of more than 40 phenyleneethynylene units decreases drastically. The maximum effective conjugation length was attained at approximately 12 phenyleneethynylene repeating units. Furthermore, a partially meta-linked benzyl alcohol functionalized poly(phenyleneethynylene) (PPE2B) was synthesized employing 1,3diiodobenzene (1111) instead of IIA. Both conjugated polymers (PPE2A and PPE2B) could be converted quantitatively into benzyl bromide functionalized poly(phenyleneethynylene)s (PPE3A and PPE3B) applying triphenylphosphine and tetrabromomethane. Comparison of the polymers by means of GPC and UV/vis spectroscopy before and after the bromination showed no significant differences and thus no impairment of the delocalized pi-electron system.