Conjugated polymers (CPs) have been incorporated into a range of applications such as photovoltaics, transistors, diodes, and sensors. To successfully integrate CPs into organic electronics, conjugated polymers must maintain high charge transport and high mechanical robustness. However, current conjugated polymers usually suffer from low fracture strains and poor performance after stretching. Optimizing both mechanical properties and charge transport remains a challenge. One strategy is to modify side chains of CPs. In this work, we investigated the incorporation of ester groups in the side chains of poly(3-alkylthiophenes)(P3AT). P3ATs are CPs with simple synthesis, good electrical properties but are very brittle. Since ester groups can act as plasticizers, we hypothesized that their incorporation into side chains of P3ATs would increase the polymer’s stretchability. A series of poly(3-hexylthiophenes(P3HT) and poly(3-dodecylthiophenes) (P3DDT) copolymers with varying ratio of ester-functionalized side chains (1:1, 3:1, 4:1, and 8:1 alkyl to ester) were synthesized and characterized. Incorporation of the ester group in the middle of the side chains prevents decomposition at the ester linkage. Absorption spectra of copolymers with high ester content (1:1) lack the vibronic shoulders normally observed in P3HT and P3DDT films; pointing to some disruption in intermolecular packing. This was also observed in X-ray diffraction. It was found that the copolymers were more ductile with lower Elastic’s modulus compared to the literature values for P3HT and P3DDT. Disruption in intermolecular packing resulted in lower mobilities of the P3AT derivatives compared to P3HT standard with similar molecular weights, however, still within the same magnitude. This result shows rational design of polymer chemical structures can improve mechanical properties while maintaining charge transport in P3ATs.

Effect of ester-functionalized side chains on mechanical and electronic properties of poly(3-alkylthiophenes) copolymers

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