Enhanced thermoelectric and mechanical performance of fully conjugated block polythiophene modified with polar ethylene glycol side chains/single-walled carbon nanotube composite materials†

Composite materials comprised of conductive polymers and single-walled carbon nanotubes (SWCNTs) hold substantial research significance in the field of thermoelectric materials. The design of side chains plays a critical role in conjugated polymers to achieve superior thermoelectric properties of composite materials. In this study, we synthesized a series of block copolymers composed of poly(3-octylthiophene) (P3OT) and poly(3-(2,5,8,11-tetraoxadodecyl)thiophene) (P3TEGT), designated as P3OT-b-P3TEGT with three distinct block ratios (2 : 1, 1 : 1, and 1 : 2 of conductive segment P3OT to polar segment P3TEGT). Then we combined these block copolymers with SWCNTs to prepare stretchable and bendable composite films. We found that when the optimal mass ratio of SWCNTs was 90%, mechanically, the higher the proportion of the P3TEGT polar segment correlated with lower tensile strength and Young's modulus of the composite films, demonstrating more flexible stretching properties. Thermoelectrically, the higher proportion of the P3TEGT segment resulted in an increased hole concentration in the composite films. The composite with a 2 : 1 block ratio and 90% SWCNT content, labeled as 1 : 2/SWCNTs-0.9, showed the best thermoelectric performance with a conductivity of 1206.03 S cm⁻¹ and a power factor of 189.67 μW m⁻¹ K⁻², which exceeds the performance of pure SWCNTs in both thermoelectric performance and flexibility. These findings suggested that manipulating the proportion of polar side chains in conjugated polymers can significantly enhance the thermoelectric and mechanical properties of composite materials. We believe that this study will lay the groundwork for a molecular design strategy aimed at developing new flexible thermoelectric materials, and expand the potential applications of such composites in future technology.