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Overview

π-Conjugated (semiconducting) polymers is an important class of materials for various optoelectronic applications ranging from solar cells, field transistors and light-emitting diodes to energy storage devices and sensors. Semiconducting polymers are generally produced by relatively poorly controlled step-growth polymerizations.

We develop alternative polymerization approaches, so-called catalyst-transfer polycondensations of AB-type monomers in which growth of polymer chains occur as a one-by-one addition of monomers to initiator species. With this polymerization mechanism, reproducible preparation of well-defined conjugated polymers becomes straightforward. Furthermore, synthesis of more complex polymer architectures, such as polymer brushes, hairy particles, gradient and block copolymers, is possible in many cases. Utilization of such nanostructured materials in heterojunction optoelectronic devices should be beneficial where precise control of nanomorphology is crucial. kiriy group

External initiation of Kumada-polycondensation was developed, for the first time, which allows preparation of conjugated polymers with specific starting groups. The method implies reaction of Ni(0) complexes with aryl halides. Further polymerization induced with thus-forming initiator leads to the transfer of aryl group to the polymer structure.

A method to synthesize the second generation of externally addable Ni initiators supported by state-of-the art bidentate phosphorous ligands (e.g., dppe, dppp) was developed. It implies reaction of NibipyEt2 with aryl halides followed by replacement of N-based bipy ligand onto P-based ones.  This initiation method was found to be very universal (works with wide variety aryl halides including strongly electron-deficient ones) and efficient (high yield of the transfer of aryl groups to polymers).

Figure 1. A universal method for external initiation of Kumada catalyst-transfer polycondensation.

The third method which uses sterically hindered aryl halides (i.e., ones having alkyl substituents ortho- to Br- or Grignard functions) was developed for very convenient preparation of the initiators from easily available and stable compounds (e. g., NidppeCl2 and aryl Grignards).

Figure 2. Preparation of Ni-initiators from Ni(dppp)Cl2 and sterically hindered Grignard followed by polymerization of hexylthiophene.

References

  • Kohn, P.; Huettner, S.; Komber, H.; Senkovskyy, V.; Tkachov, R.; Kiriy, A.; Friend, R.; Steiner, U.; Huck, W. T. S.; Sommer, J.-U.; Sommer, M.
    On the role of single regiodefects and polydispersity in regioregular poly(3-hexylthiophene): Defect distribution, synthesis of defect-free chains, and a simple model for the determination of crystallinity. Journal of the American Chemical Society 134 (2012) 4790-4805 more
  • Komber, H.; Senkovsky, V.; Tkachov, R.; Kiriy, A.; Huck, W. T. S.; Sommer, M.
    Ring walking versus trapping of nickel(0) during kumada catalyst transfer polycondensation using externally initiated electron-accepting thiophene-benzothiadiazole-thiophene precursors. Macromolecules 44 (2011) 9164-9172 more
  • Senkovsky, V.; Sommer, M.; Tkachov, R.; Komber, H.; Huck, W. T. S.; Kiriy, A.
    Convenient route to initiate kumada catalyst-transfer polycondensation using ni(dppe)CI2 and sterically hindered grignard compounds. Macromolecules 43 (2010) 10157-10161 more