Diffractive vector meson production at HERA: From soft to hard QCD

Experimental results from HERA on diffractive vector meson production and their theoretical interpretation within microscopic QCD are reviewed with an emphasis on the BFKL color dipole and k _T -factorization approaches. The text was submitted by the authors in English.     

Nuclear multifragmentation and phase transitions in hot nuclei

Nuclear multifragmentation is a new, multibody, decay mode of very hot nuclei. The key properties of this process that were measured are considered, such as the space-time and temperature characteristics. The experimental data for the critical temperature of the nuclear liquid-gas-phase transition are analyzed. Thermal multifragmentation is interpreted as a result of spinodal decomposition, which is actually the specific nuclear liquid-fog-phase transition of the first order. The text was submitted by the author in English.     

Synthesis and comparative solution properties of single‐, twin‐, and triple‐tailed associating ionic polymers based on diallylammonium salts

The cycloterpolymerizations of single‐, twin‐, and triple‐tailed hydrophobes with hydrophilic monomer N,N‐diallyl‐N‐carboethoxymethylammonium chloride and sulfur dioxide afforded a series of cationic polyelectrolytes (CPEs) in excellent yields. These CPEs, upon the acidic hydrolysis of the pendent ester groups, gave the corresponding pH‐responsive cationic acid salts, which, upon a treatment with sodium hydroxide, were converted to polybetaines (PBs), anionic polyelectrolytes (APEs), and PB/APE polymers containing various proportions of zwitterionic (PB) and anionic fractions (APE) in the polymer chain. At a shear rate of 0.36 s⁻¹ at 30 °C, salt‐free water solutions of the CPEs (2 g/dL) containing 8, 4, and 2.67 mol % of the single‐, twin‐, and triple‐tailed hydrophobes (all having 8 mol % octyloxy tails) had apparent viscosity values of 70, 2800, and 396,000 cps, respectively. The PB/APE polymer with a ratio of 33:67 for the zwitterionic and anionic fractions in the polymer chain gave the highest viscosity value. The superior viscosity behavior of the polymers containing the triple‐tailed hydrophobe was attributed to the blocky nature of the comonomer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5480–5494, 2006     

Effect of stoichiometry on liquid crystalline supramolecular polymers formed with complementary nucleobase pair interactions

We report herein studies on the liquid crystalline behavior of a series of supramolecular materials that contain different ratios of two complementary symmetrically-substituted alkoxy-bis(phenylethynyl)benzene AA- and BB-type monomers. One monomer has thymine units placed at either end of the rigid mesogenic core, while the other has N⁶-(4-methoxybenzoyl)-adenine units placed on the ends. Differential scanning calorimetric and polarized optical microscopy studies have been carried out on these systems. These studies show that the material's behavior is strongly dependent on its thermal history. As a result, the materials can exhibit, on heating, either a liquid crystalline phase, a crystalline phase, or the coexistence of crystalline and liquid crystalline regions. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5049–5059, 2006     

Lightly crosslinked,mesomorphic networks obtained through the reaction of dimeric,liquid‐crystalline epoxy–imine monomers and heptanedioic acid

We reacted various dimeric, liquid‐crystalline epoxy–imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid‐crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed‐frequency and frequency‐sweep modes in the shear sandwich configuration. The arrangement in the liquid‐crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid‐crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid‐crystalline phase with respect to side‐chain liquid‐crystalline elastomers and that the time–temperature superposition principle did not hold through the liquid‐crystalline‐to‐isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270–6286, 2006     

Differential AC-chip calorimeter for glass transition measurements in ultrathin films

A differential AC-chip calorimeter capable of measuring the step in heat capacity at the glass transition in nanometer-thin films is described. Because of the differential setup, pJ/K sensitivity is achieved. Heat capacity can be measured for sample masses below 1 ng in broad temperature range as needed for the study of the glass transition in nanometer-thin polymeric films. Relative accuracy is sufficient to investigate the changes in heat capacity as the step at the glass transition of polystyrene. The step is about 25% of the total heat capacity of polystyrene. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the frequency range from 1 Hz to 1 kHz. The glass transition in thin polystyrene films (50–4 nm) was determined at well-defined experimental time scales. No thickness dependency of the glass transition temperature was observed within the error limits (±3 K)—neither at constant frequency (40 Hz) nor for the trace in the activation diagram (1 Hz–1 kHz). © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2996–3005, 2006     

Control of the conjugation length and solubility in electroluminescent polymers

A new type of cyclolinear polymer, poly(phenylene vinylene‐alt‐cyclotriphosphazene), was synthesized through Heck‐type coupling reactions to produce π‐conjugated macromolecules with excellent solubility and precise electronic control of the band‐gap energy. This synthesis method is capable of producing well‐defined alternating polymers. The method is highly adaptable and can be readily used for other chromophore systems. The resulting polymers were also capable of accommodating a wide variety of substituents on the cyclophosphazene rings with minimal effect on the electronic properties. The band gap and electron affinities of the polymer were varied through the manipulation of the π‐conjugated unit located between the insulating phosphazene rings. Each chromophore matched the intended conjugation length consistently throughout the macromolecules. The polymers were good film formers because of the chosen substituents on the phosphazene rings. The absorbance of the polymers indicated minimal spectral shift from the monomer absorbance. This suggested an effective insulation of each chromophore unit from its neighbors by the phosphazene rings. Solution photoluminescence efficiencies were found to be up to 44.1%. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 69–76, 2006     

Synthesis and optical properties of a poly(p‐phenylenevinylene) derivative and polyfluorenes with bipolar groups along the main chain

A poly(p‐phenylenevinylene) derivative (PPV–TPA)] and a series of statistical copolyfluorenes (PF–TPA)] containing oxadiazole and triphenylamine segments along the main chain were synthesized by the Heck reaction and nickel‐mediated coupling, respectively. The PF–TPA copolyfluorenes with relatively low contents of oxadiazole and triphenylamine units were readily soluble in common organic solvents, whereas the other copolyfluorenes displayed lower solubility. PPV–TPA showed excellent solubility in solvents such as tetrahydrofuran (THF), dichloromethane, chloroform, and toluene. Thin films of the polymers absorbed light in the range of 375–396 nm and had optical band gaps of 2.76–2.98 eV. They emitted blue‐green light with a maximum at 414–522 nm. The fluorescence quantum yields in THF solutions were 0.08–0.53. The copolyfluorene PF–TPA thin films with high contents of oxadiazole and triphenylamine moieties emitted pure blue light that remained stable even after annealing at 150 °C for 4 h in air. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3556–3566, 2006     

Copolymerization of N‐vinylcaprolactam and glycidyl methacrylate: Reactivity ratio and composition control

Free‐radical copolymerizations of N‐vinylcaprolactam (VCL) and glycidyl methacrylate (GMA) were investigated to synthesize temperature‐responsive reactive copolymers with minimized compositional heterogeneity. The average copolymer composition was determined by Fourier transform infrared and nuclear magnetic resonance techniques. The reactivity ratios for VCL and GMA were found to be 0.0365 ± 0.0009 and 6.44 ± 0.36 by the Fineman–Ross method and 0.039 ± 0.006 and 6.75 ± 0.29 by the Kelen–Tudos method, respectively. When prepared by batch polymerization, VCL–GMA copolymers had a highly heterogeneous composition and fractions of different solubilities in water. The use of a gradual feeding technique, which included the sequential addition of more reactive GMA monomer into the reaction, yielded copolymers with much more homogeneous composition. The produced copolymers with 0.9 and 0.11 fractional GMA contents preserved their temperature‐responsive properties and precipitated from aqueous solutions when the temperature exceeded 31 °C. The GMA units in the VCL–GMA copolymers were capable of reacting with amino end‐functionalized poly(ethylene oxide) at room temperature to produce poly(N‐vinylcaprolactam)–poly(ethylene oxide) graft copolymers. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 183–191, 2006     

Synthesis and characterization of poly(arylene ether)s containing 6‐(4‐hydroxyphenyl)pyridazin‐3(2H)‐one or 6‐(4‐hydroxyphenyl)pyridazine moieties

A series of novel soluble pyridazinone‐ or pyridazine‐containing poly(arylene ether)s were prepared by a polycondensation reaction. The pyridazinone monomer, 6‐(4‐hydroxyphenyl)pyridazin‐3(2H)‐one ( 1 ), was synthesized from the corresponding acetophenone and glyoxylic acid in a simple one‐pot reaction. The pyridazinone monomer was successfully copolymerized with bisphenol A (BPA) or 1,2‐dihydro‐4‐(4‐hydroxyphenyl)phthalazin‐1(2H)‐one (DHPZ) and bis(4‐fluorophenyl)sulfone to form high‐molecular‐weight polymers. The copolymers had inherent viscosities of 0.5–0.9 dL/g. The glass‐transition temperatures (T_g's) of the copolymers synthesized with BPA increased with increasing content of the pyridazinone monomer. The T_g's of the copolymers synthesized from DHPZ with different pyridazinone contents were similar to those of the two homopolymers. The homopolymers showed T_g's from 202 to 291 °C by differential scanning calorimetry. The 5% weight loss temperatures in nitrogen measured by thermogravimetric analysis were in the range of 411–500 °C. 4‐(6‐Chloropyridazin‐3‐yl)phenol ( 2 ) was synthesized from 1 via a simple one‐pot reaction. 2 was copolymerized with 4,4′‐isopropylidenediphenol and bis(4‐fluorophenyl)sulfone to form high‐T_g polymers. The copolymers with less than 80 mol % pyridazinone or chloropyridazine monomers were soluble in chlorinated solvents such as chloroform. The copolymers with higher pyridazinone contents and homopolymers were not soluble in chlorinated solvents but were still soluble in dipolar aprotic solvents such as N‐methylpyrrolidinone. The soluble polymers could be cast into flexible films from solution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3328–3335, 2006