Synthesis and Electroluminescent Properties of Disubstituted Polyacetylene Derivatives Containing Multi‐Fluorophenyl and Cyclohexylphenyl Side Groups

A new series of disubstituted polyacetylene derivatives that contain multi‐fluorine atoms on the pendent phenyl ring have been synthesized and characterized. The results reveal a greater red‐shift in UV‐vis absorption and PL emission upon incorporating more fluorine atoms on the pendent phenyl ring. Among them, disubstituted polyacetylene with a difluorophenyl group ( PDPA‐2F ) showed the highest luminescent efficiency. The device performance can be promoted by blending a hole‐transporting material TM‐TPD into PDPA‐2F as the active layer or by using a light‐emitting copolymer in which PDPA‐2F was copolymerized with a carbazole group ( PDPA‐2Fcab ). A light‐emitting diode of ITO/PEDOT/ PDPA‐2Fcab /Ca/Al revealed a maximum luminescence of 4230 cd · m^?2 at 14 V and a maximum current efficiency of 3.37 cd · A^?1 at 7 V.

     

Multilayer Films Fabricated from Oppositely Charged Polyphenylene Dendrimers by Electrostatic Layer‐by‐Layer Assembly

Summary: Assemblies of oppositely charged L ‐lysine/carboxylic acid functionalized polyphenylene dendrimers and hybrid multilayers of L ‐lysine dendrimers/colloidal gold nanocrystals were fabricated as alternate multilayers on 3‐mercaptopropionic acid coated gold surfaces via layer‐by‐layer deposition. The fabrication of the multilayer films was monitored by kinetic and scan mode surface plasmon resonance spectroscopy. The permeability properties of the dendritic polyelectrolyte layers were characterized by electrochemistry in the presence of [Fe(CN)₆]^3?/4? as the redox couple. A high interfacial charge‐transfer resistance, originating from the electrostatic repulsion of the negatively charged redox couple against the negatively charged interface was observed and the charge‐transfer resistance found to increase with increasing number of layers.

3D‐structure of the investigated polyphenylene dendrimers: a) G₂(L ‐lysine)₈ and b) G₂(COOH)₁₆.     

Spectroelectrochemical and Photovoltaic Characterization of a Solution‐Processable n‐and‐p Type Dopable Pyrrole‐Bearing Conjugated Polymer

D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

     

Segmented Block Copolymers with Monodisperse Aramide End‐Segments

Segmented block copolymers were synthesized using monodisperse diaramide (TΦT) as hard segments and PTMO with a molecular weight of 2 900 g · mol^?1 as soft segments. The aramide: PTMO segment ratio was increased from 1:1 to 2:1 thereby changing the structure from a high molecular weight multi‐block copolymer to a low molecular weight end‐block copolymer. The thermal and thermal‐mechanical properties were studied by DSC and DMA. Also studied were the tensile and the elastic properties as well as the melt rheological behavior as a function of frequency. The crystallinity of aramide in the end‐block copolymers was found to be higher than in the multi‐block copolymer.

     

Synthesis and Optical Properties of π‐Conjugated Polymers Composed of Benzo[1,2‐b:4,5‐b′]dithiophene and Thiophenes Bearing Electron‐Deficient Ethenyl Groups in the Side Chains

π‐Conjugated polymers composed of dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene and thiophenes bearing cyano‐alkoxycarbonylethenyl [? CH?C(CO₂R)CN] and bis(alkoxycarbonyl)ethenyl groups [? CH?C(CO₂R)₂] were prepared. The optical properties of the obtained polymers were investigated by UV‐vis and photoluminescence spectroscopy to demonstrate that the absorption maxima of the polymers were tunable by varying the substituent of thiophene unit. The photoluminescence wavelengths and intensities of the polymer in solution were significantly dependent on the polymer side chain. The HOMO energy level of the polymer was lowered by up to ?5.51 eV by introducing electron‐deficient cyano groups. Polymer solar cells based on the new polymers were fabricated to achieve a PCE of 1.90%.

     

Peculiar Catalytic Behavior of Poly(vinylidene fluoride) for Cationic Polymerization

Summary: A cationic polymerization of isobutylene, isobutyl vinyl ether, ethyl vinyl ether, vinylcarbazole and α‐methylstyrene was induced by mixing with poly(vinylidene fluoride) (PVDF) powder. The polymerization was an exothermic reaction and gave a high yield. An electron was abstracted from the monomer by PVDF. By the abstraction of the electron, the monomer was converted to a cation radical which induced polymerization. The generation of the cation radicals of the vinyl ethers was confirmed by an ESR spin trapping method, although the cation radicals could be coupled immediately. The resulting polymer was isolated from PVDF (not grafted) and characterized by size exclusion chromatography, IR, UV‐Vis and NMR spectroscopy. The copolymerization of vinyl ethers or vinyl ether/vinylcarbazole was carried out successfully to obtain their random copolymer. PVDF is regarded as a reusable catalyst for cationic polymerizations.

Reaction mechanism of the cationic polymerization of iBVE.     

Surface Functionalized ZnO Particles Designed for the Use in Transparent Nanocomposites

Summary: We present a new method for preparing a nanocomposite containing highly dispersed ZnO nanoparticles. The essence of this approach is the formation of surface modified inorganic particles and their homogeneous incorporation into a polymeric matrix. Therefore, an inverse emulsion of an inorganic salt, for example, zinc acetate stabilized by amphiphilic statistical copolymers, is prepared. By hydrolysis under basic conditions ZnO particles of a size below 100 nm are formed within the micelles. As the surfactant remains adsorbed on the surface of the particles, a surface functionalization with hydrophobic chains is performed. These chains can be considered as compatibilizers for blending of the ZnO nanoparticles in PMMA affording transparent nanocomposite films avoiding particle aggregated. The present approach is in principle applicable to all nanoparticles prepared in a sol‐gel process.

TEM image of redispersed ZnO particles.     

Synthesis of Defined Poly(silsesquioxane)s: Fast Polycondensation of Trialkoxysilanes in a Continuous‐Flow Microreactor

The polycondensation of trialkoxysilanes to PSSQs in a microreactor setup is demonstrated. While continuous‐flow processes involving microreactors found various applications in chain growth polymerization, their influence on step‐growth polymerization is less explored, and the polycondensation of multifunctional monomers has not been studied in detail. We found significantly increased yields and a decreased polydispersity of the obtained polymers in comparison to the batch process. By variation of the residence time molecular weights could be adjusted reproducibly ranging from = 1 900 to 11 000 g · mol^?1. Thus, the microreactor setup offers for the first time the possibility to synthesize PSSQ with adjustable properties.

     

Anisotropic Dimensional Swelling of Membranes of Ultrafine Hydrogel Fibers

Summary: Interconnecting fibrous membranes were generated by electrospinning an aqueous mixture of poly(acrylic acid) and poly(vinyl alcohol) at a 3.5 COOH/OH molar ratio. The membranes containing 200 to 500 nm diameter fibers were crosslinked by heat‐induced esterification and behaved like anionic hydrogels, i.e., they swelled significantly more at a pH above 4. The dimensional expansion of these fibrous membranes was far greater in their thickness than in their planar areas. The anisotropic dimensional expansion was associated with the spatial arrangement of fibers, i.e., much smaller inter‐fiber spaces along the thickness direction than in the planar directions. Crosslinking under constraint caused further fiber compaction in the thickness direction, leading to anisotropic and accordion‐like dimensional expansion upon swelling.

SEM image of the PAA/PVA membrane (C1) thermally crosslinked under high constraint.     

Solid‐State Olefin Metathesis: ADMET of Rigid‐Rod Polymers and Ring‐Closing Metathesis

Summary: Solid‐state olefin metathesis of rigid‐rod acyclic diene metathesis (ADMET) polymers and ring‐closing metathesis (RCM) have been investigated. 1,4‐Dipropoxy‐2,5‐divinylbenzene ( 4 ) was synthesized and used in a bulk ADMET polymerization to produce oligomers of dialkoxy poly(phenylene vinylene). The reaction was continued in the solid state, effectively doubling the molecular weight. Solid‐state RCM was investigated with a variety of solid dienes and metathesis catalysts, and demonstrated in low conversions using amide diene 5 with catalysts 9 , 13 , and 14 .

     

Towards Highly Substituted Starburst Macromolecular Semiconductors: Microwave Synthesis,Spectroscopy and Electrochemical Properties

As part of a strategy to explore highly functionalized macromolecular semiconductors, a series of highly substituted twelve‐armed macromolecules F1CzTr‐F3CzTr consisting of truxene, 9‐phenylcarbazole and oligofluorene units were synthesized. To accomplish the synthesis of twelve‐armed targets, a high yield microwave enhanced synthesis method for direct twelve‐fold Suzuki couplings was developed. The resulting materials exhibited high purity and good monodispersity (PDI 1.01–1.03). The molecular weight of the compound F3CzTr achieved 14 266 g · mol^?1, representing one of the largest well‐defined starburst conjugated molecules. The thermal, photophysical and electrochemical properties were investigated.

     

Gas‐Phase Assisted Surface Polymerization of Vinyl Monomers with Fe‐Based Initiating Systems

Summary: Gas‐phase assisted surface polymerization (GASP) of methyl methacrylate (MMA) and styrene (St) was investigated with Fe‐based radical initiating systems, FeCl₂/2,2′‐bipyridine (Bpy)/methyl α‐bromophenylacetate (MBPA), etc. GASP with these initiating systems proceeded to produce corresponding polymers on substrate surfaces. The resulting PMMA had very high PDI values, suggesting an uncontrolled reaction. In an attempt to control the GASP, polymerization with a simple initiating system, Fe(0)/MBPA, was examined on Fe(0)‐metal surfaces, resulting in significant polymerization activity to produce high‐molecular‐weight PMMA. The results of time‐course tests on GASP of MMA and St suggested that a change had taken place to produce physically controlled propagation sites on the Fe(0) powder surfaces.

GASP schemes with a simple initiating system Fe(0)/MBPA.     

Chain Growth Polycondensation as a Polymer Generating Reaction in the Synthesis of Oligo(p‐phenyleneethynylene)s with Low Polydispersity

Summary: The polycondensation of 1‐ethynyl‐2,5‐dihexyl‐4‐iodobenzene in the presence of 1‐ethynyl‐2,5‐dihexyl‐4‐(2‐phenylethynyl)benzene proceeds according to the mechanism of initiated chain growth polycondensation. It has allowed the synthesis of oligomers with a desired molecular weight and a narrow molecular weight distribution. The reasons for the side reaction leading to the formation of diyne compounds are revealed and the presumed mechanism is given. This opens prospects for the preparation of defectless poly(p‐phenyleneethynylene)s with required molecular weights and narrow molecular weight distributions.

     

Gold Nanoparticle/Carbazole Dendron Hybrids

The synthesis, spectral properties, and electropolymerization of hybrid gold nanoparticle core/carbazole dendron shells are reported. Ligand exchange of short‐chain alkane thiol stabilized Au‐NP is compared with direct synthesis using peripheral carbazole dendron ligands. Optical spectra, light scattering, TEM, and electron diffraction data confirm size, polydispersity, and composition. The direct synthesis route yields higher carbazole surface functionality. Higher dendron generation yields larger carbazole species on the surface. The advantage of a larger Au‐NP core is highlighted in terms of conformational mobility and electropolymerizability to form π‐conjugated polycarbazole species. Absorption and fluorescence shift is observed with the electropolymerized film.

     

Characterization of Water‐Dispersible n‐Type Poly(benzimidazobenzophenanthroline) Derivatives

Novel water dispersible poly(benzimidazobenzophenanthroline) polymers functionalized with poly(ethylene oxide) (BBL:PEO) have been investigated by cyclic voltammetry, in situ UV‐vis spectroscopy and atomic force microscopy. The cyclic voltammograms recorded during n‐doping indicate that the drop coated BBL:PEO films retain their properties despite functionalization. A small influence of the PEO side chains on redox properties of the investigated polymers was found, diminishing however after annealing. During spectroscopic experiments structural changes connected with polymer charging were observed (in accordance with a two electron transfer process). The functionalization of BBL with PEO side chains provided an easy processing method to obtain smooth and reproducible polymer films.

     

Macromol. Chem. Phys. 24/2009

The behavior of the transmittance self‐oscillation of a polymer chain with a positively charged MAPTAC group is studied. The polymer concentration exerts considerable influence on the behavior and lifetime of the self‐oscillation. The redox potential and transmittance are measured simultaneously showing that the reactivity of the Ru(bpy)₃ moiety is significantly affected by the polymer aggregation state, originating from the solubility of the polymer chain. The behavior and lifetime of the self‐oscillation can be controlled by changing the design of the polymer structure and concentration.

     

Photoinduced Refractive Index Change of Polymer Films Containing Mesoionic Sulfur‐Substituted Phenyloxatriazolones

We measured photoinduced refractive index changes (see Figure) of polymer films containing various sulfur‐containing mesoionic compounds. PMMA films containing 30 wt.‐% of 3‐phenyl‐1,2,3,4‐thiatriazole‐5‐thione (3PTTT) showed refractive index changes of ?0.036 during photoirradiation, at a wavelength far from the resonant region. An increase in the number of sulfur atoms in the mesoionic compounds doped in PMMA films resulted in the increase in refractive index changes during photoirradiation. The estimation and comparison of the changes in specific refraction and densities of the systems suggest that the change in electronic structure mainly contributes to the refractive index changes of the film in the case of 3PTTT, while the changes in both electronic structure and density equally contribute to the refractive index change in the film with 3‐phenyl‐1,2,3,4‐oxatriazole‐5‐thione (3POTT).

Refractive indices, n, of PMMA films containing various weight fractions of 3POTT (square) and 3PTTT (circle). Open symbols are for n before photoirradiation, filled ones are for n after photoirradiation.     

Anionic Synthesis of Epoxy End‐Capped Polymers

The reaction of living anions of polystyrene (PS) or poly(methyl methacrylate) (PMMA) with epibromohydrin for the synthesis of well‐defined epoxy end‐functionalized polymers is reported. Polyanions were reacted with an excess of epibromohydrin in tetrahydrofuran (THF) at ?78 °C. The functionalities of the resulting polymers were analyzed by matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS), NMR, and size exclusion chromatography (SEC). The epoxy end groups were reacted with 1,1‐diphenyl‐ hexyllithium, and MALDI‐TOF MS and NMR before and after this chemical modification were used to determine the presence of the epoxy end groups. The presence of the epoxy end group was confirmed by anionically polymerizing ethylene oxide from these epoxy end group. The formation of a block copolymer due to the epoxy end groups was proved by SEC analysis. The combined MALDI‐TOF MS, ¹H NMR, and SEC results indicate that epoxy end‐capped PS was obtained in quantitative yield. The method was extended to the synthesis of epoxy end‐capped PMMA. With this polymer the extent of end‐functionalization was high but not quantitative, with non‐dimeric byproducts detected by MALDI‐TOF MS.

     

Photo‐Crosslinked Side‐Chain Liquid‐Crystalline Elastomers for Microsystems

Photo‐crosslinkable side‐chain liquid‐crystalline polymers (LCPs) containing photoreactive benzophenone cores are synthesized in order to obtain their corresponding side‐chain liquid‐crystalline elastomers (LCEs). This strategic synthesis allows thin elastomeric films and their integration into microsystems for actuators and micromachines to be obtained. As an example of this principle, a gripper was developed. The position of its arms can be changed by applying voltages from 1.5 to 3.5 V at different rates. Small changes in the liquid‐crystalline elastomer film cause strains of up to 150% in the microdevice and the capacity to move up to 400 times its own mass due to the nematic‐to‐isotropic transformation.

     

Poly(acrylic acid): A Combined Analysis with Field‐Flow Fractionation and SAXS

Polyelectrolytes such as PAA and its salts are widely used, but are notoriously difficult to characterize due to their polyelectrolyte properties and broad molecular mass distributions. In this paper, we report on a new PAA analysis by combining asymmetrical flow field‐flow fractionation and an advanced SAXS technique using an acoustic levitator to minimize background scattering. The proof‐of‐principle is demonstrated with a mixture of three standard PAAs with different molecular masses. Detailed information on the PAA fractions is available on radii of gyration, polymer contour lengths, and coil conformation. Our method is expected to be applicable for a wide range of water‐soluble synthetic and natural polymers and ideal for molecular masses of 5 × 10³–2 × 10⁵ g · mol^?1.