Optimal control determination of MMA polymerization in non-isothermal batch reactor using bifunctional initiator

In this work, we determine the optimal control for free-radical methyl methacrylate polymerization using a bifunctional initiator in a non-isothermal batch reactor. A detailed unsteady-state model of the process is employed. Four different optimal control objectives are realized, each of which optimizes a given variable simultaneously with the specification of another. The first two objectives involve the maximization of monomer conversion in a specified operation time, and the minimization of operation time for a specified, final monomer conversion. The last two objectives involve the maximization of monomer conversion for specified, final number and weight average polymer molecular weights. The temperature of heat-exchange fluid inside reactor jacket is considered as a control function of an independent variable. To meet the specification of an optimization variable other than time, the differential model of batch process is derived in the range of specified variable. Equations are provided for Jacobian evaluations to help in the accurate solution of process model. A genetic algorithms-based optimal control method is applied to realize the four optimal control objectives. The results show that optimal control can significantly enhance the performance of the batch polymerization process.     

Enantiomeric purity of (+/-) -methyl jasmonate in fresh leaf samples and commercial fragrances

The enantiomeric purity of (+/-) -methyl jasmonate in fresh leaf material of Jasminum from different species and Rosmarinus officinalis was examined by solid-phase microextraction-GC-MS (SPME-GC-MS). For comparison with these natural products, commercial jasmine and rosemary fragrances were also studied. The extraction conditions were selected as a result of testing different values of temperature (40, 50, and 60 degrees C) and time (2, 15, 30, and 40 min). The results obtained in this work revealed a range of enantiomeric excesses for (+/-) -methyl jasmonate varying from 13 to 95% depending on the Jasminum specie considered. In contrast, (-) -methyl jasmonate always occurred as a pure enantiomer in all R. officinalis samples studied. This implies those Jasminum species in which the enantiomeric purity of (-) -methyl jasmonate is high enough and any R. officinalis sample might be used as natural sources of pure (-) -methyl jasmonate. Concerning the commercial fragrances, those of jasmine showed enantiomeric composition of (-) -methyl jasmonate ranging from 1 to 15% whereas those of rosemary exhibited practically the pure (-) -methyl jasmonate. This fact suggests the addition and nonaddition of the racemic mixture of methyl jasmonate to the commercial jasmine and rosemary samples, respectively.     

Effect of solvent on reactions of Cp2Zr{(μ-H)2BHR}2 and Cp2ZrH{(μ-H)2BHR} (R = CH3, Ph) with B(C6F5)3

The effect that a solvent has on reactions of Cp₂Zr{(μ-H)₂BHR}₂ and Cp₂ZrH{(μ-H)₂BHR} (R = CH₃, Ph) with B(C₆F₅)₃ has been studied. From the reaction in benzene the metathesis product Cp₂Zr{(μ-H)₂B(C₆F₅)₂}₂, 2, was isolated. In the case of diethyl ether, different hydride abstraction products, including [Cp₂Zr(OEt₂){(μ-H)₂BHPh}][HB(C₆F₅)₃], 3, [Cp₂Zr(OEt₂){(μ-H)₂BHCH₃}][HB(C₆F₅)₃], 4, [Cp₂Zr(OEt₂){(μ-H)₂BH₂}][HB(C₆F₅)₃], 5, and [Cp₂Zr(OEt)(OEt₂)][HB(C₆F₅)₃], 6, were isolated depending on the starting zirconocene complex. The diethyl ether molecules of 3-6 are weakly coordinated to Zr and displaced in THF solution. Isolation of 3 and 4 is attributed to their fast precipitation from the reaction mixture, which prevented further reactions from occurring. In addition to the hydride abstraction, a hydride metathesis was also involved in the formation of 5. Time-elapsed ¹¹B NMR studies indicate that 3 and 4 are the intermediates on the pathway to 5 and 6. The molecular structures of 2-6 were determined by single-crystal X-ray diffraction.     

Stereoselective dioxirane hydroxylations and the synthesis of tripod boronic acid esters

Methyl(trifluoromethyl)dioxirane (TFDO, 1b), a powerful yet selective oxidant, was employed to achieve in high yield the direct stereoselective hydroxylation at tert-CH of cis,cis-1,3,5-trimethylcyclohexane (4), yielding triol 7 bearing all-axial disposition of the three OH groups. Similarly, TFDO oxidation of 1,3- and of 1,4-dimethylcyclohexane gave the corresponding Z-diols 5 and 6, respectively. Triol 7 was a convenient starting material to synthesize a novel borate—that is, 1-bora-2,8,9-trioxa-3,5,7-trimethyladamantane (8)—having a peculiar cage-shaped ‘tripod’ structure. From triol 7, novel tripod arylboronic Brönsted-assisted Lewis acids (BLA) could be obtained, as exemplified by 10a and 10b.     

δ-MnO2对TiO2光催化降解甲基橙的抑制作用

采用动力学方法研究了在水悬浮液中δ-MnO2颗粒物对P-25 TiO2光催化降解甲基橙活性的影响, 并利用紫外-可见漫反射光谱(DRS)和光致发光光谱(PL)对受δ-MnO2污染前后的TiO2样品进行了表征. 动力学研究结果表明, 在3种不同初始pH值条件下, δ-MnO2对TiO2光催化剂都具有明显的致毒效应, 共存δ-MnO2的浓度越大, 致毒效应越明显. 表征结果表明, 由于δ-MnO2 与TiO2之间的界面接触, 使得TiO2吸收带边蓝移, 紫外光区的吸收强度降低, 光致发光信号(PL)明显减弱. 因此, δ-MnO2导致TiO2的禁带宽度增大, 光利用率降低, 并且是光生电子与空穴的复合中心.     

Site specificity of alpha-H abstraction reaction among secondary structure motif--an ab initio study

The initial step of protein oxidation is studied through alpha-H abstraction by an OH radical with various secondary structure motifs of proteins. It is found that there exist preferential alpha-Hs in this kind of abstractions. The typical abstraction mechanism involves three steps: forming a pre-reactive complex before abstraction, the abstraction reaction, and the H(2)O detachment from a post-reactive complex to form the product, C(alpha)-center radical. Using the stability of the pre-reactive complex and the reaction barrier, we provide some explanation for this site preference. The feasibility of alpha-H abstraction by OH radical depends not only on the types of secondary structure, but also on the reaction condition, such as in aqueous or in gas phase. Moreover, the reactivity of the abstraction also depends on the location of alpha-H in the secondary structure motifs. The preferential alpha-Hs to be abstracted in beta-sheet are those immediate to the amide or carbonyl group, and without involving hydrogen bonding, whereas in reverse turns, the preferential alpha-Hs are near the C-terminal of type I and near the N-terminal of type II. In general, the alpha-Hs in alpha-helix are more difficult to be abstracted than those in beta-sheet and polypeptide in linear form. It is consistent with the trend of their bond dissociation energies. Our theoretical rate constant of N-acetyldiglycin-methylamide (Ac(Gly)(2)NHCH(3)) in aqueous solution (6.75 x 10(8) M(-1) s(-1)) is close to the experimental observation of N-acetyldiglycinamide (Ac(Gly)(2)NH(2)) (8.6 x 10(8) M(-1) s(-1)).     

有机钛催化草酸二甲酯与苯酚酯交换反应

研究了几种有机钛化合物对草酸二甲酯(DMO)与苯酚酯交换反应的催化性能,发现催化活性及选择性顺序依次为二氯二茂钛＞钛酸四苯酯＞钛酸丁酯＞乙酰丙酮氧钛＞钛酸乙酯＞钛酸异丙酯,表明二氯二茂钛是一种性能较好的酯交换催化剂。在n(Cp2TiCl2) = 0.001 mol、n (DMO) =0.3mol、n (Phenol) = 0.2mol、T=180癈、t=2h优化工艺条件下,苯酚转化率可达44.0%,甲基苯基草酸酯(MPO)和草酸二苯酯(DPO)收率分别达37.8%和6.1%,酯交换总选择性为99.8%。     

Preparation and properties of thermoexpandable polymeric microspheres

In this paper,thermoexpandable polymeric microspheres were prepared by suspension polymerization with acrylonitrile(AN) and methyl methacrylate(MMA) as monomers and i-butane as a blowing agent.The micromorphology and thermal stability were researched by polarized microscopy and TGA.The diameter of the expandable microspheres increased from about 20 mm(unexpanded) to 40–80 mm(expanded) upon heating.The maximum expansion volume was higher than 22 times of the original volume and the density of the expanded microspheres was about 16.7 kg/m3.The blowing agent content in microspheres was about 20 wt% and To.e.,Tm.e.and To.s.were 80 8C,120–130 8C and 140–145 8C,respectively.     

Physico-chemical studies on some saccharides in aqueous cellulose solutions at different temperatures – Acoustical and FTIR analysis

The ultrasonic velocity (u), density (ρ) and viscosity (η) of Fructose, Lactose and Sucrose in 0.4 M of Hydroxy Propyl Methyl Cellulose (HPMC) solutions have been investigated at 303, 313 and 323 K, respectively. The acoustical parameters such as adiabatic compressibility (β), intermolecular free length (L_f), internal pressure (π_i), Rao’s constant (R_a), relaxation time (τ), acoustical impedance (Z_a), absorption coefficient (α/f²), free volume (V_f), cohesive energy (CE) and solvation number (S_n) have been computed. The non linear variations of acoustical parameters with concentration and temperature indicated the existence of strong molecular interaction in the systems studied. The FTIR spectroscopic analysis revealed the possibility of intermolecular hydrogen bonding in various saccharides.     

CH Bond Activation with Triel Metals: Indium and Gallium Zwitterions through Internal Hydride Abstraction in Rigid Salan Ligands

The hydropyrimidine salan (salan=N,N′‐dimethyl‐N,N′‐bis[(2‐hydroxyphenyl)methylene]‐1,2‐diaminoethane) proteo‐ligands with a rigid backbone {ON^(CH₂)^NO}H₂ react with M(CH₂SiMe₃)₃ (M=Ga, In) to yield the zwitterions {ON^(CH⁺)^NO}M^?(CH₂SiMe₃)₂ (M=Ga, 2 ; In, 3 ) by abstraction of a hydride from the ligand backbone followed by elimination of dihydrogen. By contrast, with Al₂Me₆, the neutral‐at‐metal bimetallic complex [{ON^(CH₂)^NO}AlMe]₂ ( [1]₂ ) is obtained quantitatively. The formation of indium zwitterions is also observed with sterically more encumbered ligands containing o‐Me substituents on the phenolic rings, or an N (CHPh) N moiety in the heterocyclic core. Overall, the ease of C?H bond activation follows the order Al?Ga<In. Experimental data based on model complexes, XRD studies, and ²H NMR spectroscopy show that the formation of the Ga/In zwitterion involves rapid release of SiMe₄ followed by evolution of H₂, and suggest the formation of a transient metal‐hydride species. DFT calculations indicate that the systems {ON^(CH₂)^NO}H₂+M(CH₂SiMe₃)₃ (M=Al, Ga, In) all initially lead to the formation of the neutral monophenolate dihydrocarbyl species through a single protonolysis. From here, the thermodynamic product, the model neutral‐at‐metal complex 1 , is formed in the case of aluminum after a second protonolysis. On the other hand, lower activation energy pathways lead to the generation of zwitterionic complexes 2 and 3 in the cases of gallium and indium, and the formation of these zwitterions obeys a strict kinetic control; the computations suggest that, as inferred from the experimental data, the reaction proceeds through an instable metal‐hydride species, which could not be isolated synthetically.