The influence of chain scission on the molecular weight of conjugated polymers in a continuous flow reactor

•Molecular weight reduction observed during PTB7 synthesis in a flow reactor.•Flow-induced chain scission of PTB7 under typical stille polycondensation conditions.•Flow degradation due to both mechanochemical and thermal phenomena.•Flow degradation is likely to be a competing side reaction in the flow polymerization. The conjugated polymer PTB7 was found to undergo flow-induced chain scission under conditions typically employed in the flow synthesis of conjugated polymers, supporting that polymer degradation is a key side reaction that can influence the molecular weight of conjugated polymers synthesized in flow. Flow synthesis is becoming an increasing important method for the rapid and reproducible synthesis of conjugated polymers with optimal molecular weight. Increasing the length of time the polymerization solution remains in the flow system (the residence time), initially leads to an increase in molecular weight, but declines are observed at longer residence times. Our results support that conjugated polymers undergo mechanochemical chain scission in flow and that reactor temperature, polymer molecular weight, and polymer concentration are important factors that influence the extent of degradation. These results should aid in the future optimization of conjugated polymer syntheses in flow.