Base-free Suzuki polymerization for the synthesis of polyfluorenes functionalized with carboxylic acids

A carboxylic acid-functionalized conjugated polyelectrolyte (CPE) was synthesized by Suzuki polymerization using basic reagents to activate the boronic acid/ester to undergo the catalytic cycle and to form the aryl-aryl bond. The polymerization employed the dibromide and diboronate ester of two fluorene derivatives that were subsequently polymerized. The polymerization of these monomers was tested under a variety of conditions with cesium fluoride (CsF) and tetrabutylammonium fluoride (TBFA) used as a fluorine source. The results show that diester-functionalized polyfluorene (PF-DE) is converted to its diacid form (PF-DA) by hydrolyis in refluxing dioxane and recovered by acidifying the solution and collecting the precipitate. The absorption band maximum of PF-DA in a basic solution is red-shifted and PF-DA exists in an aggregated state in methanol and water.