Fluxional Monomers Remodel Crystallinity at Low Loadings in Diketopyrrolopyrrole Co‐Thienothiophene Conjugated Polymers

Conjugated polymers (CPs) are a class of semiconducting materials in which electrical conductivity and mechanical extensibility can coincide. Despite advances in synthesis and processing, these key properties are typically negatively correlated and derive from the semicrystalline microstructure of the polymer film. Here, we introduce a new strategy to improve the microstructure and mechanical properties of CPs through the introduction of bullvalene‐based fluxional comonomers, in which bonds rearrange constantly at ambient temperatures. By comparing bullvalene‐containing poly(diketopyrrolopyrrole‐thienothiophene) (p(DPP‐TT)) with static controls, we show that fluxional backbones resist thermal annealing induced crystallization, creating smaller crystallites even at low comonomer loadings (5 mol%). While comonomers produce minimal mechanical differences in low‐molecular weight CPs, when the network is reinforced through crosslinking, bullvalene strongly enhances stretchability, yielding a crack onset strain more than twice that of the controls. Additional experiments indicate that crosslinking enables the network to realign micro crystallites under stress to delay crack onset, but only when large crystallites are absent, as in fluxional CPs. Despite the incorporation of non‐conjugated comonomers, electrical mobility remains similar to controls at all levels of strain. This work demonstrates that fluxional components can outperform static analogues as structural modifiers in diketopyrrolopyrrole co‐thienothiophene CPs, leading to significant macroscopic effects.