Synthesis of All-Conjugated Donor-Acceptor-Donor ABA-Type Triblock Copolymers via Kumada Catalyst-Transfer Polycondensation

A novel initiator, N,N'-bis(2-decyltetradecyl)-2,6-dibromonaphthalene-1,4,5,8-bis (dicarboximide) (NDI-Br-2), was found effective in the Kumada catalyst-transfer polycondensation (KCTP) for the synthesis of regioregular poly(3-hexylthiophene) (P3HT). In addition, a two-step method of synthesizing all-conjugated triblock copolymers comprised of both n-type and p-type blocks was proposed. With a 10:9 feed molar ratio of NDI-Br-2 to 2,5-bis(trimethylstannyl)thiophene, an n-type macroinitiator (PNDITh-Br-2) was prepared via the Stille coupling reaction. Two outer P3HT blocks were then emanated via KCTP initiated by PNDITh-Br-2 to produce all-conjugated ABA-type triblock copolymers. The size exclusion chromatography (SEC) curves of all the triblock copolymers showed narrow distribution, with the lowest polydispersity index (PDI) of 1.15. Moreover, the molecular weight of the block copolymer was found to be independent of the amount of Ni catalyst, while it can be tailored by the feed molar ratio of the thiophene monomer to PNDITh-Br-2. The transmission electron microscopy (TEM) images and grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns of the block copolymer thin film revealed a well-defined lamellar structure and two distinguished crystalline domains, where the P3HT layer was in the range of 10-20 nm and presented an edge-on rich alignment.