Conductive polymers promise to serve as lightweight, flexible electronic devices. We envision that such devices could be accessed via convenient solution processing methods and rolled or folded for ease of storage. However, the mechanical demands of rolling or folding are actually quite great, and require a material that is tough and deforms elastically, even after many cycles of deformation. Unfortunately, little work has been done to actually understand the mechanical properties of these materials, even in well-characterized conductive polymers such as the ubiquitous poly(3-hexylthiophene) (P3HT). Recently, some work has been done to address this chasm. Researchers have estimated the modulus of regioregular P3HT through various extrapolation methods, and the result is a stiff, but brittle material. In reality, most conductive polymers are highly ordered and crystalline, which gives rise to good electronic properties, but would not allow the flexible devices envisioned.<br/><br/>Here, we report the bulk mechanical properties of regioregular poly-3(alkylthiophenes) (P3ATs) as measured at room temperature by dynamic mechanical analysis (DMA). We find that as side chain length increases, polymer ductility increases, but conductivity, mobility, and stiffness decrease. In search of a conductive polymer with superior electronic and mechanical properties, we synthesized a series of random copolymers of P3ATs and unsubstituted thiophene, incorporating thiophene monomers in a 3:1 and 1:1 ratio. The unsubstituted thiophene should enhance the electronic properties, as well as the stiffness of the material, and its random incorporation should increase disorder, making the semi-crystalline material more amorphous, hopefully increasing the its toughness. The 3:1 random copolymers were found to have increased conductivity (150, 400, and 300 S/cm, respectively for 3:1 P3HT, P3OT, and P3ddT) and mobilities on par with that of P3HT (0.07 cm<sup>2</sup>/Vs). Remarkably, these polymers are more ductile and also 620, 760, and 430% tougher than their respective homopolymers. This is an interesting example of how introducing competing molecular factors can allow us to engineering a conductive polymer with superior mechanical and electronic properties.

Enhancing the mechanical and electronic properties of poly(3-alkylthiophenes) through random copolymerization

251st National Meeting (2016)

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