Surfactant-Free Preparation\nof Conjugated Polymer\nNanoparticles in Aqueous Dispersions Using Sulfate Functionalized\nFluorene Monomers

Conjugated polymer nanoparticles (CPNs) can be synthesized\nby a\nSuzuki–Miyaura cross-coupling miniemulsion polymerization to\ngive stable dispersions with a high concentration of uniform nanoparticles.\nHowever, large amounts of added surfactants are required to stabilize\nthe miniemulsion and prevent the aggregation of the nanoparticles.\nRemoval of the excess surfactant is challenging, and residual surfactant\nin thin films deposited from these dispersions can reduce the performance\nof optoelectronic devices. We report a novel approach to prepare stable\ndispersions with no added surfactant using a fluorene monomer, 2,7-dibromo-9,9-bis­(undecanesulfate)-9<i>H</i>-fluorene, with alkyl side chains terminated by negatively\ncharged sulfate groups. This functionality mimics the structure of\none of the most commonly used surfactants, sodium dodecyl sulfate\n(SDS). This charged monomer effectively stabilizes the miniemulsion\nthrough electrostatic repulsion without the use of any additional\nsurfactant in molar ratios ranging from 2.0 to 20.0 mol % of total\nmonomer content for the preparation of poly­(9,9-dioctylfluorene) (PFO)\nand poly­(9,9-dioctylfluorene-<i>alt</i>-bithiophene) (PF8T2).\nIncorporation of 5.0 mol % of the amphiphilic monomer gave stable\ndispersions with a surface potential below −40 mV and, and\npolymers with molar mass (<i>M</i><sub><i>n</i></sub>) above 10 kg mol<sup>–1</sup>. This method should be\ngenerally applicable to the preparation of dispersions of polyfluorenes\nfor application in organic electronic and optoelectronic devices without\nthe requirement for time-consuming processes to remove residual surfactant.