Cationic polymerization of isobutylene coinitiated by AlCl3 in the presence of ethyl benzoate

<正>The cationic polymerizations of isobutylene(IB) coinitiated by AlCl_3 were carried out in solvent mixture of n-hexane /methylene dichloride(n-hex/CH_2Cl_2) of 60/40 V/V in the presence of ethyl benzoate(EB) at various temperatures range from-80℃to-30℃.The effects of EB concentration([EB]) and polymerization temperature on monomer conversion,weight-average molecular weight(M_w) and molecular weight distribution(MWD,M_w/M_n) of polyisobutylene (PIB) products were investigated.The rate of polymerization decreased while M_w of PIB products increased with increasing [EB].The polymers with high molecular weight could be prepared in the presence of a suitable amount of EB.Significantly, the polymers with high M_w of 80.2×10~4 and 65.4×10~4 could be produced at-80℃and-70℃at[EB]=0.24×10~(-3) mol/L respectively,which were much higher than that(M_w=57.9×10~4) of PIB prepared at-100℃in the absence of EB.A simple but effective method for preparing the high molecular weight polyisobutylenes was developed in this work.It has been also found that the activation energy for propagation(E_p) depended on the polymerization temperature range in the presence of EB.An obvious inflection of the linear plots of lnX_n versus 1/T_p occurred at the temperature range from-60℃to-50℃at four different concentrations of EB from 0.19×10~(-3) mol/L to 0.33×10~(-3) mol/L,and thus the inflection temperature(T_(inf)) was in the range of-60℃to-50℃.When[EB]was in the range of 0.24×10~(-3) mol/L to 0.33×10~(-3) mol/L,E_p was determined to be around-12 kJ/mol when the polymerization was carried out at temperatures from-80℃to T_(inf) and to be around-28 kJ/mol at temperatures from T_(inf) to-15℃respectively.     

Study on cationic polymerization of isobutylene using electrochemical method

The cationic polymerization of isobutylene (IB) initiated by H₂O/TiCl₄ was carried out in a mixture of methylene dichloride and n-hexane at −60 °C in the presence of a variety of external electron pair donors (EDs), such as triethylamine (TEA), N,N-dimethyl acetamide (DMA) and pyridine (Py). The effects of ED concentration ([ED]), H₂O concentration ([H₂O]) on conductance and capacitance in H₂O/TiCl₄/ED/CH₂Cl₂ reaction system were investigated. The effects of [ED], [H₂O], solven polarity and polymerization time on monomer conversion, molecular weight (MW), molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) were also investigated. Conductance decreased while capacitance increased with increases in both [ED] and electron donicity of ED. Conductance and capacitance increased with [H₂O] when [H₂O] was more than [Py]. Both unpaired and paired ions existed as propagating species or chain carriers in the presence of relatively low [ED] and polymers with bimodal molecular weight distribution (peak a and b) were obtained. The peak a with high molecular weight was induced by propagation via unpaired ions while peak b with low molecular weight was induced by propagation via paired ions. The propagation via paired ions could be achieved and polymers with unimodal molecular weight distribution could be produced when sufficient amounts of external ED was introduced to polymerization system.     

Cationic polymerization of dienes VII. New electron donors in the polymerization of 1,3-pentadiene initiated by aluminum trichloride in non-polar solvent

The aim of this research was to investigate new bulky electron donors (EDs) generating hindered active species in the cationic polymerization of 1,3-pentadiene initiated by AlCl₃ in pentane, in order to avoid or strongly reduce the reaction between the active species and the double bonds of the polymer which are responsible for side reactions. At room temperature, the polymerization in the presence of new ED, such as OPh₂, N(PhBr)₃, NPh₃ and SPh₂, allowed to obtain higher conversions and lower insoluble fractions than without electron donor. The formation of a complex ED/AlCl₃ was shown for each electron donor. However, in the case of NPh₃ and SPh₂, variations of the polymer microstructure demonstrated an interaction between active species and these EDs. Similar results were obtained at lower temperature (−10 °C). The beneficial effect of the presence of electron donors such as NPh₃ and SPh₂ demonstrated the validity of the concept of sterically hindered active species, but the polymerization was still uncontrolled.     

Kinetic and mechanistic study of the quasiliving cationic polymerization of styrene with the 2-phenyl-2-propanol/AlCl3 · OBu2 initiating system

The cationic polymerization of styrene with the 2-phenyl-2-propanol (CumOH)/AlCl₃ · OBu₂ initiating system at various dibutyl ether concentrations in a mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at −15 °C was investigated. The experimental results showed that an increase in dibutyl ether concentration leads to a noticeable decrease in the polymerization rate as well as to the more controlled polymerization in terms of molecular weight (M_n) and molecular weight distribution (MWD) evolutions. The kinetic investigation revealed that the polymerization proceeds in two stages. The first stage is characterized by high polymerization rate and slow initiation relative to propagation. During this stage molecular weight decreases or does not change and MWD increases with conversion. In the second stage considerably slower quasiliving polymerization of styrene occurs. The quasiliving nature of the styrene polymerization by the CumOH/AlCl₃ · OBu₂ system is proved and mechanistic scheme of the polymerization is proposed.     

(CH3)3SiCl/TiCl4 INITIATING SYSTEM FOR CATIONIC POLYMERIZATION OF 1,3-PENTADIENE

Cationic polymerizations of 1,3-pentadiene (PD) initiated by trimethylsilyl chloride (TMSCl) incombination with TiCl_4 were carried out in n-hexane at 30℃. The yield of polymer was greatly increased bythe addition of TMSCl, indicating that the TMSCl/TiCl_4 combination is an efficient initiating system for PDcationic polymerization. However, the introduction of TMSCl gave rise to a drop in the molecular weight ofthe polymer. Kinetic results demonstrated that the polymerization initiated by TMSCl/TiCl_4 is 4.5 times fasterthan that induced by TiCl_4 alone. Various ethers were used to mediate the TMSCl/TiCl_4 initiating system.Adding diphenyl ether could increase both the yield and molecular weight of the polymer. Structural evidenceillustrates that the polymerization is indeed initiated by TiCl_4 in combination with HCl resulting fromhydrolysis by adventitious water.     

Controlled/living cationic polymerization of styrene with BF3OEt2 as a coinitiator in the presence of water: Improvements and limitations

The controlled/living cationic polymerization of styrene using R-OH/BF₃OEt₂ (R-OH = 1-phenylethanol (1), 2-phenyl-2-propanol (2) and 1-(4-methoxyphenyl)ethanol (3)) at 0 °C in CH₂Cl₂ and in the presence of water was investigated. With 1/BF₃OEt₂, the poor control over molecular weight and molecular weight distribution was ascribed to a competitive protonic initiation induced by water. The molecular weight of the polymers obtained with 2/BF₃OEt₂ and 3/BF₃OEt₂ at low water content ([H₂O] ? 0.11 M) increased in direct proportion to the monomer conversion in agreement with the calculated values, assuming that one initiator molecule generates one polymer chain, but the molecular weight distribution was found relatively broad (M_w/M_n ∼ 1.8). ¹H NMR analyses confirmed that polymerization proceeds via reversible activation of C-OH terminus, but some loss of hydroxyl functionality was revealed. Some trials using high water contents in the recipe ([H₂O] ? 1.6 M) produced only traces of polymer due to catalyst decomposition.     

Investigation of the effect of epoxide structure on the initiation efficiency in isobutylene polymerizations initiated by epoxide/TiCl4 systems

The effect of the chemical structure of styrene-based epoxides, namely, styrene epoxide (SE), α-methylstyrene epoxide (MSE), p-methylstyrene epoxide (pM-SE) and α-methyl-p-methylstyrene epoxide (pM-MSE), in conjunction with TiCl₄, on the initiation efficiency (I_eff) in the carbocationic polymerization of isobutylene (IB) was investigated. SE yielded living polymerization, but the initiation efficiency was low when compared to MSE (I_eff=8% and 35%, respectively). pM-SE led to non-living IB polymerization, while pM-MSE revealed linear M_n-conversion plot and narrow MWD with a non-linear first order rate plot. Among the epoxides investigated, MSE was the best initiator to scale up the one-step synthesis of polyisobutylenes (PIBs) carrying one primary hydroxyl head group and one tertiary chloride end group. The hydroxyl functionality of these PIBs determined by ¹H-NMR was F_n=1.09±0.16 from 24 experiments.     

The dehydration of ZnSO4·7H2O and NiSO4·6H2O

Using differential scanning calorimetry (DSC) in combination with effluent analysis, differential thermal analysis (DTA), thermogravimetric analysis (TG) and X-ray analysis, the dehydration of ZnSO₄·7H₂O and NiSO₄·6H₂O was investigated and a few transition enthalpies were measured. The dehydration of both compounds showed a great analogy. For NiSO₄·6H₂O the α—β phase transition was studied.The dehydration scheme of both hydrates can be given as follows:

     

Heat capacity and thermodynamic functions of MnBr2 · 4H2O and MnCl2 · 4H2O

The heat capacities of MnBr₂ · 4H₂O and MnCl₂ · 4H₂O have been experimentally determined from 10 to 300 K. The smoothed heat capacity and the thermodynamic functions (H°_TH°₀) andS°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in these data is thought to be less than 1%. A subtle heat capacity anomaly was observed in MnCl₂ · 4H₂O over the temperature range 52 to 90 K. The entropy associated with the anomaly is of the order 0.4 J/mole K.     

Cationic polymerization of 1,3-pent adiene in the presence of arenes

The cationic polymerizations of 1,3-pentadiene initiated by AlCl3 in n-hexane at 30℃ have been carried out in the presence of various arenes,i.e.,benzene,toluene,p-xylene,o-xylene,m-xylene and mesitylene.The presence of all these arenes have reduced in different degrees the formation of crossliuked products.Namely,the crosslinking reaction,a major side-reaction during the cationic polymerization of 1,3-pentadiene,has been suppressed by adding the aromatic compounds.The results showed that a chain transfer to arene took place and this transfer process hindered the generation of the crosslinked polymer.IR and 1H NMR spectra have confirmed the existence of the corresponding aryl groups in the resulting polymers.     

Na4H3[SiW9Al3(H2O)3O37]·12H2O/H2O: a new system for selective oxidation of alcohols with H2O2 as oxidant

This work describes a catalytic system consisting of both Na₄H₃[SiW₉Al₃(H₂O)₃O₃₇]·12H₂O(SiW₉Al₃) and water as solvents (a small quantity of organic solvents were used as co-solvent for a few substrates) that can be good for selective oxidation of alcohols to ketones (aldehydes) using 30% H₂O₂ without any phase-transfer catalyst under mild reaction conditions. The catalyst system allows easy product/catalyst separation. Under the given conditions, the secondary hydroxyl group was highly chemoselectively oxidized to the corresponding ketones in good yields in the presence of primary hydroxyl group within the same molecule, and hydroxides are selectively oxidized even in the presence of alkene. Benzylic alcohols were selectively oxidized to the corresponding benzaldehydes in good yields without over oxidation products in solvent-free conditions. Nitrogen, oxygen, sulfur-based moieties, at least for the cases where these atoms are not susceptible to oxidation, do not interfere with the catalytic alcohol oxidation.     

Synthesis, structure, and properties of [Re2(HPO4)2(H2PO4)2(H2O)2] · 4H2O

The complex [Re₂(HPO₄)₂(H₂PO₄)₂(H₂O)₂] · 4H₂O (I) was synthesized and investigated by conductometric, potentiometric, electronic and vibration spectroscopic methods. Thermal behavior of the title compound was studied and its molecular structure was determined from X-ray diffraction data. In the dimeric neutral complex, the bridging pairs of the hydrophosphate and dihydrophosphate groups close four five-membered Re-O-P-O-Re chelate rings. The O atom of water molecule occupies the axial position in the metal coordination polyhedron. The Re-Re distance 2.2168(8) ? corresponds to quadruple bond. Original Russian Text ? A.V. Shtemenko, V.G. Stolyarenko, K.V. Domasevich, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 2, pp. 83–88.     

Cationic polymerization of 1,3-pentadiene and 2-methylpropene: Direct initiation is a general mechanism with AlCl3 in polar medium

Following previous results showing that direct initiation was operating in the cationic polymerization of 1,3-pentadiene in the presence of AlCl₃ in non-polar medium, it is shown on the same system that direct initiation also occurs in polar medium. In the case of 2-methylpropene the use of a proton trap (DtBP) allowed to show that at −30 °C, direct initiation mechanism was operating either in 64/36 or in 36/64 (v/v) CH₂Cl₂/pentane mixtures. These results show that direct initiation is a general mechanism with AlCl₃. SEC studies showed that for 2-methylpropene transfer can be minimized.     

Phase equilibria in the system Na,K,Mg,Ca∥SO4,Cl-H2O at 25°C in the crystallization regions of MgCl2·6H2O, CaCl2·6H2O, and 2MgCl2·CaCl2·12H2O

The translation method is used to study equilibria in the system Na, K, Mg, Ca∥SO₄, Cl-H₂O at 25°C in the crystallization regions of MgCl₂·6H₂O, CaCl₂·6H₂O, and 2MgCl₂·CaCl₂·12H₂O. The participation of these salts in the formation of the geometrical images of the title system is determined. The relevant fragments of the equilibrium phase diagram are designed. Original Russian Text ? L. Soliev, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 5, pp. 841–845.     

Pulse radiolysis study of trapped electron in MgSO4.7H2O single crystal

The single crystal of MgSO₄.7H₂O is very interesting to study the structure and kinetics of trapped electron in solids, because the hydrated salt has many H₂O molecules in the crystal lattice like water. The pulse radiolysis study of the trapped electrons in MgSO₄.7H₂O single crystal was carried out based on an electron linear accelerator. Two optical absorption peaks of the trapped electron in MgSO₄.7H₂O single crystal were observed: one is at the wavelength of 600 nm with a short lifetime of 81.4 ns; another is at 400 nm with a long lifetime of 1.06 μs. The kinetics of the trapped electron in the crystal was also compared with that in the aqueous solution.     

Coordination Polymers of Scandium Sulfate. Crystal Structures of (H2Bipy)[Sc(H2O)(SO4)2]2 · 2H2O and (H2Bipy)[HSO4]2

Compounds with the general formula Cat_x[Sc(H₂O)_z(SO₄)_y] · nH₂O (Cat = NH₄, H₂Bipy (Bipy is 4,4′-bipyridine), and HEdp (Edp is ethylenedipyridine) are synthesized and identified by elemental analysis and IR spectral data. The X-ray diffraction analysis of (H₂Bipy)[Sc(H₂O)(SO₄)₂]₂ · 2H₂O shows that in the structure of this compound, the chains of ScO₆ octahedra and SO₄ tetrahedra are united to form ribbons due to the tridentate coordination of the sulfate ion. The ribbons form a framework, whose infinite cavities contain H₂Bipy²⁺ cations.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 576–582.Original Russian Text Copyright © 2005 by Petrosyants, Ilyukhin, Sukhorukov.     

New open-framework in the uranyl vanadates A3(UO2)7(VO4)5O (A=Li, Ag) with intergrowth structure between A(UO2)4(VO4)3 and A2(UO2)3(VO4)2O

New uranyl vanadates A₃(UO₂)₇(VO₄)₅O (M=Li (1), Na (2), Ag (3)) have been synthesized by solid-state reaction and their structures determined from single-crystal X-ray diffraction data for 1 and 3. The tetragonal structure results of an alternation of two types of sheets denoted S for _∞²[UO₂(VO₄)₂]⁴⁻ and D for _∞²[(UO₂)₂(VO₄)₃]⁵⁻ built from UO₆ square bipyramids and connected through VO₄ tetrahedra to _∞¹[U(3)O₅-U(4)O₅]⁸⁻ infinite chains of edge-shared U(3)O₇ and U(4)O₇ pentagonal bipyramids alternatively parallel to a- and b-axis to construct a three-dimensional uranyl vanadate arrangement. It is noticeable that similar _∞[UO₅]⁴⁻ chains are connected only by S-type sheets in A₂(UO₂)₃(VO₄)₂O and by D-type sheets in A(UO₂)₄(VO₄)₃, thus A₃(UO₂)₇(VO₄)₅O appears as an intergrowth structure between the two previously reported series. The mobility of the monovalent ion in the mutually perpendicular channels created in the three-dimensional arrangement is correlated to the occupation rate of the sites and by the geometry of the different sites occupied by either Na, Ag or Li. Crystallographic data: 293 K, Bruker X8-APEX2 X-ray diffractometer equipped with a 4 K CCD detector, MoKα, λ=0.71073 Å, tetragonal symmetry, space group P4¯m2, Z=1, full-matrix least-squares refinement on the basis of F²; 1,a=7.2794(9) Å, c=14.514(4) Å, R1=0.021 and wR2=0.048 for 62 parameters with 782 independent reflections with I?2σ(I); 3, a=7.2373(3) Å, c=14.7973(15) Å, R1=0.041 and wR2=0.085 for 60 parameters with 1066 independent reflections with I?2σ(I).     

Hydrothermal synthesis, crystal structure and characterization of [Zn(H2O)4]2 [H2As6V15O42(H2O)]·2H2O

The compound [Zn(H₂O)₄]₂[H₂As₆V₁₅O₄₂(H₂O)]·2H₂O (1) has been synthesized and characterized by elemental analysis, IR, ESR, magnetic measurement, third-order nonlinear property study and single crystal X-ray diffraction analysis. The compound 1 crystallizes in trigonal space group R3, a=b=12.0601(17) Å, c=33.970(7) Å, γ=120°, V=4278.8(12) Å³, Z=3 and R1(wR2)=0.0512 (0.1171). The crystal structure is constructed from [H₂As₆V₁₅O₄₂(H₂O)]⁴⁻ anions and [Zn(H₂O)₄]²⁺ cations linked through hydrogen bonds into a network. The [H₂As₆V₁₅O₄₂(H₂O)]⁶⁻ cluster consists of 15 VO₅ square pyramids linked by three As₂O₅ handle-like units.     

Electronic transitions in Li4CoCl4.10H2O

The electronic spectrum of Li₄CoCl₆.10H₂O was recorded at liquid nitrogen temperature in the 4,000–25,000 cm^?1 spectral region. The simi larity of this spectrum to that of CoCl₂ permitted us to assume O_h syn metry of the [CoCl₆]^4? cluster in our sample. The band assignment was performed in the crystal field approximation using Tanabe and Sugano's energy matrices for Dq = 730 cm^?1, B = 820 cm^?1 and C/B = 4.4.The large number of bands and high intensity of the maxima in the regio 19,000–21,000 cm^?1 is discussed.