Elucidating and Expanding the Monomer Scope with Heterogeneous Catalysis in Direct Arylation Polymerization (DArP)

While providing a more sustainable method of conjugated polymer synthesis with advantages over other cross-coupling methods, direct arylation polymerization (DArP) is still reliant on expensive, single-use homogeneous Pd catalysts. Previously, we have demonstrated the compatibility and recyclability of the commercially available heterogeneous catalyst SiliaCat DPP-Pd with DArP for the synthesis of poly[(3,4-ethylenedioxythiophene-2,5-diyl)-(9,9-dioctylfluorene-2,7-diyl)] (PEDOTF). Here, we demonstrate the compatibility of this catalyst across a broader range of monomers, including electron-deficient 2,2′,3,3′,5,5′,6,6′-octafluorobiphenyl and dithienyldiketopyrrolopyrrole (DPP), as well as 3-hexylthiophene and hexyl thiophene-3-carboxylates at 100 °C. Polymers were afforded with molar masses up to 40 kg/mol in yields up to 97%. These reactions also showed good compatibility with SiliaCat, which was able to be recycled up to five times with catalyst recoveries of 80–90%. Investigations of the room-temperature synthesis of PEDOTF using SiliaCat showed reduced reactivity using K3PO4, but using K2CO3, polymers of up to 11.1 kg/mol were achieved, and the catalyst was recycled five times. Investigations of the negative impact of K3PO4 across a range of monomers for polymerizations at 100 °C revealed similar detrimental effects, except for 2-bromo-3-hexylthiophene and 2-bromo-3-hexylesterthiophene, which performed similarly with K3PO4 and K2CO3. These findings provide insight into the compatibility of a broad range of monomers and reaction conditions with heterogeneous catalysis, as relevant to improving the accessibility and scalability of polymerizations using DArP.