Architectural Effects on Solution Self-Assembly of Poly(3-hexylthiophene)-Based Graft Copolymers

While solution assembly of conjugated block copolymers has been widely used to produce long 1-D nanowires (NWs), it remains a great challenge to provide a higher level of control over structure and function of the NWs. Herein, for the first time, we report the solution assembly of graft copolymers containing a conjugated polymer backbone in a selective solvent and demonstrate that their self-assembly behaviors can be manipulated by the molecular structures of the graft copolymers. A series of poly(3-hexylthiophene)-graft-poly(2-vinylpyridine) (P3HT-g-P2VP) copolymers was designed with two different architectural parameters: grafting fraction (f_g) and molecular weight of P2VP chains (M_n,P2VP) on the P3HT backbone. Interestingly, crystallization of the P3HT-g-P2VP copolymers was systematically modulated by changes in f_g and M_n,P2VP, thus allowing for control of the growth kinetics and curvatures of solution-assembled NWs. When M_n,P2VP (4.4 to 15.1 kg/mol) or f_g (2.8 to 9.2%) of the P3HT-g-P2VP polymers was increased, the crystallinity of the copolymers was reduced significantly. Steric hindrance from the grafted P2VP chains apparently modified the growth of NWs, leading to shorter NWs with a greater degree of curvature for graft copolymers with more hindrance. Therefore, we envision that such conjugated chain-based graft copolymers can be versatile building blocks for producing NWs with controlled length and shape, which can be important for tailoring the optical and electrical properties of NW-based devices.