Effect of Solvent Quality and Sidechain Architecture On the Conjugated Polymer Chain Conformation In Solution

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Polymer Science and Engineering


Conjugated polymers (CPs) are solution-processible for various electronic applications, where solution aggregation and dynamics could impact the morphology in the solid state. Various solvents and solvent mixtures have been used to dissolve and process CPs, but few studies quantify the effect of solvent quality on the solution behaviors of CPs. Here, we performed static light scattering, small-angle X-ray scattering, combined with molecular dynamics (MD) simulation, to investigate CPs solution behaviors with various solvent quality, including poly(3‐alkylthiophene) (P3ATs) with various sidechain lengths from -C4H9 to -C12H25, poly[bis(3-dodecyl-2-thienyl)-2,2'-dithiophene-5,5'-diyl] (PQT-12) and poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-12). We found that chlorobenzene is a better solvent than toluene for various CPs. It is evident from the majority positive second virial coefficient A2 ranging from 0.3 to 4.7 ×10-3 cm3*mol/g2 towards P3ATs. For P3ATs in non-polar solvents, longer sidechains promote more positive A2 and thus signaling a better polymer-solvent interaction, where in toluene A2 increases from -5.9 to 1.4 ×10-3 cm3*mol/g2 and in CB A2 ranges from 1.0 to 4.7 ×10-3 cm3*mol/g2 when sidechain length increases from -C6H13 to -C12H25. Moreover, PQT-12 and PBTTT-12 have strong aggregation tendencies in all the solutions, with an apparent positive A2 (~0.5 ×10-3 cm3*mol/g2) due to multi-chain aggregates and peculiar chain folding. These solvent-dependent aggregation behaviors can be well correlated to spectroscopy measurement results. Our coarse-grained MD simulation results further suggested that CPs with longer, dense, and branched sidechain can achieve enhance polymer-solvent interaction, and thus enable overall better solution dispersion. Our work here provides quantitative insights into the solution behavior of conjugated polymers that can guide both the design and process of CPs toward next-generation organic electronics.

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