Preparation and thermal degradation kinetics of terpolymer poly(?-caprolactone-co-1,2-butylene carbonate)

Poly(?-caprolactone-co-1,2-butylene carbonate) (PBCCL) was successfully synthesized via terpolymerization of carbon dioxide, 1,2-butylene oxide(BO) and ?-caprolactone (CL). A polymer-supported bimetallic complex (PBM) was used as catalyst. The influences of various reaction conditions such as reaction content, reaction time and reaction temperature on properties of terpolymers were investigated. When CL content increased, the viscosity-average molecular weights (M_v), glass transition temperature (T_g) and decomposition temperature (T_d) of PBCCL improved relative to those of poly(1,2-butylene carbonate) (PBC). Prolonging the reaction time resulted in increase in M_v and T_g. As reaction temperature increased, the molar fractions of CL (fCL) increased obviously. When the reaction temperature went beyond 80 °C, the resulting copolymers tended to be crystalline. The thermal properties and degradation behaviors of PBCCL were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The apparent activation energy and thermal degradation model of PBCCL was estimated by means of Ozawa-Flynn-Wall method and Phadnis-Deshpande method, respectively. The results showed that T_g and T_d of the terpolymer PBCCL were much higher than those of PBC. The thermal degradation behavior of PBCCL was evidenced by one-step thermal degradation profile. The average apparent activation energy is 77.06 kJ/mol, the thermal degradation kinetics follows the power law thermal decomposition model.     

Rheological study on the cure kinetics of two-component addition cured silicone rubber

The cure kinetics for two-component silicone rubber formed by addition reaction was studied by the rheological method. The influence of reaction temperature (T) on the cure kinetics was explored in detail. It was observed that the data of gel time (t _gel, i.e. the time when the reaction reaches the gel point) or a specific reaction time (t _nc) (defined as the reaction time before which time the influence of confinement of network on the diffusion of reaction components can be neglected) versus T obey certain functional relationship, which was well explained by the cure kinetics model of thermoset network. The cure kinetics for the two-component silicone rubber can be well fitted by the Kamal-Sourour(autocatalyst) reaction model rather than Kissinger model. When the reaction time was before or equal to t _nc, the reaction order obtained by the Kamal-Sourour reaction model was 2, which was consistent with the reaction order inferred from the two components chemical reaction when the diffusion of reaction components was not influenced by the formed cross-linked polymer network. When the reaction time was larger than t _nc, such as to the end of reaction (t _e), the influence of confinement of network on the diffusion of reaction components cannot be neglected, and the reaction order obtained by the Kamal-Sourour reaction model was larger than 2. It was concluded that the confinement effect of network had a greater influence on the cure kinetics of the silicone rubber. The reaction rate constants (k _r) under different temperatures were also determined by Kamal-Sourour reaction model. The activation energy (E) for the two-component silicone rubber was also calculated from the results of lnt _gel, lnt _nc, and lnk _r versus 1/T, respectively. The three values of E were close, which indicated that above analyses were self-consistent.     

Synthesis and reactivity of subvalent compounds. Part 13: Reaction of triethyl orthoformate with amines and selenium—a convenient one-step three-component synthesis for selenoureas

Selenoureas are obtained by a novel three-component condensation reaction from metallic selenium, triethyl orthoformate and a primary or secondary amine. The reaction is carried out as solvent-free one pot-procedure at 180-190°C under inert gas with a reaction time of 8 h. The reaction was tested for piperidine, isopropylamine, N,N′-dimethylpropylenediamine (Me-NH-CH₂-CH₂-CH₂-NH-Me) and N,N′-disubstituted ethylenediamines (R-NH-CH₂-CH₂-NH-R, R=Me, Et, ⁱPr, ^tBu, Ph).     

Rare direct imidation of aromatic metallacycle by reaction of CpCo(dithiolene) complex with N-halosuccinimide

The aromatic [CpCo(S₂C₂(R)(H))] (R = Ph, Me, 9-phenanthryl, H) complexes reacted with N-halosuccinimides (NXS; X = Cl, Br, I) in carbon tetrachloride at room temperature to undergo the N-succinimide substitution reaction on the dithiolene ring, but no halogenated dithiolene complex was obtained. The imidation products [CpCo(S₂C₂(R)(N-sccinimide))] were yielded up to 64% where X = I and R = 9-phenanthryl. The reaction of [CpCo(S₂C₂(Ph)(H))] with N-bromophthalimide (NBP) also gave the imidation product [CpCo(S₂C₂(Ph)(N-phthalimide))]. This is the rare direct imidation reaction to an aromatic metallacycle by NXS. The reaction of [CpCo(S₂C₂H₂)] (R = H) with NIS afforded the double imidation product. One by-product in this reaction was the dithiolene-dithiolene homo-coupling product [CpCo(S₂C₂(R))]₂ (R = Ph, Me, 9-phenanthryl). The microwave-enhanced (MW) reactions were attempted in the carbon tetrachloride solution. Although the solution temperature increased up to only 43 °C by MW irradiation, the imidation reaction worked with short reaction time.     

One-step synthesis of pentavalent triphenylantimony derivatives Ph3Sb(OSiR3)2, Ph3Sb(OCH2CH2)2NH and Ph3Sb(OCH2CH2NMe2)2: X-ray molecular structure of Ph3Sb(OSiMe3)2

Pentavalent bis(triorganosiloxy)triphenylantimony derivatives, Ph₃Sb(OSiR₃)₂ (R = Me, Ph), were synthesized by reaction of triphenylantimony with trimethyl- or triphenylsilanol in the presence of tert-butylhydroperoxide by the mild reaction conditions (0-5 °C, 2 h). The reaction of triphenylantimony with diethanolamine in the presence of tert-butylhydroperoxide gave the cyclic compound Ph₃Sb(OCH₂CH₂)₂NH. The mixture of Ph₃SbO and Ph₃Sb(OCH₂CH₂NMe₂)₂ was obtained by the reaction of triphenylantimony with 2-(N,N-dimethylamino)ethanol in the presence of tert-butylhydroperoxide.     

The production of H(2S) atoms in the energy-transfer reaction of O2(1Δg) with HO2(X̃2A″)

The reaction of O₂(¹Δg) with HO₂(X?) was studied in an isothermal flow reactor in the pressure range 7?p? 10.7 mbar at temperatures between 299?T? 423 K. H-atom production was observed in the reaction O₂(¹Δg) + HO₂(òA′) - H(²S)+ 2O₂ (³Σ_g^?). The rate of this reaction (k₁) is estimated to be k₁ = (1 ± 0.5) × 10¹⁴ CM³ Mol^?1 s^?1. The implications of this reaction to recent determinations of the rate of the reaction H + O₂(¹Δg) are discussed.     

On the structure and cure acceleration of phenol-urea-formaldehyde resins with different catalysts

Phenol-urea-formaldehyde (PUF) resins with different catalysts [calcium oxide (CaO), sodium carbonate (Na₂CO₃), zinc oxide (ZnO), and magnesium oxide (MgO)] were prepared to accelerate the cure of the resin at low temperature. The cure-acceleration effects of catalysts on chemical structure and cure characteristics of PUF resins were investigated by using both liquid ¹³C nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The liquid ¹³C NMR analysis indicated that the catalyst such as CaO seemed to present a retarded effect on the polycondensation reaction of phenolic components with urea units, while the Na₂CO₃ appeared to promote the self-condensation reaction of phenolic methylol groups at para position toward the formation of para-para methylene linkage. Both ZnO and MgO in PUF resins promoted self-condensation reaction of para methylol groups and condensation reaction of ortho methylol groups with para methylol groups. The catalysts such as Na₂CO₃, ZnO, and MgO can make PUF resins cure at a low temperature. Among these catalysts, the MgO had the most significant accelerating effect on polycondensation and cure reaction of PUF resin.     

Reactions of O with CO van der Waals molecules and clusters

The reaction of O(³ P) with COR _m clusters to produce electronically excited CO₂ was studied under molecular beam conditions. It was found that the spectrum of the chemiluminescence produced extended from the blue all the way to the near infrared. The dependence of the total emission intensity on stagnation pressure was investigated for (CO) _m as well as for COR _m , R=He, Ne, Ar, N₂, CO₂ and SO₂. The low pressure data indicate that small (CO) _m polymers are more efficient than clusters of CO with other species in inducing the chemiluminescent reaction. The larger CO-rare gas clusters, however, exhibited larger reaction cross-sections than those of the CO polymers. Rare gas clusters ofm≧5, on the other hand have successively smaller cross sections for reaction. The reactivity of the CO₂ and SO₂ clusters seems to peak at aboutm=1 and then decreases for larger species. An equilibrium model for cluster formation was proposed and it was found capable of explaining and simulating the experimental observations. Contrary to what was reported from afterglow experiments, no barrier for the reaction was detected.     

Hydrothermal synthesis and thermodynamic analysis of dawsonite-type compounds

Dawsonite-type compounds of formula MAl(OH)₂CO₃ (M=Na,K,NH₄) were hydrothermally synthesized. The influences of the composition of starting materials, reaction temperature, acidity of the reaction medium on the formation, morphology and particle size of MAl(OH)₂CO₃ powders were systematically investigated. The experiment results show that increase in the amount of MHCO₃ favors the formation of MAl(OH)₂CO₃ phase with more slender particle morphology. The higher the reaction temperature, the grosser the particle is. It was also demonstrated that the particle size of the MAl(OH)₂CO₃ phase are most uniform when the pH value of reaction system is 10.3 for sodium dawsonite and potassium dawsonite, but it is 9.79 for that of ammonium dawsonite. The thermodynamics of the formation of dawsonite-type compounds have also been analyzed in details.     

Synthesis,characterization, and catalytic application of a zinc(II) complex bearing a pyrazole-based ligand

The reaction between ZnCl₂ and N,N-bis[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]-1-phenylethylamine (bdmppea) affords [(bdmppea)ZnCl₂], whose structure has been determined by X-ray crystallography. The [(bdmppea)ZnEt₂] complex in situ prepared by the reaction between [bdmppea] and ZnEt₂ exhibited high activity toward the polymerization reaction of rac-lactide at room temperature. However, its activity decreased sharply with decreasing temperature. Stereospecificity of this catalyst characterized by heterotacticity (P_r) was determined by homonuclear decoupled NMR spectroscopy, which value was ∼0.58.     

Adiabatic explosion in the flash photolysis of CIFCl2H2 mixtures

Incubation period and explosive limits in the flash photolysis of a CIFCl₂H₂ mixture has been measured. The ratio of rate constants k₃₁/k₁₃ for the reversible reaction Cl+CIF α Cl₂ + F (k₁₃ is the rate constant for the forward reaction, k₃₁ for the back reaction) was measured: k₃₁/k₁₃ = 270 ? 65 (T = 295 K). Photothermal explosion theory has been generalized for the case of a chain process with the three active centers.     

Electron spin resonance studies of ziegler-natta-type catalysts. The complex derived from dichlorobis (η-cyclopentadienyl) vanadium (Cp2VCl2) with ethylaluminium sesquichloride to polymerize ethylene

The reaction between Cp₂VCl₂ (Cp = η-cyclopentadienyl) in CH₂Cl₂ and Et₃Al₂Cl₃ or Et₂AlCl in η-heptane yields three paramagentic species giving the ESR parameters a_γ = 4.11 mT, g = 1.991 (I); a_γ = 7.46 mT, g = 1.982 (II); a_γ = 7.398 mT, g = 1.985 (III). Ethylene was polymerized using these catalysts; the solution was examined by the electron spin resonance technique before the polymerization and during the course of the reaction. The catalyst activity decayed quickly, and the mechanism of the reaction is discussed.     

Synthesis of cis bis-β-lactams via Staudinger cycloaddition reaction using C2-symmetric 1,2-diamines

An efficient stereoselective synthesis of bis-β-lactams via cycloaddition reaction (Staudinger reaction) of ketenes with bisimines derived from C₂-symmetric 1, 2-diamines is described. The reaction provided diastereomeric mixture of meso and C₂-symmetric cis-bis-β-lactams with higher selectivity for meso-bis-β-lactams.     

Thermoanalytical investigations on the solid-state synthesis of Sr-doped praseodymium alkaline-earth cobalt oxides

In this study, the formation and characteristics of Sr-doped praseodymium alkaline-earth cobalt oxide were studied as a function of the strontium content (x). PrBa_1?x Sr _x Co₂O_5+d ceramics with x?=?0.0, 1/16, 1/8, 1/4, and 1/2.5 were prepared by solid-state reaction method from Pr₆O₁₁, BaCO₃, SrCO₃, and Co₃O₄. The solid-state reaction mechanisms were analyzed by differential thermal analysis (DTA) and thermogravimetry (TG) techniques to characterize properly the distinct thermal events occurring during synthesis of layered perovskite-type PrBa_1?x Sr _x Co₂O_5+d oxides. The X-ray diffraction (XRD) results were used to assist the interpretation of DTA?CTG analyses. The TG, DTA, and XRD results for the mixtures showed that the solid-state reaction between precursors was completed in a temperature range between 800 and 1000?°C. The strong influence of strontium contents (x) on the solid-state reaction temperatures and PrBa_1?x Sr _x Co₂O_5+d structure was found.     

The reaction of (Sp)-2-(diphenylphosphino)ferrocenecarboxylic acid with carbodiimide reagents: Characterisation of the acid anhydride and urea products

Interaction of (S_p)-2-(diphenylphosphino)ferrocenecarboxylic acid [(S_p)-1] with N,N′-dicyclohexylcarbodiimide (DCC) and N-ethyl-N′-[3-(dimethylamino)propyl]carbodiimide (EDC) have been investigated in order to study the reacting system itself and to characterise side-products typically arising during the diimide-promoted condensation of acid (S_p)-1 with nucleophiles. The reaction between (S_p)-1 and DCC was found to give preferentially the respective urea derivative in the absence of a base, and (S_p)-2-(diphenylphosphino)ferrocenecarboxylic anhydride [(S_p,S_p)-3] when the same reaction was performed in the presence of 4-(dimethylamino)pyridine (DMAP). With EDC, the preference for a reaction pathway was less pronounced: whereas the reaction without the base afforded exclusively the corresponding urea, that in the presence of DMAP yielded a mixture of the urea and anhydride (S_p,S_p)-3.     

Development of radical addition-cyclization-elimination reaction of oxime ether and its application to formal synthesis of (±)-martinelline

Radical addition-cyclization-elimination (RACE) reaction of oxime ether carrying unsaturated ester provides a novel method for the construction of pyrroloquinoline. Treatment of oxime ethers with Bu₃SnH and AIBN gave N-norpyrroloquinoline as a major product, which was also obtained by the radical reaction of the corresponding hydrazone and imine. The radical reaction of aldehyde and ketone carrying unsaturated ester proceeded stereoselectively to give cis-furoquinolines and cis-hydroxyesters. The RACE reactions by using each of Bu₃SnNMe₂, Bu₃SnD, and/or D₂O were also examined in order to propose a reaction pathway to N-norpyrroloquinoline. Furthermore, the synthetic utility of RACE reaction is demonstrated by preparation of a key intermediate for the synthesis of (±)-martinelline.     

Alkynylcyanation of alkynes and dienes catalyzed by nickel

Alkynyl cyanides are found to add across alkynes and 1,2-dienes in the presence of a catalyst prepared in situ from Ni(cod)₂, xantphos, and BPh₃. A range of functionalized conjugated cis-enynes are obtained with high regioselectivity. The addition reaction across norbornadiene proceeds in the absence of BPh₃ to give exo-cis adduct exclusively. A stoichiometric reaction of an alkynyl cyanide, Ni(cod)₂, xantphos, and BPh₃ gives trans-(xantphos)Ni(CNBPh₃)(CCSiMe₂t-Bu), which is suggested to be a plausible reaction intermediate of the alkynylcyanation reaction.     

Au_n团簇催化水煤气变换反应机理的密度泛函理论研究

利用密度泛函理论(DFT)研究了Au10、Au13和Au20三类团簇的稳定性和对水煤气变换(WGSR)反应的催化活性,考察了各物质在Aun团簇上的吸附行为和微观反应机理。结果表明,三类Aun团簇的稳定性顺序为Au10Au13Au20,而Aun团簇中电子离域性及吸附能力大小趋势为Au13Au10Au20。在三类Aun团簇上,水煤气变换反应的控速步骤均为H2O的解离,但其反应机理路径有所不同。Au10团簇上为羧基机理,COOH*中间体直接解离;Au13团簇上为氧化还原机理,两个OH*发生歧化反应;Au20团簇上为羧基机理,COOH*和OH*发生歧化反应。通过对三类团簇上的最佳反应路径进行比较发现,Au13团簇在低温下具有较好的催化活性。     

Studies on the intermolecular interactions of metal chelate complexesVIII: On the interactions of dithiocarbamato-copper(II) and -copper(I) complexes with haloalkanes

The interaction of Cu(II)(dtc)₂ and Cu(I)(dtc) complexes with haloalkanes were studied by the EPR method. It was found that the Cu(II)(dtc)₂ complex reacted with haloalkanes only in the presence of weak Lewis bases which formed adducts with it. The intermediate reaction product is the mixed-ligand complex Cu(II)(dtc)X_n (X = Cl, Br, n = 1 or 2); the final products being CuX₂B_n (B = Lewis bases, n = 1 or 2) and unstable resin-like residue. Cu(I)(dtc) reacted with haloalkanes without any promoters giving the mixed-ligand complex Cu(II)(dtc)X_n as product. Free radicals were detected in the reaction of Cu(I)(dtc) using the method of “radical scavenger” and were not found in the reaction of Cu(II)(dtc)₂. The reported results confirmed one of the two reaction mechanisms proposed in the previous studies. The role of the solvent on the EPR parameters of the mixed-ligand Cu(II)(dtc)X complex is also discussed.     

Design of postmetallocene catalytic systems of arylimine type for olefi n polymerization: XV. Synthesis of (N-Aryl)salicylaldimine ligands containing a but-3-enyloxy group and their complexes with titanium(IV) dichloride

A series of (N-aryl)salicylaldimines was synthesized by the reaction of salicylaldehydes substituted in the positions 3 and 5 by bulky tert-butyl or α-cumyl groups with hydrochlorides of o-, m-, and p-(but-3-enyloxy) aniline in the presence of triethylamine. The obtained compounds formed by the reaction with TiCl₂(OPr-i)₂ complexes of titanium(IV) dichloride L₂TiCl₂.