Abstract
Polystyrene-b-poly(3-hexylthiophene) (PS-b-P3HT) block copolymers with fixed PS
block length have been synthesized by combined atom transfer radical polymerization (ATRP) and
Grignard metathesis (GRIM) polymerization. The self-assembled structures of these diblock
copolymer thin films based on PS-b-P3HT have been studied by TEM, SAED, GIXD, AFM, and
additionally by first principles modeling and simulation. These block copolymers undergo
microphase separation and form nanostructured spheres, lamellae, nanofibers, or nanoribbons in
the films dictated by the molecular weight of the P3HT block. Within the diblock copolymer thin film,
PS blocks segregate to form amorphous domains, and the covalently bonded conjugated P3HT blocks exist as highly ordered crystalline domains through intermolecular packing with their alkyl side chains aligned normal to the substrate while the thiophene rings align parallel to the substrate
through π π stacking. The conjugated PS-b-P3HT block copolymers exhibited significant
improvements in organic field-effect transistor (OFET) performance and environmental stability
as compared to P3HT homopolymers, with up to a factor of 2 increase in measured mobility
(0.08 cm2/(V 3 s)) for the P4 (85 wt % P3HT). Overall, this work demonstrates that the high degree of molecular order induced by block copolymer phase separation can improve the transport properties and stability of conjugating polymers, which are critical for high-performance OFETs and other organic electronics.
