Recycling Heterogenous Catalysts for Multi-Batch Conjugated Polymer Synthesis via Direct Arylation Polymerization

Abstract

Despite the inherent sustainability direct arylation polymerization (DArP) offers through a C−H activation pathway, the use of expensive homogeneous Pd catalysts remains problematic for large-scale conjugated polymer (CP) synthesis. Herein, the first report on the recycling of heterogeneous catalysts for CP synthesis using DArP is presented. We found SiliaCat Pd-DPP to be a highly efficient and recyclable catalyst for multi-batch CP synthesis providing CPs with molecular weights (M n ) up to 82 kg/ mol even after being recycled three times. Batch-to-batch variations were further optimized to afford up to five batches of polymers with a M n of 25 ± 2.5 kg/mol without structural disparity. Significantly, this work discloses among the most sustainable CP synthesis protocols to date and presents the critical concept of catalyst-recycling to the important field of organic semiconducting polymers, which potentially enables access to truly low-cost flow chemistry for industrial-scale CP synthesis.

Combining flow synthesis and heterogeneous catalysis for the preparation of conjugated polymers

“…We noted that the batch reaction was performed under ideal reaction conditions (5 mol% Pd/C with a monomer concentration of 0.03 M) as reported. 34–37 Both reactions were conducted three times, and we demonstrated the high reproducibility of molecular weight and Đ with very small errors between runs (9.8% for M n and 15.5% for Đ ) using our flow system (Table 1), compared to much larger errors in batch synthesis (24.1% for M n and 13.4% for Đ ) (Table S2†). In the flow reaction, the resulting PTB7 exhibited an average M n of 8.2 kDa and a broad Đ of 3.29 with two distinct peaks in GPC traces.…”

“…[21][22][23][24] Using a heterogeneous catalyst is attractive as the catalyst is easily separable from the product, meaning that no additional purification processes are required, and it is easy to handle with high air stability and cost-effectiveness. [25][26][27][28][29][30][31][32][33][34][35][36][37] In the field of organic semiconductors, Pd catalyzed cross-coupling reactions, including the Stille, Suzuki-Myaura, and Heck couplings, have been successfully conducted for small molecule synthesis and reported with high yields. For conjugated polymer synthesis, few studies have been reported as well and they have clearly demonstrated the benefits of having a high purity polymer product with a low Pd residue when a heterogeneous catalyst was used.…”

“…For conjugated polymer synthesis, few studies have been reported as well and they have clearly demonstrated the benefits of having a high purity polymer product with a low Pd residue when a heterogeneous catalyst was used. [34][35][36][37] For example, Chen and co-workers conducted cross-coupling polymerization using the heterogeneous catalyst Pd/C, and synthesized a diketopyrrolopyrrole (DPP) based copolymer and the polymer with a number average molecular weight (M n ) of 14.5 kDa. 35 The resulting polymer had only 34 ppm of Pd residue, which is 100 times lower than that obtained when the homogeneous catalyst Pd(PPh 3 ) 4 was used, and exhibited one order of magnitude higher hole mobility in field-effect transistors.…”

Shape and stability matter: enhanced catalytic reactions via sol-gel entrapped catalysts

“…In late 2021, Thompson and co-workers reported that SiliaCat DPP-Pd can be successfully employed in the direct arylation polymerization for the large-scale and green synthesis organic semiconducting polymers. 1 The catalyst, an ORMOSIL functionalized with diphenylphosphine ligands bound to Pd(II) in which every Si atom is bound to the C atom of a methyl group, 17 was found to be highly efficient and recyclable affording polymers with molecular weights up to 82,000 g/mol.…”

Direct Arylation Polycondensation of β-Fluorinated Bithiophenes to Polythiophenes: Effect of Side Chains in C–Br Monomers

“…The investigations are mainly focused on the DArP of different C–H monomers − and can be classified into two categories. One is applying well-known aromatic units in the construction of CPs, for example, 2,2′-bithiophene (BT), − thieno­[3,4- c ]­pyrrole-4,6-dione (TPD), ,− and 3,4-dioxythiophene (DOT), ,− as C–H monomers, and the DArP conditions are optimized to yield CPs with higher molecular weights, ,,,− less structural defects, ,,,,− and better sustainability. ,,,,− The other is designing new C–H monomers to attain high DArP activity and CPs with promising optoelectronic properties simultaneously. − β-Halogenated thiophene derivatives are typical examples of this type of C–H monomers. ,,− The introduction of halogen atoms at ...…”