Poly(p-phenylene Vinylene) Nanoparticles by Acyclic Diene Metathesis (admet) Polycondensation in Aqueous Emulsion

Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Germany Introduction Poly(p-phenylene vinylene) (PPV) and its derivatives are amongst the most widely studied class of conjugated polymers since the discovery of their electroluminescent properties in 1990. These polymers are studied for applications in numerous photonic devices such as organic solar cells, organic light emitting diodes (OLEDs), but also in field-effect transistors and electrochemical cells. 3 Nanoparticles of conjugated polymers may contribute to resolve the manifest issue of processing this class of polymers. Aqueous polymer dispersions are of interest in this context, as printing techniques are compatible with aqueous systems, and water is a non-solvent for most polymers. Beyond the traditional free-radical emulsion polymerization applied industrially, catalytic polymerization in aqueous emulsion has evolved as a general route to polymer nanoparticle dispersions. However, a prerequisite are sufficiently water-insensitive catalysts. Numerous synthetic routes towards PPV have been elaborated. Postpolymerization of precursor polymers or direct polymerization to PPVs by various methods, including olefin metathesis reactions, have been reported. The facile availability of monomers and the marginal occurrence of side products and defects makes olefin metathesis a useful synthetic tool in PPV synthesis. PPV with regularly alternating cisand transvinylene linkages can be accessed by chain-growth ROMP of [2.2]paracyclophane-1,9diene. Step-growth acyclic diene metathesis (ADMET) polycondensation of p-divinylbenzenes results in defect-free materials bearing all-trans-vinylene units. 10 Recently, we demonstrated the ADMET polycondensation of 1,4dipropoxy-2,5-divinylbenzene in aqueous emulsion with Ru alkylidene catalysts affording PPV nanoparticles as a bright red latex. In step-growth polymerizations, the catalyst leaves the polymer chain after each addition of a repeat unit, making the active species particularly susceptible towards water. The active metal site is stabilized by chelating κ-O coordination of the alkoxy moiety in alkylidene species formed from the monomer, similar to the coordination environment in the robust and moisture-insensitive catalyst precursor 2. A small portion of the water-sensitive catalyst remains active for several days. We report the step-growth metathesis polymerization of 1,4-dialkylsubstituted divinylbenzene by Ru metathesis catalysts in aqueous emulsion to afford PPV nanoparticles. [(PCy3)(η-C-C3H4N2Mes2)Cl2Ru=CHPh] (1, “Grubbs second generation”) and [η-C-C3H4N2Mes2){κ-=CH-o(PrO)C6H4}RuCl2] (2, “Hoveyda-Grubbs second generation”) were employed as catalyst precursors for the ADMET polycondensation of 1,4-bis(2’ethylhexyl)-2,5-divinylbenzene (3). Additional polymerizations were carried out in homogeneous organic phase for comparison.