Poly-(3-hexylthiophene) bottlebrush copolymers with tailored side-chain lengths and high charge carrier mobilities†
A series of well-defined poly(3-hexylthiophene) (P3HT) grafted bottled brushes PS-g-P3HT with different P3HT chain lengths were synthesized by a grafting-to approach using nitroxide mediated controlled radical polymerization. The influence of the side-chain length on the optical, thermal and electronic properties of these polymers is systematically studied and compared with the corresponding linear P3HTs. It can be shown that the optical, structural and electronic properties of the brushes depend heavily on the side chain lengths. The results of DSC, UV-Vis and AFM measurements reveal two important things. The brush polymers with low molecular weight P3HT side-chains do not crystallize and therefore exhibit very poor electronic properties. With an increase of the side-chain length, highly crystalline materials are obtained and a brush with a high molecular weight (144 kg mol−1) carrying long P3HT side chains (17 000 g mol−1) is necessary to obtain crystalline lamellar structures and the best charge transport properties. For the first time P3HT brush polymers are reported that can match the excellent electronic properties of their linear counterparts in the range of 10−2 cm2 V−1 s−1. Additionally, the brush polymers exhibit better thin film stability at elevated temperatures compared to linear P3HTs.