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Wu Y.-B.,Beijing Institute of Petrochemical Technology | Wu Y.-B.,Beijing Key Laboratory of Special Elastomer Composite Materials | Mao J.,Petrochina | Guo W.-L.,Beijing Institute of Petrochemical Technology | And 6 more authors.
Acta Polymerica Sinica

The styrene cationic polymerization with the CumOH/BF3 initiating system in presence of water was studied. The effects of concentrations of CumOH and water on monomer conversion, polymerization rate and molecular weight of polystyrene were also investigated. An exhaustive mechanistic study of the styrene cationic polymerization in presence of water was proposed by molecular simulation and analyzing terminal structure. It is found that cationic polymerization of styrene exhibits controlled characteristic when [H2O] ≤ 0. 11 mol/L; the content of water in solvent has no significant influence on rate of polymerization reaction,the conversion of monomer and molecular weight. However, cationic polymerization cannot be processed under a high excess of water ([H2O] > 0.11 mol/L). On the basis of calculation results of activation energy,CumOH/BF3 initiating reaction is easier to proceed comparing with CumOH/H2O initiating reaction,which is found to be in line with the experimental results. The initiation reaction of CumOH/BF3 proceeds via activation of C-O bond of ComOH to give active spieces. The water may serve here as a reversible chain transfer agent not only providing control over the polymerization reaction,but also forming hydroxy terminal groups. Source

Feng W.,Beijing Institute of Petrochemical Technology | Feng W.,Beijing Key Laboratory of Special Elastomer Composite Materials | Zhou H.,Beijing Institute of Petrochemical Technology | Zhou H.,Beijing Key Laboratory of Special Elastomer Composite Materials | And 2 more authors.

Nanocrystalline lead selenide (PbSe) thin films with varied thickness were deposited on glass substrates by thermal evaporation technique. Physical and surface properties of PbSe films were examined by XRD, AFM, UV-Vis spectra. It was found that the structural and optical properties of the PbSe films were strongly dependent on thickness. On one hand, the particles were uniformly distributed in the surface for the thinner samples. On the other hand, however, the particles began to aggregate and worm-like structures appeared for the thicker ones (93 nm and 127 nm). The absorption band-edge was red shifted with increasing thickness. The optical band gap ranging 2.04-2.30 eV with thickness was observed. This could be attributed to the increasing of grain size and the improvement of film uniformity. © 2015 Elsevier Ltd. Source

Feng W.,Beijing Institute of Petrochemical Technology | Feng W.,Beijing Key Laboratory of Special Elastomer Composite Materials | Wang X.,Beijing University of Chemical Technology | Chen F.,Beijing Institute of Petrochemical Technology | And 8 more authors.
Thin Solid Films

PbSe films were prepared by radio frequency magnetron sputtering from PbSe slices target under different substrate temperatures (from room temperature to 300 °C). The effect of substrate temperature on structural properties of PbSe thin film was investigated. The surface morphology and the crystal structure of film were determined using field emission scanning electron microscopy and X-ray diffractometry, respectively. It was found that the grain shape changed with substrate temperature. When the substrate temperature was below 250 °C, most of the crystal grains were spherical in shape. For temperatures above 250 °C, the grains transformed to triangle or prismatic ones. Meanwhile, with increasing substrate temperature, the preferential orientation of the film changed from (200) to (220). To figure out the intrinsic mechanisms for this behavior, the texture coefficient, as well as the comparison between surface energy and elastic strain energy was performed. At lower temperature, the film growth was determined by surface energy, which was replaced by strain energy at higher temperature. Therefore, the diversity of crystal structure and morphology of the films at different substrate temperatures occurred. Moreover, the electrical properties of the p-type PbSe films are also quite dependent on substrate temperature. With substrate temperature increased, the electrical resistivity decreased from 1.88 to 0.14 Ω cm, while the carrier concentration increased from 1.74 × 1018 to 4.08 × 1019 cm- 3 as the mobility was enhanced from 0.54 to 2.21 cm2/Vs. © 2015 Elsevier B.V. All rights reserved. Source

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