Synthesis and properties of new fluorinated ester,thioester, and amide substituted polythiophenes. Towards superhydrophobic surfaces

A series of new fluorinated polythiophenes has been synthesized by oxidative chemical and electrochemical polymerization and by Ullmann coupling. The substitution with the perfluoroalkyl alkyl chain CH₂CH₂C₆F₁₃ on the 3 position of the thiophene ring is performed via an ester, thioester, or amide connector, (CH₂)_m‐C(O)X, m = 0–2, with a view to investigating the role of the linker on the polymerization and on the properties of the corresponding polymers. The bromination of the monomers at the 2 and 5 positions allows the use of Ullmann coupling to form soluble fluorinated oligomers. The electron affinity was determined from cyclic voltammetry and a value of 3.1 eV was found for the ester derivative; such materials represent interesting candidates for use in light‐emitting devices or as an electron accepting material in photodiodes/solar cells. The oxidative polymerizations need the connector to be spaced out from the heterocycle to reduce its withdrawal effect. The ester, thioester, and amide spacer determined to a large extent the efficiency of the oxidative polymerization, and particularly the electropolymerization, as well as the solubility of the polymers formed. All the polymers were analyzed by GPC and by UV–visible and fluorescence spectroscopies. The electrochemical oxidation of the thioester and amide group prevents the formation of electroactive films by electropolymerization. But in the case of the ester group, the electroformed polymer exhibits exceptional stable superhydrophobic and lipophobic properties because of a porous surface and the presence of a fluorinated chain that confers low surface energy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4707–4719, 2007     

Synthesis and characterization of a new acceptor (n‐type) fluorinated and terminal‐functionalized polythiophene

Donor‐ or acceptor‐substituted polythiophenes have many potential applications in optoelectronics. Fluorinated polythiophenes are particularly attractive because of the presence of fluorine, which can withdraw electrons and also improve polymer chemical stability. Because of the promising future of these polymers, there has been much interest in identifying favorable synthetic routes to new fluorinated monomers and polymers. In this study, the monomer had an electron‐withdrawing fluorinated ester and was derived from 3‐thiophene carboxylic acid and 2,2,3,3,4,4,4‐heptafluoro‐1‐butanol. The synthesis of an n‐type fluorinated and terminal‐functionalized polythiophene was accomplished with the Ullmann coupling reaction. A polymer soluble in tetrahydrofuran was obtained with a molecular weight of approximately 15,000 g/mol. In solution, it exhibited a band gap of 2.4 eV, and the photoluminescent excitation and emission maxima were 370 nm and 555 nm, respectively. All peaks were bathochromically shifted when they were measured in the solid state. The glass‐transition and decomposition (in air) temperatures were 129 and 493 °C, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4280–4287, 2005     

Correlating Molar Mass, π-Conjugation,and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5 nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.     

Potentiometric response of poly(3-octylthiophene), poly(3-methylthiophene) and polythiophene in aqueous solutions

The potentiometric response of some polythiophenes in aqueous solutions has been investigated. Polythiophene (PT), poly(2,2'-bithiophene) (PBT), poly(3-methylthiophene) (PMT), poly(3-octylthiophene) (POT) and poly(4,4'-dioctyl2,2'-bithiophene) (POTd) were electrochemically deposited on platinum in 0.1M LiBF(4)-propylene carbonate solution containing the corresponding monomer or dimer. Polymer electrodes were also prepared by solution casting of chemically synthesized poly(3-octylthiophene) (POTc) dissolved in chloroform. After film deposition (electrochemical or chemical) the polymer coated electrodes were used as indicator electrodes in potentiometric measurements. The open-circuit potential of the polymer electrodes was measured in aqueous solutions containing inorganic salts (10(-1)-10(-4)M). Interestingly, all the polythiophenes studied were found to give a cationic response to monovalent cations such as H(+), Li(+), Na(+), K(+) and NH(+)(4) (Cl(-) salts). The slope, calculated from the linear part of the response curve, was found to depend on the polythiophene used but always remained lower than that predicted for a Nernstian response. The polythiophenes also showed some sensitivity to divalent cations such as Mg(2+) and Ca(2+) (Cl(-)-salts). POT was used as the polymer to study the influence of the polymerization conditions on the potentiometric response. By investigating different polymers from the polythiophene family it was possible to evaluate how the starting material (monomer or dimer) and the presence of alkyl side-chains influence the potentiometric response of the polymer membranes.     

ELECTRONIC EFFECTS OF POLYFLUORINATED SUBSTITUENTS ON THE POLYMERIZATION AND THE PROPERTIES OF POLYTHIOPHENES

Three series of polythiophenes containing fluoroalkoxy and fluoroether substituentswere prepared by electrochemical polymerization. The effect of substituents with fluoro-alkoxy or ether functional groups on the electrochemical polymerization of thiophene mono-mers and properties of the obtained polymers were analyzed. The introduction of a flu-oroether functional group at the 3-position of the thiophene ring leads to an increase ofthe oxidation potential of the monomer and to a decrease of the conductivity of the re-sulting polymers, even with the use of a CH_2 group as spacer. Conversely, the presenceof an oxygen atom directly at the 3-position of the thiophene ring, which offsets the nega-tive withdrawing effect of fluoroalkyl groups, facilitates the synthesis of highly conductingpolythiophenes.     

Fluorinated bis(phenoxy-imine) Ti complexes with MAO: Remarkable catalysts for living ethylene and syndioselective living propylene polymerization

Based on new results as well as the reported data, the ethylene and propylene polymerization behavior of bis(phenoxy-imine) Ti complexes (Ti-FI Catalysts) combined with MAO (particularly that of their fluorinated versions) is discussed, with an emphasis on the characteristics and mechanisms of living ethylene and syndioselective living propylene polymerization. Unlike common living olefin polymerization catalysts, fluorinated Ti-FI Catalysts with MAO display thermally robust living behavior and polymerize ethylene in a highly controlled manner at temperatures as high as 50 °C. Additionally, despite being C₂-symmetric catalysts, fluorinated Ti-FI Catalysts/MAO mediate highly syndioselective living propylene polymerization. Fluorinated Ti-FI Catalysts that we developed are the first examples of catalysts that induce the living polymerization of both ethylene and propylene. In addition, they are also the first examples of living and, at the same time, highly stereoselective propylene polymerization catalysts. The versatile and robust living nature of the fluorinated Ti-FI Catalysts allows the preparation of a wide variety of unique living polymers; some of which can even be produced catalytically. On the basis of theoretical calculations as well as experimental results, we conclude that these unusual polymerization features of fluorinated Ti-FI Catalysts originate from an attractive interaction between the ligand and a growing polymer chain and/or the fluxional character of the catalyst coupled with 2,1-regiochemistry. This is in stark contrast to group 4 metallocene catalysts, which control olefin polymerization mainly by repulsive interactions based on the rigidly organized ligand frameworks.     

Radical polyaddition reaction of bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate onto diformylalkane

Radical polyaddition of bis(α-trifluoromethyl-β,β-difluorovinyl) terephthalate [CF₂C(CF₃)OCOC₆H₄COOC(CF₃)CF₂] (BFP) with diformylalkanes to produce fluorinated polymer bearing ketone-carbonyl groups in main chain is described. The radical additions of hexanal, pentanal and benzaldehyde with 2-benzoxypentafluoropropene [CF₂C(CF₃)OCOC₆H₅] were examined as model reactions to yield the corresponding addition product with hexanal and pentanal in high yields, and no product with benzaldehyde. The addition of acyl and hydrogen was found to take place to perfluoroisopropenyl group. The results of the model reactions suggested that the reaction might be applicable to polyaddition to produce polymers with diformylalkanes. The results of polyaddition of BFP with glutaraldehyde under the emulsion polymerization condition showed that the polymer of M_n=4.8×10³ was obtained in fairly high yields. This might be a novel preparation method of polymers bearing fluorinated polyketone structure.     

Bandgap Engineering through Controlled Oxidation of Polythiophenes

The use of Rozen’s reagent (HOF?CH₃CN) to convert polythiophenes to polymers containing thiophene‐1,1‐dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3‐alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60 % TDO moieties in the polymer backbone. The resulting polymers have a markedly low‐lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well‐defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.     

Polythiophenes via thiophene, bithiophene and terthiophene in propylene carbonate: an electrochemical and in-situ FTIR study

Polythiophene films obtained by the galvanostatic polymerization of thiophene (Th), bithiophene (BTh) and terthiophene (TTh) in 0.5 M LiClO₄ + propylene carbonate have been investigated by cyclic voltammetry and in-situ Fourier transform IR (FTIR) spectroscopy. The polymerization potential in the propylene carbonate electrolyte decreases in the order Th BTh TTh. Both the charge capacity and the doping level of the resulting polymers increase in the order polythiophene (PTh) < polybithiophene (PBTH) polyterthiophene (PTTh). For PTTh, a doping level of 37% is obtained during cycle 10 and 31% during cycle 1000.In-situ FTIR spectra of the neutral PBTh and PTTh films show a single band at 3063 cm⁻¹ (corresponding to aromatic β-(C---H)-groups) which suggests a regular α,α′-linking of the monomeric units. For thin PTh films the intensity of this band is very weak, indicating a disordered cross-linked polymer structure. During the electrochemical oxidation of the three polythiophenes investigated from 3.3 V up to 4.4 V vs. Li/Li⁺ the intensity of the electronic absorption band (above 2000 cm⁻¹) increases with increasing potential, but it strongly decreases at potentials above about 4.4 V, indicating a strong irreversible oxidation of the polymer films. Furthermore, strong CO₂ evolution is observed at potentials above 4.2 V.     

Kumada chain-growth polycondensation as a universal method for synthesis of well-defined conjugated polymers

Kumada chain-growth polycondensation (KCGP) is a novel method for the synthesis of well-defined conjugated polymers. Because the Ni-catalyst can transfer in an intramolecular process to the propagating chain end, the polymerization follows chain-growth mechanism. With this newly developed method, various conjugated polymers, such as polythiophenes, poly(p-phenylene) (PPP), polypyrrole (PPy), and polyfluorene with controlled molecular weights and relatively narrow polydispersities (PDIs), have been prepared. Especially, the polymerizations for poly(3-alkylthiophene)s (P3ATs), PPP, and PPy exhibited quasi-living characteristics, which allows preparing polymer brushes, fully-conjugated block copolymers, and macroinitiators and macro-reactants for the synthesis of rod-coil block copolymers. In the current review, the progress in this new area is summarized.     

Nanostructure dependence of field-effect mobility in regioregular poly(3-hexylthiophene) thin film field effect transistors

Low polydispersity regioregular polythiophenes with number average molecular weights ranging from 2 to 13 kDa were cast under the same conditions from solution to form a series of field effect transistors (FETs). Tapping mode AFM and grazing incidence small-angle X-ray scattering revealed that in all cases the polymers formed regular nanofibrillar morphologies with the width of nanofibrils proportional to the weight average contour length of polymer chains, indicating that conjugated backbones were oriented perpendicular to the nanofibril axes. FET charge carrier mobilities exhibited exponential dependence on nanofibril width, pointing to the decisive role of extended conjugated pathways in charge transport.     

New regiosymmetrical dioxopyrrolo- and dihydropyrrolo-functionalized polythiophenes

[structure: see text] We present the synthesis of two N-alkylated poly(dioxopyrrolothiophene)s and two N-alkylated poly(dihydropyrrolothiophene)s with potential application in the field of conducting polymers. The polymers are synthesized from the corresponding 2,5-dibromothiophenes by an Ullmann-type polymerization and a Stille-type polymerization, respectively. The two N-alkylated poly(dihydropyrrolothiophene)s are the first examples of amino-functionalized polythiophenes built from regiosymmetrical thiophene monomers.     

Novel fluorinated poly(aryl ether ketone)s

Two novel fluorinated monomers were prepared and polymerized with biphenols to produce amorphous, thermally stable poly(aryl ether ketone)s. The properties of the fluorinated polymers are compared to those of unfluorinated, amorphous poly(aryl ether ketone)s. The presence of fluorine in the polymers was found to cause a decrease in glass transition temperature and Young's moduli, however, no increase in thermal stability was observed. The fluorinated polymers are soluble in common organic solvents such as chloroform and methylene chloride at room temperature, and also show solubility in solvents containing a ketonic moiety, such as acetone. Evidence of polymer branching through fluorines considered to be unreactive under the polymerization conditions was found. Efforts were made to evaluate the reactivity of fluorine atoms under the polymerization conditions using both molecular modeling and ¹⁹F-NMR to ascertain if such branching could be avoided. © 1995 John Wiley & Sons, Inc.     

Surface active semifluorinated diblock copolymers prepared by group transfer polymerization

Diblock copolymers consisting of poly(methyl methacrylate) and poly(2-perfluorobutylethyl methacrylate) with narrow molecular weight distribution have been synthesized by group transfer polymerization. Different ratios of the PMMA block to the fluorinated block have been prepared. It was found that all polymers are surface active. Critical micelle concentrations are not dependent on the fluorinated block length. Critical surface tensions, extrapolated from Zisman plots and the dispersion force component of the surface energies extrapolated from Girifalco-Good-Fowkes-Young plots were decreasing with increasing length of the fluorinated block.     

Effect of block length on the self-assembly of end-capping perfluoroalkyl moieties on the polymer surface

Most research on copolymers with fluorinated monomers has focused on the relationship between fluorinated monomer content and the corresponding surface structure. However, the influence of the non-fluorinated block on the surface structure of the copolymer film is unknown. Various molecular weight poly(butyl methacrylates) (PBMA) end-capped with 2-perfluorooctylethyl methacrylate (FMA) units (PBMA-ec-FMA) have been synthesized by atom transfer radical polymerization (ATRP). The effect of the PBMA block length on the surface structure and properties of the polymers both in the solid state and in solution was investigated using various techniques. X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy and X-ray diffraction (XRD) analyses indicated that longer PBMA blocks enhanced both the enrichment of the fluorinated moieties and the order of the packing orientation of the perfluoroalkyl side chains on the surface. This enhancement was attributed mainly to the molecular aggregate structure of the end-capped polymers with long PBMA blocks in the solution and to the interfacial structure at the air/liquid interface, which favors the -(CF₂)₇CF₃ moieties self-assembling on the polymer surface during film formation. This observation suggests that the polyacrylate block structure in fluorinated diblock copolymers, in addition to the fluorinated monomer content, plays an important role in structure formation on the solid surface.     

MALDI-ToF analysis of polythiophene: use of trans-2-[3-(4-t-butyl-phenyl)-2-methyl- 2-propenylidene]malononitrile-DCTB-as matrix

Nowadays, numerous experimental and theoretical studies are devoted to the research field of polythiophenes and other electroconjugated polymers due to the huge potentialities of those conducting polymers. Synthetic procedures are now developed to reach the highest control over both polymerization and analytical methodologies allowing an in-depth and straightforward characterization of the polymer samples without any required doubt. Mass spectrometry methodologies and in particular MALDI-ToF measurements are definitively suitable to meet the characterization requirements. In the present study, trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) was shown to afford better results than the reported terthiophene and dithranol matrices as far as sensitivity and signal-to-noise ratio are concerned. We tentatively proposed that the ionization of the P3HT molecules is performed by charge exchange in the condensed phase (clusters) with matrix molecule radical cations and subsequent neutral matrix molecule evaporation from the clusters. The putative key parameters to account for the really high efficiency of DCTB for the MALDI analysis of P3HT are (1) the highest ionization energy of DCTB amongst the three matrices, (2) the really high absorptivity of the matrix molecule at the laser wavelength and (3) the presence of the tertiobutyl group on the matrix molecule. The presence of this substituent is likely to decrease the intermolecular interactions in the condensed phase rendering the evaporation of the neutral matrix molecules less energy demanding. We also demonstrated for polymer samples presenting an average number molecular weight (M(n) ) below 10 000 g mol(-1) that the systematic overestimation of the low mass oligomers upon MALDI measurements ends up with wrong M(n) and polydispersity index (PDI) values. A systematic Soxhlet extraction against heptane was shown to allow the recording of absolute M(n) and PDI.     

Microemulsion polymerization for producing fluorinated structured materials

When perfluoropolyether microemulsions are used during polymerization of fluoropolymers, the structure of the reaction environment can be strictly controlled. In particular, the number and size of polymer particles in latexes can be set freely, yielding a number of advantages. First, as a result of radical segregation, terminations can be decreased without reducing polymerization rate: in this way high molecular weights are easily obtained also with poorly reactive monomers. Moreover, in combination with a reversible chain transfer mechanism based on iodine, particle segregation allows establishing pseudo-living polymerization conditions. In this situation formation of long branches in the polymer can be controlled by using bifunctional molecules that are able to link two different polymer chains to each other during polymerization. This is the so-called “branching and pseudo-living” technology. Finally, by co-coagulating latexes of different polymers prepared by microemulsion polymerization, very small particles and, thus, high interface areas are generated. In this way properties of different polymers, such as fluoroelastomers and fluorinated semicrystalline polymers, are matched effectively, generating new nanocomposite materials that exhibit outstanding properties. In this paper these results are reported and an overview of some novel sophisticated fluoropolymers obtained in microemulsion is given.     

Frontispiece: Dehalogenative or Deprotonative? The Preparation Pathway to the Organometallic Monomer for Transition-Metal-Catalyzed Catalyst-Transfer-Type Polymerization of Thiophene Derivatives

Due to a wide range of applications in electronic materials, polythiophenes attract considerable attention in organic and polymer syntheses as well as in materials science. For the purpose of developing the practical synthetic protocol, this review focuses on the deprotonative pathway in the preparation of thiophene organometallic monomer, which was shown to be effective employing 2-halo-3-substituted thiophene as a monomer precursor. The thus metallated thiophene monomer was shown to undergo polymerization by nickel(II) complex catalysis, with which highly regioregular head-to-tail (HT)-type polythiophenes were obtained with controlled molecular weight and molecular weight distribution. Several polythiophene derivatives with modified thiophene-ring and side-chain structures were shown to be designed in order to achieve the designed functionality as materials.     

Topotactic solid-state polymerization of 3-aminocrotonamide by radiation

Radiation-induced solid-state polymerization of 3-aminocrotonamide (3-amino-2-butenamide) was carried out at room temperature, in open air atmosphere and under vacuum condition. The polymer obtained was white powder, soluble in methanol, but insoluble in water. The nature of polymers were investigated by IR, UV, x-ray, DP-MS, and elemental analysis to elucidate the mechanism of the polymerization. The polymer was crystalline with melting point in the range of 245–255°C. The cell parameters and space group of monomer and polymers were determined from powder x-ray diffraction patterns. The similarity of crystal structures of monomer and polymer indicated a topotactic polymerization. It was shown by spectroscopic investigations and elemental analyses that the polymerization proceeds by condensation reaction with evolution of one mole ammonia per two combined moles of monomer through a free radical mechanism. © 1996 John Wiley & Sons, Inc.     

In Situ Hetero End‐Functionalized Polythiophene and Subsequent “Click” Chemistry With DNA

It is demonstrated that bifunctionalized polythiophenes involving thiol and azide end‐functional groups can be synthesized by chain‐growth Suzuki‐Miyaura type polymerization. The bifunctionalized polythiophenes are successfully characterized by 1H NMR, gel permeation chromatography (GPC), and matrix‐assisted laser desorption ionization time‐of‐flight (MALDI‐TOF). Furthermore, the azide end‐group reacts with DNA via “click chemistry” to form a polythiophene/DNA hybrid structure, which is characterized by ESI‐MS. The described synthetic approaches will lead to the synthesis of novel multi‐block copolymers as well as biomolecule‐based conjugated polymer structures.