Zhongrong Shen

Spatial and temporal variability of trace metals in aerosol from the desert region of China and the Yellow Sea

[i] From spring to early summer of 1995 and 1996, about 180-190 aerosol samples were collected from three observatories at Northwest China desert region (i.e., Minqin), coastal suburb area (i.e., Qingdao), and an island in the Yellow Sea (i.e., Qianliyan), respectively. The samples were analyzed to determine the concentrations of trace metals (Al, Fe, Mn, Na, Cr, Zn, Cu, Co, Ni, Pb, V, Sr, and Cd). Data are examined to understand the distribution of trace metals in aerosols at an upwind desert region and downwind marine recipient under westerly flow. The result shows that trace metal composition of aerosols vary considerably in time and space. Trace metal levels display a drastic seasonal change at both Qingdao and Qianliyan, with concentrations generally 2-3 times higher in spring than summer. Daily variation of trace metal concentrations at Minqin is more significant than Qingdao and Qianliyan, however. The enrichment factors for the crustal source (EF crust ) at Minqin are relatively low and unimportant compared with those at Qingdao and Qianliyan. Some of the trace species like Pb, Zn, and Cd have relatively high contributions from the anthropogenic source (Rp), and >98% are found at Qingdao and Qianliyan, with EF crust values 1-2 orders of magnitude higher than Minqin. Manganese is mainly from low-temperature weathering products and the contribution from crustal source (R c ) is >70% at Qingdao and Qianliyan. The coastal atmosphere responds to the episodic dust storms in the desert region (i.e., Minqin) by an increase in aerosol level and a higher concentration of crust-dominated materials. The percentage contributions from the crustal source (Rc) of trace metals, such as Pb, Cd, and Zn, could be increased considerably by 5 - 10 folds higher during the passage of cold fronts than during calm weather period over the Yellow Sea.

Study of the Steric Tacticity of Novel Soluble Ladderlike Poly(phenylsilsesquioxane) Prepared by Stepwise Coupling Polymerization

A novel kind of soluble ladderlike poly(phenylsilsesquioxane) (LPPS) was prepared by stepwise coupling polymerization. Various techniques, such as fluorescence spectroscopy, X-ray diffraction (XRD), molecular simulation and calculation, were combined to indicate that the steric structure in LPPS was predominantly cis-isotactic. It is anticipated that stepwise coupling polymerization is a useful synthetic method for preparing ladder-like poly(silsesquioxane)s with cis-isotactic structure, which have potential applications as functional polymers or as precursors for the further synthesis of novel advanced polymers. Schematic presentation of the steric strocture of LPPS: (a) cis-isotactic (b) cis-syndiotactic.

A triphenylene-containing side chain liquid crystalline ladder-like polysiloxane and its highly ordered superstructure

A liquid crystalline discotic triphenylene-containing side chain ladder-like polysiloxane (LPS) derivative was prepared by hydrosilylation. The superstructure was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and isotherm surface pressure (π)-area (A) diagrams based on LB-film experiments. The XRD results suggest that the discotic triphenylene units in the side chains stack to form a columnar structure and the columns further align with each other to form a board-like superstructure because of the semi-rigidity of the ladder-like backbone. This suggestion has been confirmed by parallel nanowire-like stripes observed in the AFM image. Mixing small amounts of the corresponding low molar mass molecules with the polymer leads to a more ordered and denser columnar stacking, as shown by sharpened XRD patterns and a π-A curve with a steeper slope, higher collapse pressure and lower collapse area than those obtained either for the low molar mass molecules or the polymer individually.

Synthesis and Characterization of Novel Alcohol-Soluble Ladderlike Poly(silsesquioxane)s Containing Side-Chain Hydroxy Groups

Two novel kinds of alcohol-soluble ladder-like poly(silsesquioxane)s containing side-chain hydroxy groups (OH-T 1 and OH-T 2 ) were prepared successfully for the first time by hydrolysis of ladderlike poly(silses-quioxane)s with side-chain ester groups (Ester-T 1 and Ester-T 2 ), which were synthesized by stepwise coupling polymerization. A variety of characterization methods including FT-IR, 1 H NMR, 13 C NMR, 29 Si NMR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vapor pressure osmometry (VPO), gel permeation chromatography (GPC), and X-ray diffraction (XRD) were combined to demonstrate that the obtained alcohol-soluble polymers have ladderlike structures, although some structural defects still existed.

Synthesis and mesomorphic properties of novel fishbone-like liquid crystalline polysilsesquioxanes VI. Fishbone-like, ester-based liquid crystalline polysilsesquioxanes

Two novel kinds of fishbone-like, ester-based, liquid crystalline, random copolysilsesquioxanes, LC1-CH3-P and LC2-CH3-P, have been synthesized for the first time by stepwise coupling polymerization (SCP) from trichlorosilane monomers (RSiCl3) containing mesogenic ester groups, using three main steps including preaminolysis, hydrolysis and polycondensation. Two new monomers 4-(11-trichlorosilylundecloyloxy)phenyl 4-methoxybenzoate (M1) and 4-(3-trichlorosilylpropoxy)phenyl 4-methoxybenzoate (M2) have been synthesized by hydrosilylation reaction of trichlorosilane and the mesogens 4-n-undecenoyloxyphenyl 4-methoxybenzoate and 4-allyloxyphenyl 4-methoxy-benzoate, respectively, in the presence of dicyclopentadienylplatinum(II) chloride (Cp2Ptcl2) catalyst. The structures and mesomorphic properties of LC1-CH3-P and LC2-CH3-P were investigated by FTIR, 1H NMR, 13C NMR, 29Si NMR, gel permeation chromatography, polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. It is proposed from the characterization data that these two polymers not only have an ordered ladder-like, double main chain, but also show thermotropic smectic behaviour with high clearing points and wide mesophase ranges (ΔT), which may hold promise for potential applications as highly stable gas chromatographic stationary phases.

Synthesis and characterization of a metal chelate-bridged quasi-ladder main chain discotic liquid crystal polymer

A metal chelate-bridged quasi-ladder discotic liquid crystal polymer (DLCP) has been prepared by a controlled chelation reaction of cupric ions with β-diketone groups on two adjacent poly(AADK-HMM) chains, synthesized by the hydrosilylation of a bis-allyl groupterminated β-diketone monomer and 1,1,3,3-tetramethylhydrodisiloxane (HMM). X-ray diffraction patterns of the samples annealed in the mesomorphic state or cooled from the isotropic phase demonstrated the existence of an ordered columnar structure on short or long range scales, respectively. The fact that the molecular weight of the cupric complex is approximately twice that of the parent polymer indicates that the quasi-ladder double chain polymer is the predominant product although some terminal defects are present.