Alkoxide-Initiated Regioselective Coupling of Carbon Disulfide and Terminal Epoxides for the Synthesis of Strongly Alternating Copolymers

The synthesis of highly regioregular and alternating polythiocarbonates from carbon disulfide and terminal epoxides has been achieved. The copolymerizations were performed under ambient and solvent-free conditions in the presence of LiO^<i>t</i>Bu (0.125–0.5 mol %) as initiator. At higher loadings the reaction pathway switched in favor to the catalytic formation of cyclic dithiocarbonates. Under optimized reaction conditions polymers with molecular weights up to 109 kg mol^–1 were isolated. The NMR spectroscopic analysis of the polythiocarbonates revealed that 94% of backbone structure is formed by strongly alternating head-to-head arrangement of epoxypropane and 1,2-epoxybutane monomers, respectively, at a thiocarbonate group −CHR–OC­(S)­O–CHR– and tail-to-tail arrangement at a trithiocarbonate group −CH₂–SC­(S)­S–CH₂–. Atactic polymers were obtained using racemic mixtures of the epoxides, but an isotactic polymer was obtained when chiral (<i>R</i>)-epoxy­propane was converted. A mechanism is proposed which rationalizes the regio- and stereochemistry observed for the alkoxide-initiated copolymerization of CS₂ and terminal epoxides

One-Pot Synthesis of All-Conjugated Block-Like Bisthiophene–Naphthalenediimide/Fluorene Copolymer

A copolymerization of electron-rich and electron-deficient monomers via the chain-growth catalyst-transfer polycondensation route is highly challenging and has never been accomplished thus far, to the best of our knowledge. Herein, we report a simple method to copolymerize two monomers of a significantly different nature: anion-radical naphthalene diimide–dithiophene-based and zinc-organic AB-type fluorenic ones. We found that the copolymerization proceeds rapidly in the presence of Pd catalyst having the bulky and electron-rich tri<i>-tert</i>-butylphosphine ligand. Despite the fact that the two monomers are simultaneously added to the copolymerization (batch polymerization), the polymerization leads to a gradient or even block-like copolymer rather than to a random copolymer or to a mixture of homopolymers, as evident from NMR, GPC, AFM, and fluorescence quenching experiments. The block-like copolymer is formed because the fluorenic monomer polymerizes much faster, yet because the resulting PF2/6 homopolymer is able to initiate polymerization of the second monomer, presumably acting as macroinitiator. Although the investigated copolymerization does not involve a living propagation mechanism and the resulting product is not a well-defined block copolymer, this result is an important step toward a general protocol for preparation of all-conjugated donor–acceptor block copolymers for optoelectronic applications

Methacrylate Copolymers with Liquid Crystalline Side Chains for Organic Gate Dielectric Applications

Polymers for all-organic field-effect transistors are under development to cope with the increasing demand for novel materials for organic electronics. Besides the semiconductor, the dielectric layer determines the efficiency of the final device. Poly­(methyl methacrylate) (PMMA) is a frequently used dielectric. In this work, the chemical structure of this material was stepwise altered by incorporation of cross-linkable and/or self-organizing comonomers to improve the chemical stability and the dielectric properties. Different types of cross-linking methods were used to prevent dissolution, swelling or intermixing of the dielectric e.g. during formation processes of top electrodes or semiconducting layers. Self-organizing comonomers were expected to influence the dielectric/semiconductor interface, and moreover, to enhance the chemical resistance of the dielectric. Random copolymers were obtained by free radical and reversible addition–fragmentation chain transfer (RAFT) polymerization. With 6-[4-(4′-cyanophenyl)­phenoxy]­alkyl side chains having hexyl or octyl spacer, thermotropic liquid crystalline (LC) behavior and nanophase separation into smectic layers was observed, while copolymerization with methyl methacrylate induced molecular disorder. In addition to chemical, thermal and structural properties, electrical characteristics like breakdown field strength (<i>E</i>_BD) and relative permittivity (<i>k</i>) were determined. The dielectric films were studied in metal–insulator–metal setups. <i>E</i>_BD appeared to be strongly dependent on the type of electrode used and especially the ink formulation. Cross-linking of PMMA yielded an increase in <i>E</i>_BD up to 4.0 MV/cm with Ag and 5.7 MV/cm with PEDOT:PSS electrodes because of the increased solvent resistance. The LC side chains reduce the ability for cross-linking resulting in decreased breakdown field strengths

Influence of Semiconductor Thickness and Molecular Weight on the Charge Transport of a Naphthalenediimide-Based Copolymer in Thin-Film Transistors

The N-type semiconducting polymer, P­(NDI2OD-T2), with different molecular weights (MW = 23, 72, and 250 kg/mol) was used for the fabrication of field-effect transistors (FETs) with different semiconductor layer thicknesses. FETs with semiconductor layer thicknesses from ∼15 to 50 nm exhibit similar electron mobilities (<i>μ</i>’s) of 0.2–0.45 cm² V^–1 s^–1. Reduction of the active film thickness led to decreased <i>μ</i> values; however, FETs with ∼2 and ∼5 nm thick P­(NDI2OD-T2) films still exhibit substantial <i>μ</i>’s of 0.01–0.02 and ∼10^–4 cm² V^–1 s^–1, respectively. Interestingly, the lowest molecular weight sample (P-23, MW ≈ 23 kg/mol, polydispersity index (PDI) = 1.9) exhibited higher <i>μ</i> than the highest molecular weight sample (P-250, MW ≈ 250 kg/mol, PDI = 2.3) measured for thicker devices (15–50 nm). This is rather unusual behavior because typically charge carrier mobility increases with MW where improved grain-to-grain connectivity usually enhances transport events. We attribute this result to the high crystallinity of the lowest MW sample, as confirmed by differential scanning calorimetry and X-ray diffraction studies, which may (over)­compensate for other effects