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     

Synthesis,characterization, and electrical properties of polypyrrole/multiwalled carbon nanotube composites

Size‐controllable polypyrrole (PPy)/multiwalled carbon nanotube (MWCNT) composites have been synthesized by in situ chemical oxidation polymerization directed by various concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB). Raman spectra, FTIR, SEM, and TEM were used to characterize their structure and morphology. These results showed that the composites are core (MWCNT)–shell (PPy) tubular structures with the thickness of the PPy layer in the range of 20–40 nm, depending on the concentration of CTAB. Raman and FTIR spectra of the composites are almost identical to those of PPy alone. The electrical conductivities of these composites are 1–2 orders of magnitude higher than those of PPy without MWCNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6449–6457, 2006     

Poly(ortho‐phenylene ethynylene)s: Synthetic accessibility and optical properties

Poly(ortho‐phenylene ethynylene)s (PoPEs) have been synthesized via an in situ activation/coupling AB′ polycondensation protocol. The resulting polymers have been characterized by several analytical methods and are shown to have no structural defects. Although the Sonogashira–Hagihara polycondensation reaction is less efficient than for the preparation of the corresponding meta‐ and para‐linked polymers, presumably because of steric hindrance caused by the ortho substituents, the process can be accelerated by the use of microwave irradiation. Optical spectroscopy indicates solvent‐dependent conformational changes between extended transoid and helical cisoid conformations, providing the first experimental evidence for solvophobically driven folding of the PoPE backbone. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1619–1627, 2006     

Single electron transfer–degenerative chain transfer living radical polymerization of N‐butyl acrylate catalyzed by Na2S2O4 in water media

Living radical polymerization of n‐butyl acrylate was achieved by single electron transfer/degenerative‐chain transfer mediated living radical polymerization in water catalyzed by sodium dithionate. The plots of number–average molecular weight versus conversion and ln[M]₀/[M] versus time are linear, indicating a controlled polymerization. This methodology leads to the preparation of α,ω‐di(iodo) poly (butyl acrylate) (α,ω‐di(iodo)PBA) macroinitiators. The influence of polymerization degree ([monomer]/[initiator]), amount of catalyst, concentration of suspending agents and temperature were studied. The molecular weight distributions were determined using a combination of three detectors (TriSEC): right‐angle light scattering (RALLS), a differential viscometer (DV), and refractive index (RI). The methodology studied in this work represents a possible route to prepare well‐tailored macromolecules made of butyl acrylate in an environmental friendly reaction medium. Moreover, such materials can be subsequently functionalized leading to the formation of different block copolymers of composition ABA. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2809–2825, 2006     

电子探针定量分析的标准样品——几种多元氧化物单晶

在很高的温度和适宜的生长条件下,分别采用熔盐籽晶法和高温引上法生长了高质量的YAP、NAB、KTP、LN、BBO、SBN等多元氧化物单晶,它们具有优良的物理化学性能,严格的化学比,固定的组成与结构以及较好的化学均匀性和电子束轰击下的稳定性。广泛地用于激光和非线性光学领域。我们选用这些晶体为原材料研制电子探针定量分析的标准样品。经过测量和标定,这些单晶标样符合中华人民共和国国家标准GB 4930-85(电子探针显微分析标准样品通用技术条件)的规定。含有稀土元素的标样如NAB和YAP能发出绿色荧光,是电子显微术中理想的阴极发光材料。     

Ab initio calculations of small hydrides including electron correlation

Five different structures of CH₅ ⁺ and one structure of CH₅ ^– are calculated using a gaussian basis both in the SCF approximation and with the inclusion of electron correlation in the independent electron pair approximation (IEPA). While on SCF level the C _sstructure of CH₅ ⁺ has to lowest energy, the energy difference between the C _sand C _2vstructures becomes negligible if correlation is included. In contrast to this the approach of a proton to CH₄ at large and intermediate distances is most favorable towards a corner of the CH₄ tetrahedron which means a structure. The decomposition of CH₅ ⁺ into CH₃ ⁺ and H₂ requires 20kcal/mol on SCF level and 40 kcal/mol if correlation is included.     

Structure of Charge Transfer Reaction Complexes Formed in Anionic Polymerization of Isoprene

A new mechanism is suggested for the anionic polymerization of isoprene. The key moment of this mechanism is thermal electron excitation of the complex of a living polymer with a monomer to the low lying S₁ (T₁) state involving a charge (electron) and (Li⁺) cation transfer from the terminal unit to the monomer molecule. It is stated that the probability of chemical bonding depends on the spin density on the radical centers of reactant molecules and on the geometry of the reaction complex. The semiempirical AM1 and ab initio 6-31G* quantum-chemical calculations revealed strong interaction for the ground electronic state of the complex (5-10 kcal/mole) and low energies of the excited triplet levels (<10 kcal/mole).     

ELECTRON PARAMAGNETIC RESONANCE STUDIES OF SINGLE CRYSTAL SODIUM HEXAMOLYBDOCHROMATE (Ⅲ)Cr~(3+)/Na_3(AlMo_6O_(24)H_6)·8H_2O

An X-band EPR study on a Na_3(CrMo_6O_(24)H_6)·8H_2O single crystal diluted by its isomor-phic compound Na_3(AlMo_6O_(24)H_6)·8H_2O at room temperature is reported. Using the least squares-fitting method to simulate the EPR data for principal planes, the Hamiltonian parameterswere obtained. The principal values of the g tensors are g_(ZZ) = 1.904, g_(XX)= 1.973, g_(YY)=1.933. The zero field splitting tensor parameters are D = 0.275 cm~(-1), E = 0.05 cm~(-1). The fielddependence of Cr~(3+) energy levels with field at different angles from the principal axes whenthe field is along the principal planes is calculated based on these experimental parameters.The isofrequency plots of calculated field vs. angle are also shown. They agree well with theexperimental results.     

Solid-supported Hantzsch—Biginelli reaction for syntheses of pyrimidine derivatives

The microwave-assisted dry media technology was utilized for the synthesis of some novel derivatives in the Hantzsch—Biginelli reaction. In this eco-friendly approach, the usage of organic solvents and hazardous reagents resulting in corrossion of materials was minimized, giving high yields of products within a short reaction time.