Preparation and Characterization of Homo‐ and Co‐Polymers of Some Vinyl Monomers via ATRP by Using Imine Macrocycle as Ligand

Imine macrocyclic ligand M₁ was involved in homo‐ and co‐polymerization of some vinyl monomers via atom transfer radical polymerization technique (ATRP). Hereby, vinyl acetate, styrene and methyl acrylate monomers were homopolymerized. On the other hand, they were involved in copolymerization with MMA. M₁∶CuBr∶initiator∶monomer percentages were 1∶2∶4∶400. ¹HNMR confirmed the structures of the resulting polymers. The thermal behaviors of some selected polymers were studied.     

Polymerization of 4—Vinylpyridine by Lanthanide Coordination Catalyst

Polyvinylpyridines are an important class of polymers that exhibit interesting properties due to the presence of the nitrogen atom in the pyridine ring. The weakly basic nitrogen atom makes possible a variety of reactions on vinylpyridine polymers, e.g. reaction with acids, quaternization and complexation of metals. In addition, these polymers are mainly attractive in applications as polyelectrolytes, polymeric reagents etc. Few papers about polymerization of 4-vinylpyridine (4-Vpy) with co…     

Study of a Ru-La/Zr02 Catalyst Prepared by Precipitation Method for Selective Hydrogenation of Benzene to Cyclohexene

A Ru-La/ZrO2 catalyst was prepared by the precipitation method, in which Ru was an active component, La was a promoter and ZrO2 was a dispersant. Comparing with the catalyst prepared by the chemical reduction method, the Ru-La/ZrO2 exhibited higher activity and better selectivity. At 140 ℃ and hydrogen pressure of 5 MPa, the C6H10 selectivity reached 70% at a C6H6 conversion of 35% for a reaction time was 5 min and the total La/Ru loading was 10%. Textural parameters of the catalyst were obtained by physical adsorption, BET surface area and specific pore volume measurements. The catalyst sample gave a BET area of 41 m2/g and a specific pore volume of 1.1 cm^3/g, and the most probable pore distribution was located at 5 to 10 nm. H2-TPR measurements showed that ruthenium oxide could be reduced to its metallic state at about 403 K. XRD determinations indicated that ruthenium and lanthanum were highly dispersed on the zirconia. A significant advantage of the Ru-La/ZrO2 catalyst is that it can be used directly in its unreduced state for the selective hydrogenation of benzene.     

Studies on the Cationic Copolymerization of α-Pinene and Styrene with Complex SbCl3/AlCl3 Catalyst Systems. I. Effects of the Polymerization Conditions on the Copolymerization Products

Abstract

The copolymerization products of α-pinene and styrene were prepared with the compound catalyst system SbCl₃/AlCl₃ by changing the Sb/Al ratio, feeding monomer ratio, solvent, and polymerization temperature. The compositions of the copolymerization products were quantitatively characterized by the method of the combination of micro-ozonization and thin-layer chromatography in terms of the contents of the homopolymers and the copolymers containing high or low mole fractions of α-pinene, the yields of pure copolymer, and the monomer unit ratios (F ₁) of copolymers. The results show that it was easier to obtain the higher yield (up to 80%) of the pure copolymer with the complex catalyst system than with AlCl₃ alone. The F ₁ values could be controlled between 30 and 56% under the following polymerization conditions: Sb/Al  1/2, α-pinene/styrene  70%, and the conversion of styrene  90%.     

Polymerization Kinetics of Propylene with the MgCl_2-Supported Ziegler-Natta Catalysts——Active Centers with Different Tacticity and Fragmentation of the Catalyst

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_4/MgCl_2 Ziegler-Natta(Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant k_p, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature(60 ℃) resulted higher activity, k_p and lower [C*], and the isotactic active centers C_i* as the majority ones producing the highest isotactic polypropylene(iPP) components showed much higher k_p when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.     

Efficient Room‐Temperature Synthesis of Tri‐ and Tetrasubstituted Imidazoles Catalyzed by ZrCl4

A general protocol has been developed for the rapid synthesis of 2,4,5‐trisubstituted and 1,2,4,5‐tetrasubstituted imidazoles in high yields using ZrCl₄ as an efficient catalyst at room temperature. A variety of aromatic, aliphatic, and terpenoidal aldehydes underwent condensation with NH₄OAc/amines to give the imidazoles. Similarly, the imidazole glycoconjugates are prepared in good yields from the corresponding glycosyl aldehydes.     

Polymerisation of dithiocarbamates by oxidative coupling using iodine as oxidant—I. Synthesis and characterisation

A novel polymer has been synthesised by reacting hexamethylene diamine with carbon disulphide by the oxidative coupling method using iodine as oxidant. The first step of the polymerisation involves the formation of dithiocarbamate by reacting a diamine with carbon disulphide in alkaline medium at low temperature (5–10°) in a protic solvent such as alcohol or water. Next, the dithiocarbamate is coupled with a diamine using iodine as the oxidant at ambient temperature. The polymerisation proceeds by a radical mechanism. The molecular weight of the polymer is not very high (∼ 12,000); it is soluble in polar solvents. It was characterised by elemental analysis (N, S) and i.r. and NMR spectroscopy. The physical characteristics have been studied.     

Chemoselective Benzylation and Allylation of 4-Nitrobenzaldehyde Promoted by Phase Transfer Catalyst and Metal in Aqueous Media

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Influence of Polar Modifiers on Microstructure of Polybutadiene Obtained by Anionic Polymerization. Part 2: Lewis Base (σ) Amine-Ether and Ether-Type Polar Modifiers

The influence of Lewis base (σ complex) amine-ether and ether-type polar modifiers on the microstructure of polybutadiene obtained by anionic polymerization was studied. Analysis of FT-IR-ATR, ¹H, and ¹³C NMR spectral data for polybutadienes obtained in the presence of the complexing agents showed that increase of concentration of all tested polar modifiers very strongly promoted formation of 1,2 butadiene isomeric structures, especially increasing the content of vinyl–vinyl and vinyl–trans-1,4 diads.     

Copolymerization of Ethylene/1-Butene with Heterogeneous TiCl4/(α-Diimine)nickel(Ⅱ) Complex Combined Catalyst

The new type heterogeneous combined catalyst system TiCl4-(α-diimine)nickel(Ⅱ) complexes/MgCl2-SiO2/AlR3 was prepared. Ethylene and 1-butene were copolymerized with the catalysts in slurry phase. It was found that with combined catalyst, the copolymers with lower density and higher branched degree were obtained. 13CNMR results showed that in the obtained copolymers existed not only ethyl but also some other kinds of branches due to the fact that ethylene exhibits the behavior of oligomerization and copolymerization in-situ with combined catalysts.     

Effect of a Carbon Promoter on the Properties of a Co/MgAlO4 Catalyst for Fischer–Tropsch Synthesis

Kinetics and Catalysis - The influence of carbon on the genesis of the active phase of cobalt in aluminum–magnesium spinel supported catalysts on their catalytic properties in the synthesis...     

Functional Monomers and Polymers. 165. Dehydrochlorination of Head‐to‐Tail 1,4‐rans‐Poly‐(‐1‐Chlorobutadiene) Prepared by Inclusion Polymerization in Deoxycholic Acid Canals

Thermal and chemical dehydrochlorination of head‐to‐tail 1,4‐trans‐poly(‐1‐chlorobutadiene) prepared by inclusion polymerization in deoxycholic acid canals resulted in formation of a trans‐polyacetylene‐type polymer. The dehydrochiorinated polymer was characterized by UV/VIS, IR, Raman, and ESR spectroscopy. The number of conjugated double bonds in the polymer was about 10–20. Doping with iodine was also studied.     

Facile Sol-Gel Synthesis of Co3O4 Nanoparticles — An Efficient and Recyclable Catalyst for the Synthesis of 1,2-Disubstituted Benzimidazoles Under Solvent-Free Conditions

Russian Journal of Organic Chemistry - High-surface-area Co3O4 nanoparticles have been prepared as a potential heterogeneous catalyst by the sol-gel method using starch as an inexpensive and a...     

Inelastic electron tunnelling spectroscopy—I. Construction and operation of the spectrometer

Inelastic electron tunnelling spectroscopy (IETS) provides a means of obtaining information on vibrational and electronic modes requiring only μg quantities of sample. The essential electronic, cryogenic and high vacuum systems for the construction and operation of an inelastic electron tunnelling spectrometer are described. Methods for introducing the sample to be studied (“doping”) are considered along with the potential chemical applications of this technique.     

Synergistic Effects of the ZnCl2-SiCl4 Modified TiCl4 /MgCl2 /THF Catalytic System on Ethylene/1-Hexene and Ethylene/1-Octene Copolymerizations简

The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl4 /MgCl2 /THF catalysts modified with different metal halide additives(ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl2-SiCl4 revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C―O―C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl4 /MgCl2 /THF catalytic system leading to an increase in activities as well as comonomer insertion(as proven by13C-NMR). However, Lewis acidmodifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnCl2 and/or SiCl4 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of α-olefins insertion, regardless of the types of Lewis acids and comonomer.     

Comparison of intermediates of tryptophan, tyrosine and their dipeptide induced by UV light and SO. 4 –

The chemical processes of tryptophan (Trp), tyrosine (Tyr) and a dipeptide Trp-Tyr, which are induced by UV radiation and one-electron oxidation of SO^. ₄ ^–, have been investigated in aqueous solution by KrF (248 nm) laser flash photolysis. On the basis of optical studies, the photoionization of Trp and Tyr produces the tryptophan indolyl radical and tyrosine phenoxyl radical, respectively, and these are different from the intermediates resulting from interaction of Trp and Tyr with SO^. ₄ ^–. In the case of Trp, SO^. ₄ ^– would attack the indole moiety to produce a C(2)-yl sulphate radical adduct, and Tyr is oxidized to produce mainly the corresponding one-electron oxidized radical, which deprotonates rapidly to form the phenoxyl radical in neutral solution, and a possible sulphate radical adduct. From transient absorption spectra of photoionization of Trp-Tyr, an intramolecular electron transfer, Trp/N^.-Tyr Trp-Tyr/O^., has been observed, but there was no observation of the process of one-electron oxidation of Trp-Tyr by SO^. ₄ ^–.     

Unusual Extensional Rheology and Dispersion Behavior of High Impact Polystyrene/TiO2 Nanocomposites Prepared by Melt‐Compounding

The extensional rheology and dispersion behavior of high impact polystyrene (HIPS) and HIPS/TiO₂ nanocomposites prepared by melt‐compounding were investigated. The influence of ethylene‐vinyl acetate (EVA) copolymer on the extensional rheology of HIPS/TiO₂ masterbatches was also researched. The rheological experiments investigated with Rosand Presicion Rheometer confirmed that the HIPS/TiO₂ masterbatches, the HIPS/EVA/TiO₂ masterbatches and the HIPS/TiO₂ nanocomposites with low TiO₂ loading shown different extensional rheology in comparison to the pure HIPS. Field‐emission scanning electron microscopy (FE‐SEM) shown the dispersion morphology of TiO₂ nanoparticles in HIPS based nanocomposites and indicated the influence of TiO₂ dispersion behavior on the unusual extensional rheology of HIPS nanocomposites.     

A Critical Evaluation of Bond Energy/ Group Contribution Methods of Calculating the Heat of Formation: Development of a New Generalized Scheme. Part I. Alkanes∗

Results of application of seven well-known bond energy/group contribution methods to the experimental data on heats of formation of 70 alkanes, including a few polymers, are reported. The earlier claims of accuracy of many of these schemes become untenable with the emergence of new data on nonanes and polymers, calling for more parameters to cope with the steric interaction energy in higher branched alkanes. A new general bond energy scheme is developed with low standard error of ±0.28 kcal/mole which is close to the experimental uncertainty. Heats of formation of some polyolefin structures are predicted for the experimental verification in the future. The energy terms of the new scheme are transferable to other non-hydrocarbon organic compounds for which a general scheme is under way.     

The binary system benzene—hexafluorobenzene studied by SSOZ theory and computer simulation. I. The charge symmetry model

The symmetry reduction of the SSOZ equation already developed for pure components is extended to binary mixtures. The general formalism is applied to the binary system C₆F₆/C₆H₆, whose “mixing interaction” is described by a simplified “charge symmetry model”. Varying the charge strength in a systematic way the predictions of SSOZ theory are verified by extensive computer simulation (molecular dynamics) studies. Thereby mixtures and pure components are treated in a unified way. Finally, extensions of the “charge symmetry model” are presented and the computed radial excess correlation functions are compared to those measured by neutron and X-ray scattering.