Single-chain polymerization dynamics and conformational mechanics of conjugated polymers

Summary Conjugated polymers possess unique optoelectrical properties. Characterizing their synthesis and mechanical processability is crucial for tailored applications. Their poor solubility presents a universal challenge, however. Here, we report a single-molecule study, which circumvents the solubility challenge, of the polymerization kinetics and conformational mechanics of polyacetylene, a prototypical conjugated polymer. We monitor the growth of individual long-chain polyacetylenes during ring-opening metathesis polymerization of cyclooctatetraene. We discover that polyacetylene forms nonequilibrium conformational entanglements, whose kinetic instability and structural looseness appear to render its polymerization more facile than that of polycyclooctene, a nonconjugated analog. This relative kinetics is contrary to monomer reactivity predictions. Moreover, even under identical solvent conditions, individual polyacetylenes show diverse extension-versus-force scaling behaviors; many span multiple scaling regimes predicted previously but never observed. The extracted persistence and Kuhn length of polyacetylene are also significantly shorter than its wavefunction delocalization length, indicating that polyacetylene can maintain backbone conjugation while staying flexible.