Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

Polymerization kinetics for the preparation of poly(p-divinylbenzene) via a miniemulsion polymerization process

The polymerization kinetics for the preparation of poly(p-divinylbenzene (p-DVB)) via a miniemulsion polymerization process was studied by the gravimetric analysis and the transmission electron microscopy (TEM) analysis. The influence of the variation of both initiator concentration and polymerization temperature on the polymerization rate was investigated and also the activation energy of p-divinylbenzene was estimated. The evolution of polymer particles was observed by the electronmicrographs and the relatively large size of polymer particles without the formation of coagulum was obtained in the miniemulsion polymerization process.     

Competitive electrochemical oxidation of p-chlorophenol and p-nitrophenol on Bi-doped PbO2

The initial stages of oxidation of aqueous solutions of p-chlorophenol (pcp) and p-nitrophenol (pnp) on Bi-doped PbO₂ electrodes have been studied. From deconvolution and analysis of UV-Vis spectra of the solutions obtained during electrochemical oxidation, benzoquinone and aliphatic acids were identified as the primary oxidation intermediates; oxidation of benzoquinone was found to be the slow step during the early stages of the electrochemical combustion process. The effect of competing adsorption of pcp and pnp on Bi-PbO₂ was also examined, and the presence of pnp in solution was found to inhibit the rate of oxidation of pcp during concurrent oxidation of both phenols.     

Solution properties and kinetics of aggregation of an alkyl-substituted poly(p-phenylene)

Freshly prepared solutions of poly(2,5-di-n-dodecyl-1,4-phenylene) (PPP 12) in toluene are metastable at room temperature with regard to a process which leads to the formation of aggregates composed of up to 100 individual macromolecules. This aggregation process has an induction period of more than 10 h at room temperature. The kinetics of aggregation was investigated by making use of a fast capillary membrane osmometer. Aggregation follows an Avrami-Evans type formalism and suggests that clusters of a lyotropic liquid crystalline phase of the polymer are formed of the same type as observed in the melt. The long induction period of aggregate formation in dilute solution in toluene allows to apply conventional techniques of molar mass determination like membrane osmometry and size-exclusion chromatography (SEC). A relationship [η] = 1.94 × 10⁻³ M^0.94 was found for PPP 12 in toluene at 20 °C and a persistence length of 15.6 nm was derived applying the Bohdanecky-formalism. This gives evidence of the worm-like nature of the non-aggregated PPP 12 in dilute solution.     

Study of the oxidation of solutions of p-chlorophenol and p-nitrophenol on Bi-doped PbO2 electrodes by UV-Vis and FTIR in situ spectroscopy

The oxidation of p-chlorophenol (pcp) and p-nitrophenol (pnp) was studied at Bi-doped PbO₂ (Bi-PbO₂) electrodes. The mass balance between solution composition and flowing charge was obtained from deconvolution of UV-Vis spectra recorded during electrolysis at constant potential. It is shown that the time-dependent production of CO₂ is different for the oxidation of pcp and pnp, indicating different reaction mechanisms for the oxidation of each of these compounds. The reaction kinetics was also followed under thin layer conditions by SNIFTIRS; the similarly increasing signals associated to the generation of CO₂ obtained during oxidation of both compounds indicates that under conditions of restricted mass transfer the mineralization rates of pcp and pnp are similar. The results show that benzoquinone (bq) formed from oxidation of phenols desorbs prior to further oxidation to yield maleic acid (ma), in turn oxidizing further to CO₂.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Acylation of p-xylene over zeolites

Zeolites differing in structure and acidity were tested in liquid phase acylation of p-xylene. Hexanoyl chloride, propionic anhydride and isobutyric anhydride were used as acylating agents. The highest conversions of acylating agent were achieved over large pore zeolites USY (66.3%) and Beta (58.2%). It was found that acylation of p-xylene proceeds only over large pore zeolites Beta and USY. Selectivities to monoacylated p-xylene obtained over USY zeolite decreased in the order: propionic anhydride 78.0% > hexanoyl chloride 67.2% > isobutyric anhydride 33.1%. Diacylated product was formed over zeolite USY with all acylating agents tested but only with hexanoyl chloride over zeolite Beta. It was found that the optimum Si/Al ratio of zeolite Beta for p-xylene acylation with propionic anhydride is 25, while for isobutyric anhydride is 19. Conversion of isobutyric anhydride decreased with increasing isobutyric anhydride concentration and increased with increasing amount of catalyst.     

Fabrication of tridoped p-ZnO thin film and homojunction by RF magnetron sputtering

Tridoping (Al–As–N) into ZnO has been proposed to realize low resistive and stable p-ZnO thin film for the fabrication of ZnO homojunction by RF magnetron sputtering. The tridoped films have been grown by sputtering the AlN mixed ZnO ceramic targets (0, 0.5, 1 and 2 mol%) on GaAs substrate at 450 °C. Here, Al and N from the target, and As from the GaAs substrate (back diffusion) takes part into tridoping. The grown films have been characterized by Hall measurement, X-ray diffraction, photoluminescence, time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. It has been found that all the films showed p-conductivity except for 2 mol% AlN doped film. The obtained resistivity (8.6×10⁻² Ω cm) and hole concentration (4.7×10²⁰ cm⁻³) for the best tridoped film (1 mol% AlN) is much better than that of monodoped and codoped ZnO films. It has been predicted that [(As_Zn−2V_Zn)+N_O] acceptor complex is responsible for the p-conduction. The homojunction fabricated using the best tridoped ZnO film showed typical rectifying characteristics of a diode. The junction parameters have been determined for the fabricated homojunction by Norde's and Cheung's method.     

Novelties of kinetics and mechanism of liquid-liquid phase transfer catalysed reduction of p-nitroanisole to p-anisidine

Anisidines, which are valuable intermediates in dyestuff industry, are synthesised from nitroanisoles. The reduction of nitroanisoles and other substituted nitroaromatics to the corresponding amines can be affected by aqueous inorganic sulphides and polysulphides and the rates of these biphasic reductions are amenable to intensification under phase transfer catalysis (PTC). The selectivity in the reduction of substituted nitroaromatics is greatly affected by the type and number of phases involved in the PTC process. The kinetics and mechanisms of complex L-L PTC processes are not properly understood. This paper delineates novelties of the kinetics and mechanism of L-L PTC reduction of the model compound p-nitroanisole to p-anisidine wherein the sulphide ions get transformed into bisulphide in the aqueous phase and are extracted as ion pairs in the organic phase. A series of reactions of the bisulphide occur to reduce the nitroaromatic to the corresponding amino compound and the Q⁺HSO₃⁻ ion pair is transferred across the interface to react with S²⁻ leading to the formation of the Q⁺SH⁻ ion pair and S₂O₃²⁻. The effects of different parameters are studied to establish this mechanism. The selectivity to the product is 100%.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.     

Direct fluorination of various poly(p-phenylene): Effects of the polymer synthesis and thermal post-treatment

In order to complete a preliminary work about the direct fluorination of poly(p-phenylene) (PPP), the main parameters of the process were investigated. The molecular (chain length and crystallinity) and morphological effects (B.E.T. surface, granulometry) were studied. So, two new starting samples were studied in addition to PPP synthesized by the Kovacic's method (i) a commercial PPP (Polysciences) and (ii) a pyrolyzed PPP, which is similar to an amorphous hydrogenated carbon. Moreover, an annealed PPP (Kovacic's synthesis and post-treatment at 400 °C for 36 h) was compared to the as-synthesized polymer. The reactions with F₂ gas differ significantly in accordance with the synthesis way and the post-treatment (annealing or pyrolysis). Investigations about the direct fluorination of PPPs were carried out for a better understanding of their behavior with respect to molecular fluorine. An extensive characterization was performed by complementary techniques (¹⁹F and ¹³C NMR, FT-IR, and EPR). The fluorine content in the fluorinated PPPs is evaluated by these methods and a reaction mechanism is proposed.     

Packing mode and conformational transition of alkyl side chains in N-alkylated poly(p-benzamide) comb-like polymer

A series of rigid-rod poly(p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA(n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl (n=10) to octadecyl (n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA(n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA(n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all-trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.     

Considerations of polymerization method and molecular weight for proton-conducting poly(p-phenylene) derivatives

Ni(0)-catalyzed coupling polymerization of 2,5-dichloro-4′-phenoxybenzophenone was investigated by varying the ligand and coligand, temperature, reaction time, and solvent. The weight-average molecular weight (M_w) of poly(4-phenoxybenzoyl-1,4-phenylene)s (PPBPs) could be controlled by the polymerization conditions and reached a maximum of 4.4 × 10⁵ g mol⁻¹. Sulfonated PPBPs (S-PPBPs) with various M_ws were prepared with sulfuric acid to study the effect of molecular weight on the chemical and electrical properties of PPBP-based electrolytes. The strong molecular interactions in S-PPBP provided an ion exchange capacity of 2.9 meq g⁻¹ without loss of high mechanical properties. High molecular weight S-PPBPs had more desirable properties for fuel cell applications. While the swelling ratios and hydration numbers of S-PPBPs decreased with increasing molecular weight, the mechanical strength, proton conductivity, and fuel cell performance increased. S-PPBP also showed anisotropic behavior in the swelling and proton conductivity; such behavior is caused by the rigid-rod nature and the liquid-crystal structure.     

Optical and electrical properties of p-type Ag-doped ZnO nanostructures

Zn_1−xAg_xO nanoparticles (NPs) (x=0, 0.02, 0.04, and 0.06) were synthesized by a sol–gel method. The synthesized undoped ZnO and Zn_1−xAg_xO-NPs were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV–visible spectroscopy. The XRD patterns indicated that undoped and Ag-doped ZnO crystallize in a hexagonal wurtzite structure. The TEM images showed ZnO NPs with nearly spherical shapes, with particle size distributed over the nanometer range. Evidence of dopant incorporation is demonstrated in the XPS measurements of the Ag-doped ZnO NPs. The Raman measurements indicated that the undoped and Ag-doped ZnO-NPs had a high crystalline quality. From the result of UV–vis, the band-gap values of prepared undoped and Ag-doped ZnO were found to decrease with an increase in Ag concentration. The obtained undoped and Ag-doped ZnO nanoparticles were used as a source material to grow undoped and Ag-doped ZnO nanowires on n-type Si substrates, using a thermal evaporation set-up. Two probe method results indicated that the Ag-doped ZnO nanowires exhibit p-type properties.     

Preparation and characterization of three-dimensionally ordered macroporous syndiotactic poly(p-methylstyrene)

Three-dimensionally ordered macroporous(3DOM) syndiotactic poly(p-methylstyrene) (sPPMS) with pore size 170 nm was fabricated by means of silica templates using (dbm)₂Ti(OPh)₂/MAO catalytic system. The resulting polymers were characterized by SEM, ¹³C NMR, DSC and GPC. The results indicated that the 3DOM sPPMS were highly syndiotactic. GPC curves showed that the 3DOM sPPMS possessed lower Mn and broader MWD compared with bulk one. Meanwhile, DSC results revealed that three 3DOM sPPMS exhibited crystalline form II, and bulk sPPMS form III.     

Prediction of the electrochemical oligomerization of p-tert-butyl anisole by analyses of the electrolysed solution

The objective of this paper is the study of the electrochemical oxidation of p-tert-butyl anisole in acetonitrile solution and its subsequent electrodeposition on platinum anode. In dry medium, potentiostatic deposition at potential more anodic than these of the two first overlapped waves, which requires relatively high initial substrate concentration, provided an electroactive film. It is shown that whilst the formation of coated electrode at relatively low concentration is difficult in dry medium, it became possible in the presence of an excess amount of water. In the voltammetric study, we observe that the addition of water to the monomer, in the same concentrations leads to the appearance of several new consecutive redox systems, at potential region more anodic than the two overlapped waves. The number of these processes, which are attributed to oxidation of the products of the two first steps, is found to be increased with the water concentration. Combining cyclic voltammetry along with high performance liquid chromatography (HPLC), the effect of the analytical concentration of the monomer and this of the addition of water, on macroscale electrolyses is discussed. Possible reaction mechanisms as well as probable structures for oligomeric products are proposed.     

Synthesis, electroluminescence, and photovoltaic properties of dendronized poly(p-phenylene vinylene) derivatives

Two dendronized poly(p-phenylene vinylene) (PPV) derivatives, ED-PPV and BB-PPV, have been successfully synthesized according to the Gilch route. The obtained polymers possess excellent solubility in common solvents, good thermal stability with 5% weight loss temperature of more than 340 °C. The weight-average molecular weight (M_w) and polydispersity index (PDI) of ED-PPV and BB-PPV are in the range of (1.26-2.34)×10⁵ and 1.37-1.45, respectively. Polymer light-emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/polymer/Ca/Al devices were fabricated, and the PLEDs emitted green-yellow light. The turn-on voltages of the PLEDs based on ED-PPV and BB-PPV were approximately 4.3, and 4.5 V, respectively. The PLED devices of ED-PPV exhibited the maximum luminance of about 157 cd/m² at 10.5 V. Photovoltaic cells with the configuration of ITO/PEDOT:PSS/polymer:C₆₀ (1:1)/Al were also fabricated, and the energy conversion efficiency of the devices based on ED-PPV and BB-PPV was measured to be 0.58, and 0.014%, respectively, under the white light at 75 mW/cm².     

Electrochemical regeneration of activated carbon loaded with p-nitrophenol in a fluidized electrochemical reactor

This paper described a novel electrochemical process for the regeneration of activated carbon (AC) loaded with p-nitrophenol (PNP), aiming to reduce regeneration time and improve cost-effectiveness of the process by adoption of a novel non-active anode of modified lead dioxide and operation of AC in a fluidized mode. The regeneration parameters such as current density, liquid flow rate, NaCl concentration, pH of the solution and regeneration time were systematically investigated. Under the optimum conditions, the regeneration efficiency of AC could reach 90% in 1.5 h, and no significant declination was observed after five-times continuous adsorption-regeneration cycles, confirming the reuse feasibility of the regenerated AC. The adsorption of organic pollutants was confirmed occurring in the micropore of AC, and AC regeneration was mainly due to the decomposition of organics by the attack of active species such as hydroxyl radical that were generated by electrochemical oxidation. The time-space production for AC regeneration has been greatly improved in the present modified process, indicating this regeneration process is much more potentially cost-effective for application.     

Cationic phenyl-substituted poly(p-phenylenevinylene) related copolymers with efficient photoluminescence and synthetically tunable emissive colors

A series of amino-functionalized phenyl-substituted poly(p-phenylenevinylene) (PPV) related copolymers were synthesized by Wittig reaction. Their corresponding cationic conjugated polymers were successfully obtained via a post-polymerization approach. On the basis of FT-IR and ¹H NMR spectra, it was found that phenyl-substituted PPV related copolymers containing alkoxylated benzene (neutral polymer P1 and quaternized polymer P1′), phenylated benzene (neutral polymer P2 and quaternized polymer P2′) and fluorene (neutral polymer P3 and quaternized polymer P3′) moieties are of 55, 80, and 45% cis-vinylic linkage respectively while the polymer containing thiophene moiety (neutral polymer P4 and quaternized polymer P4′) is primarily of trans-vinylic linkage. Their photoluminescence (PL) were conveniently tuned from blue color to yellow color by introducing units with different optoelectronic properties into the PPV backbones. The polymer with fluorene unit and bulky phenylene-substituted benzene unit in the backbone exhibited the highest PL efficiency among these neutral and quaternized PPVs. P4′ containing little cis-vinylic linkage showed complete quenching while P1′-P3′ containing much more cis-vinylic linkage showed incomplete quenching, indicating that the quenching behavior of these cationic PPVs may be highly influenced by the content of cis-vinylic linkage in the PPV backbones.     

Complex voltammetric and fractal study of adsorbed layer’s structure of pure Triton-X-100 and in mixture with o- or p-nitrophenol

Adsorption of well-known surfactant Triton-X-100 (T-X-100) and mixed systems comprising T-X-100 with o- or p-nitrophenols, at the mercury/electrolyte solution interface versus T-X-100 bulk concentration has been studied. Diversified approach comprising capacitive current measurements, desorption peak height analysis, fractal analysis, nonthermodynamic calculation of coefficient of lateral interaction, calculation of relative coverage assuming flat and perpendicular dispositions of molecules, fit with Flory-Huggins isotherms corresponding to different molecular orientations, and predictions of random sequential adsorption (RSA) and equilibrium (generalized RSA) theories, together with analysis of reduction mechanisms of nitrophenols has been used.It is found that the adsorbed layer of T-X-100 and mixed layers are fractal. Fine structural changes of adsorbed layer(s) are identified and related to corresponding changes in fractal dimension. Evidence derived from alternating current (ac) and square wave (sw) voltammetric measurements and theoretical considerations support these conclusions. For the adsorption of T-X-100 four different adsorption phases, corresponding to increasing bulk concentration, are identified and characterized. Mixed systems undergo different changes in microstructure that are reflected in observed changes of reduction mechanisms of nitrophenols. Those are in turn related to the differences in molecular interactions between T-X-100 and certain nitrophenol. The results are relevant for study of any system exhibiting fractal features and accessible to electrochemical methods such as adsorbed films, models of biological membranes, etc.