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Komber H.,Leibniz Institute fur Polymerforschung Dresden e.V. | Senkovskyy V.,Leibniz Institute fur Polymerforschung Dresden e.V. | Tkachov R.,Leibniz Institute fur Polymerforschung Dresden e.V. | Johnson K.,University of Cambridge | And 4 more authors.

Interactions of Ni(0) and thiophene-benzothiadiazole-thiophene (TBT) units during the Kumada catalyst transfer polycondensation (KCTP) of 2-chloromagnesio-5-bromo-3-hexylthiophene (1) are investigated. Monofunctional TBT initiator precursors are used for the external initiation of KCTP, and the mechanism of initiator activation and polymerization is elucidated using NMR and MALDI-ToF MS. We find that the activation of the TBT-bromide initiator precursor using nickel-diethylbipyridine (NiEt 2bipy) occurs via a two-step pathway, in which NiEt 2bipy coordinates to benzothiadiazole (B) first, followed by the elimination of butane and oxidative addition of liberated Ni(0)bipy into the terminal TBT-Br bond. It is shown that the B unit traps Ni(0) during the KCTP of 1, which results in significant termination, as derived from the degree of bromine-terminated chains. The ability of B units to trap Ni(0) is further illustrated by using a symmetric bifunctional Br-TBT-Br initiator precursor for the KCTP of 1, during which Ni(0) is not able to "ring walk" over the B unit to initiate polymerization at the other end of the chain. These results are important for the design of well-defined and electronically end-functionalized conjugated polymers, but also for understanding termination mechanisms in KCTP in general. © 2011 American Chemical Society. Source

Williams P.E.,Melville Laboratory for Polymer Synthesis | Williams P.E.,University of Warwick | Moughton A.O.,Melville Laboratory for Polymer Synthesis | Moughton A.O.,University of Warwick | And 4 more authors.
Polymer Chemistry

Until recently, the primary controlled radical polymerization (CRP) technique used to synthesize side chain semi-conducting block copolymers from vinyl monomer species has been nitroxide-mediated polymerization (NMP). The potential exploitation of reversible addition fragmentation chain transfer (RAFT) polymerization for the preparation of semi-conducting diblocks has not yet been fully realized. In this work a trithiocarbonate chain transfer agent (CTA) has been shown to polymerize both hole transporting (HT) monomers m-vinyltriphenyl amine and p-vinyltriphenyl amine and also a new fluorinated triphenylamine monomer for the first time, affording both homopolymers and diblock copolymers with good control over molecular weight (Mn) and narrow polydispersities (Mw/Mn). The electronic properties of these blocks and diblocks were explored using UV-vis and cyclic voltammetry analysis. The selective self-assembly of these diblocks into solution nanostructures has been explored and characterized by DLS and TEM analysis. © The Royal Society of Chemistry 2011. Source

Kohn P.,University of Cambridge | Huettner S.,University of Cambridge | Komber H.,Leibniz Institute of Polymer Research | Senkovskyy V.,Leibniz Institute of Polymer Research | And 9 more authors.
Journal of the American Chemical Society

Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl 2 as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl 2-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well. © 2012 American Chemical Society. Source

Sommer M.,Melville Laboratory for Polymer Synthesis | Sommer M.,Albert Ludwigs University of Freiburg | Komber H.,Leibniz Institute of Polymer Research | Huettner S.,University of Cambridge | And 5 more authors.

We present the synthesis, purification, and characterization of all-conjugated block copolymers comprising poly((9,9-dioctylfluorene)-2,7-diyl- alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (PF8TBT) and poly(3-hexylthiophene) (P3HT). Suzuki step-growth polycondensation is used for the synthesis of PF8TBT, which is subsequently terminated via the addition of narrow-distributed, monobrominated P3HT-Br. Purification via preparative GPC is carried out to reduce polydispersity and to remove excess P3HT. Wavelength-dependent GPC and careful NMR end group analysis, assisted by model compounds, reveal pure diblock copolymers of PF8TBT-b-P3HT. Insight into structure formation is given by temperature-dependent UV-vis absorption, DSC, and X-ray scattering. These indicate that PF8TBT-b-P3HT does not microphase-separate within the investigated range of composition and molecular weight. The critical role of introducing sufficient dissimilarity between the segments in all-conjugated block copolymers in order to induce phase separation is discussed, with the conclusion that careful tuning of side chains is crucial for achieving self-organization. © 2012 American Chemical Society. Source

Brinkmann M.,Charles Sadron Institute | Gonthier E.,Charles Sadron Institute | Bogen S.,Charles Sadron Institute | Tremel K.,Institute For Polymerchemie | And 4 more authors.
ACS Nano

Highly oriented films of an electron accepting polymer semiconductor, poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl] -alt-5,5′-(2,2′-bithiophene)} (PNDI2OD-T2), are obtained by two different methods, namely directional epitaxial crystallization (DEC) on 1,3,5-trichlorobenzene (TCB) and epitaxy on friction transferred poly(tetrafluoroethylene) (PTFE) substrates. Two distinct polymorphs with unprecedented intrachain resolution are identified by high-resolution transmission electron microscopy (HR-TEM). Form I is obtained by DEC on TCB, whereas highly oriented films of form II are obtained on PTFE substrates after melting at T = 300 °C and cooling at 0.5 K/min. In form I, both electron diffraction and HR-TEM indicate a segregated stacking of bithiophene (T2) and naphthalene diimide (NDI) units forming separate columns. In form II, a ∼c/2 shift between successive π-stacked chains leads to mixed π-overlaps of T2 and NDI. Form I can be transformed into form II by annealing at T > 250 °C. The different π-stacking of NDI and T2 in the two polymorphs have characteristic signatures in the UV-vis spectra, especially in the charge transfer band around 750 nm which is also observed in spin-coated films. © 2012 American Chemical Society. Source

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