(255f) Donor-Acceptor Fully Conjugated Block Copolymers through Chain-Growth Polymerizations

Donor-acceptor fully conjugated block copolymers are composed of covalently bonded donor and acceptor conjugated polymers. Donor-acceptor block copolymers are a promising candidate in photovoltaics due to their ability to microphase separate at length scales commensurate with exciton diffusion lengths. Conjugated block copolymers can also serve as model systems to study the relationship between molecular structure, microstructure, and optoelectronic properties of conjugated polymers. The most widely used synthetic route for conjugated block copolymers is the polymerization of the donor block by Grignard metathesis (GRIM), followed by chain extension through a Stille or Suzuki-Miyaura polycondensation to grow the acceptor block. Due to the step-growth mechanism, this approach leads to a mixture of products including homopolymers, muliblock copolymers, as well as diblock copolymers. To minimize the formation of these impurities, different approaches are required such as synthesis of both blocks through chain-growth polymerizations. We prepared poly(3-hexylthiophene-2,5-diyl)-block-poly((2,6-bis(thiophene-2-yl)naphthalene-1,4,5,8-tetracarboxylic-N,Nâ?²-bis(2-octyldodecyl) diimide)- 5â?²,5â?³-diyl) (P3HT-b-PTNDI) through chain-growth polymerizations. After synthesis of P3HT by GRIM, the second block, PTNDI, was polymerized through a chain-growth mechanism in a condensation polymerization using active zinc. Chain extensions were tracked by NMR as a function of the reaction time, and formation of block copolymers was confirmed by GPC using a UV-vis detector. These well-defined donor-acceptor conjugated block copolymers are expected to serve as good model systems for studies of self-assembly in semiflexible copolymers and photophysical properties of donor-acceptor systems.