Synthesis, Phase Behavior, and Semiconductor Properties of Siloxane Copolymers Containing Grafted C8-BTBT Units

Synthesis and characterization of a series of novel graft copolymers based on siloxane backbones containing 50%, 20%, and 10% of laterally attached π-conjugated [1]benzothieno[3,2-b][1]benzothiophene (BTBT) units are presented. The copolymers were synthesized via hydrosilylation reaction of linear poly(methylhydrosiloxanes) of varying functionality with alkenyl-functionalized 2-octyl-7-(undec-10-en-1-yl)-BTBT. Comprehensive investigations by DSC, TGA, and synchrotron SAXS/WAXS revealed that at room temperature all the copolymers synthesized form crystalline phases with layered structures, where both the phase-transition temperatures and the layer thickness strongly depend on the grafting density. As the grafting density decreases, the fraction of crystallizable side chains is reduced, leading to an increase in the amorphous component. Their semiconductor properties were preliminarily elucidated in organic field-effect transistors fabricated via spin-coating, which showed the hole mobilities in the range of 1.6 × 10^-4 to 2 × 10^-2 cm²V^-1s^-1 depending on the grafting density of BTBT units to the polysiloxane main chain. These are the first graft copolymers containing BTBT side chains possessing semiconductor properties comparable to those of π-conjugated linear copolymers. These findings establish grafted polysiloxanes as a promising platform for developing solution-processable, high-performance organic semiconductors.