Shen Zhiquan

Progress in coordination polymerization by rare earth catalysts

Rare earth catalysts represent an unprecedented case where either butadiene, isoprene or mixtures of butadiene and isoprene can be polymerized to elastomers with high content of cis-isomer and good properties. As high as 98% cis-polyacetylene films with metallic sheen can be prepared by rare earth catalysts at room temperature. Rare earth catalysts are excellent as high cis-stereospecific polymerization catalysts for acetylenes. High molecular weight polyepoxides can also be prepared by rare earth catalysts.

Exploitation of rare earth catalysts in polymer syntheses

The studies over forty years on rare earth catalysts in polymer syntheses of diene, alkyne, alkylene oxide, thiirane, carbon dioxide copolymerization, lactide, caprolactone, cyclic carbonate and so forth in China have been reviewed.

Ring opening polymerization of ethylene oxide by the Y(P204)3―Al(i-Bu)3―H2O catalyst

Abstract Ring opening polymerization of ethylene oxide was carried out for the first time in toluene using the rare earth coordination catalyst: Y(P204)3 AL(i-Bu)3-H2O. The polymerization activity is strongly dependent upon the molar ratio of these three components and polymerization conditions. This new catalyst gives high molecular weight poly(ethylene oxide) with a high reaction rate and a high yield. Poly(ethylene oxide) so prepared was characterized by infrared spectrophotometry, differential scanning calorimetry and X-ray diffraction.

New scandium coordination catalysts for the cis polymerization of acetylene

The catalytic activity of scandium has not been widely studied. This article reports the first study of a new kind of Ziegler-Natta catalyst, the combination of a scandium compound and aluminum trialkyl, for the polymerization of acetylene. Some characteristics and kinetic aspects of acetylene polymerization by scandium catalysts and the results of the characterization of polyacetylene so obtained are described. High cis polyacetylene films (95% cis) with silvery metallic sheen and high crystallinity (70%) were obtained at ambient temperature (30–0 °C). The electrical conductivity of iodine doped polyacetylene reached hundreds ohm−1 cm−1.

Anhydrous lanthanide chlorides doped rare-earth polyacetylene

Abstract Lanthanide chlorides (LnCl 3 ) of all fifteen rare- earth elements, except Pm, have been used as new dopants for the chemical doping of rare-earth polyacetylene (PA) films. The doping reaction takes place in a saturated tetrahydrofuran solution of LnCl 3 . The doped PA films exhibit an increase of 1–3 orders in conductivity as compared with the undoped one and, moreover, can be used as good substrates for the redoping with FeCl 3 or I 2 to prepare films having high and more stable conductivity. Characterizations using techniques of infrared spectrophotometry, electron spin resonance, differential scanning calorimetry and X-ray diffraction have also been performed for the resuttant PA. It is demonstrated by the physical characterizations that the dopant species are partially coordinated to the PA chains but have no significant influence on the PA structure.

Synthesis of high cis polyacetylene with coordination catalysts consisting of rare earth naphtenate

Abstract High cis polyacetylene films with silvery metallic appearance were prepared by coordination catalysts, comprising of naphthenates of all fifteen rare earth elements, and trialkyl aluminum at room temperature. The resultant polyacetylene (PA)was characterized by infrared spectrophotometry, electron spin resonance, X-ray diffraction, scanning and transmission electron micrography, differential scanning calorimetry and electrical resistivity measurements. The enthalpy and apparent activation energy of thermal cis-trans isomerization of 98% cis PA were 1.7–1.8 kcal/mol and 19.0 kcal/mol respectively. Rare earth PA shows higher thermal and antioxidization stability than does PA with other catalysts.

Detection of free surface composition and molecular-level structural development of styrene(S)/butadiene(B) block copolymer films during a solution-to-film process

The surface chemical structure development in solution-cast styrene(S)/butadiene(B) block copolymer films as a function of solvent evaporation time was investigated using sum frequency generation vibrational spectroscopy (SFG). The surface structure formation of the styrene(S)/butadien(B) block copolymer (30 wt% PS) films during the solution-to-film process was found to be controlled mainly by dynamic factors, such as the mobility of the PB block in solution. For SB diblock copolymers, a pure PB surface layer was formed only when the film was cast by dilute toluene solution. With increasing concentration of casting solution, PB and PS components were found to coexist on the film surface, and the morphology of the PB component on the film surface changed from cylindrical rods to spheres. For SBS triblock copolymers, a small amount of PS component existed on the surface even if the film was cast by 1.0 wt% toluene solution. In addition, PS components at the outermost layer of the film increased and the length of PB cylindrical rods on the surface decreased with increasing concentration of casting solution.

Copolymerization of Propylene Oxide and CO 2 Catalyzed by a Rare Earth Borohydride-Diethylzinc-Glycerine Ternary System: Copolymerization of Propylene Oxide and CO 2 Catalyzed by a Rare Earth Borohydride-Diethylzinc-Glycerine Ternary System

A ternary catalytic system composed of rare earth borohydrides, diethylzinc, and glycerine has been developed and found to be effective for the copolymerization of propylene oxide (PO) with carbon dioxide. The effect of catalyst composition and reaction conditions on the copolymerization was examined through orthogonal experiments. With Y(BH4)(3)center dot 3THF-ZnEt2-glycerine molar ratio of 3:60:20, the highest turnover frequency (TOF) of 4 908 g/(mol.h) was achieved at 80 degrees C and 3.0 MPa of CO2 using 1,2-dimethoxyethane as solvent. The poly(propylene carbonate) had a carbonate unit content of 95.7% and number-average molecular mass of 6.97 x 10(4).

Environmental adaptivity of the surface of styrene-isoprene-styrene tri-block copolymers films controlled by the film-preparation kinetics

The responses of the surface structures to the solvent vapor treatment for the films of styrene(S)/ isoprene(I)/styrene(S) tri-block copolymers (SIS) prepared by various casting solvents and film-formation methods (solvent-casting and spin-coating) were investigated by contact angle measurement, atomic force microscopy (AFM) and sum frequency generation vibrational spectroscopy (SFG). It was shown that the surface wettability of the SIS solvent-cast films (cyclohexanone as solvent) and spin-coated films (toluene as solvent) exhibited the reversibly switching properties, if alternately exposed them to the vapor of PI-selective (cyclohexane) and PS-selective (butanone) solvents. However, for the solvent-cast films prepared by cyclohexane and toluene solution, the wettability of the films surface did not change, regardless of which solvent was applied in vapor treatment. It was claimed that the difference in the phase-separation structure of the SIS films prepared using different casting solvents and film-formation methods is the main reason for the discrepancy in the surface adaptive behavior. If the films have the equilibrium phase structures, the energy barrier for the conformation adjustment is apparently larger, and therefore it is hard to change the aggregation structure to accommodate the new solvent-vapor environment. While for the films having the non-equilibrium phase-separation structures, the conformational adjustment under the different solvent vapor will become relatively easier. Owing to this effect, the prepared SIS films with various film-formations kinetics can form different aggregation structures after a specific solvent vapor treatment, and finally leads to dissimilar surface structure. As a result, the surface wettability of these films exhibit different responsiveness to solvent vapor.

Effects of substrate/polymer interfacial interactions on dynamics of thin polystyrene films

The glass transition temperature ( T g) and viscoelasticity of thin polystyrene (PS) films supported on Si/Si-H and Si/SiO2 substrates were investigated using an ellipsometry and force-distance (F-D) measurements of atom force microscopy. It was found that T g of thin PS films deposited on either Si/Si-H or Si/SiO2 decrease with decreasing of film thickness. However, T g of PS film on Si/SiO2 substrate depressed more dramatically than that on Si/Si-H. The threshold thickness for T g reduction of thin PS film on Si/SiO2 (110 nm) is higher than that of film on Si/Si-H (40 nm). Meanwhile, thin PS film supported by Si/SiO2 exhibits the higher thermal expansivity compared with that on Si/Si-H substrate. Surface F-D measurements reveal the film on Si/Si-H substrate is stiffened, showing a higher elastic modulus. In order to understand the mechanism of the substrate effect, the interfacial energy and long-range van der Waals potential ( Φ vdw ) were investigated and a strong attractive interaction between PS and Si/Si-H substrate was found. Thus, the packing density was enhanced and the molecular mobility of PS chains at Si/Si-H/PS interface was suppressed. This strong interaction resulted in higher T g and elastic modulus of thin PS film compared with that on Si/SiO2 substrate.