Polymerization of methyl methacrylate under ultrasonic irradiation. Part V. Effect of ultrasonic irradiation on stereoregularity of the polymers and oligomers produced by grignard catalyst in toluene–dioxane mixed solvent

Polymerization of methyl methacrylate with Grignard reagent in toluene–dioxane mixed solvent was carried out under ultrasonic irradiation. The effects of ultrasonic irradiation and the order of catalyst addition on Grignard reagent and the microstructure in the reacting sites were examined on the basis of the stereoregularity of polymers and oligomers produced. The formation of oligomers was also discussed on the basis of the consumption of initiator. The stereoregularity of the polymers in series A (no ripening of catalyst with solvent) is higher than that in series B (ripening of catalyst with solvent). The effect of ultrasonic irradiation on the stereoregularity was completely reversed in series A and B; it increased in the former and decreased in the latter with ultrasonic irradiation. Similar results were obtained for the stereoregularity of the oligomers, but the stereoregularity of the oligomers was lower than that of polymers.     

The effects of ultrasonic irradiation on the preparation and properties of Ormosils

Organically modified silicates (Ormosils), derived from silica and polydimethylsiloxane (PDMS), have been prepared by the sol-gel method with ultrasonic irradiation. Tetraethoxysilane (TEOS), PDMS, water and HCl were mixed and exposed to 20 kHz ultrasonic waves under various conditions. Ultrasonic irradiation shortened the gelation time and made it possible to obtain gels without the addition of solvent (e.g. alcohol and tetrahydrofuran (THF)). The reaction mechanism of the ultrasonic irradiated Ormosil solution was investigated by liquid state ²⁹Si NMR. The densities of the gels prepared under ultrasonic irradiation were found to be much higher than those without irradiation. The effect of solvent addition on the properties of gels was also investigated.     

NMR studies on the stereospecific polymerization of methyl vinyl ether. Part II. Polymerization by sulfuric acid–aluminum sulfate complex: Enantiomorphic catalyst sites model

Highly crystalline poly(methyl vinyl ether) (PMVE) was produced in toluene in a temperature range of 0 to ?20°C. with the use of sulfuric acid–aluminum sulfate complex (SA catalyst). It was found from the NMR spectra that these polymers contained more than 50% of the triad isotactic fraction and the melting point of the unfractionated polymer was about 130°C. However, PMVE containing a large amount of the isotactic fraction was insoluble in nitromethane, so the triad tacticity of highly crystalline PMVE could not be quantitatively determined. The molecular weight of PMVE increased with increasing conversion and increasing polymerization temperature. This behavior is different from that in metal halide catalysts. Also, the stereoregularity of PMVE decreased with increasing monomer concentration. However, addition of a polar solvent and increasing the polymerization temperature had little effect on the stereoregularity of the polymer. The increase in the isotactic fraction at high catalyst concentration and the difference in the monomer composition in the copolymerization of methyl vinyl ether with 2-chloroethyl vinyl ether by SA catalyst from that obtained by BF₃·O(C₂H₅)₂ suggest that the absorption of MVE on a catalyst surface is an important step in the propagation step by SA catalyst. The fraction of the triad tacticity calculated from the enantiomorphic catalyst sites model⁸ coincided with the experimental results. This fact shows that the steric structure of the adding monomer is determined only by the nature of the catalyst irrespective of the nature of a growing chain end. It is concluded, on considering also the results of the previous paper, that completely different factors can control the steric structure of a polymer even for the same monomer when different catalysts are used.     

Preparation of Fe-doped mixed crystal TiO2 catalyst and investigation of its sonocatalytic activity during degradation of azo fuchsine under ultrasonic irradiation

In this work, Fe-doped mixed crystal TiO2 powder as sonocatalyst was prepared by the sol-gel method and heat treatment, and a novel method combined with ultrasonic irradiation was propounded to degrade the organic polluted water. First, the Fe-doped mixed crystal TiO2 powder was characterized by TG-DTA, XRD, and TEM techniques. Ultrasound was used as the irradiation source and the azo fuchsine was chose as the model compound. Then a series of degradation experiments was carried out in the presence of Fe-doped mixed crystal TiO2 powder. Also, the degradation process and some influencing factors, such as irradiation time, doping Fe3+ ion content, added amount of catalyst, and initial concentration of azo fuchsine solution, on the degradation were investigated by UV-vis spectra, ion chromatography, and HPLC. Through the degradation of azo fuchsine, it was found that the combination of ultrasonic irradiation and Fe-doped mixed crystal TiO2 powder can completely degrade the azo fuchsine in aqueous solution. Because of the good degradation efficiency, this method may be an advisable choice for the treatments of non- or low-transparent wastewaters in the future.     

Molecular structure development of metallocene‐catalyzed linear low density polyethylene under ultrasonic irradiation

In this work, the effect of ultrasonic irradiation on molecular structure development of metallocene‐catalyzed linear low density polyethylene (mLLDPE) was studied. GPC results show that ultrasonic irradiation have influence on molecular weight and molecular weight distribution of mLLDPE. Molecular weight of mLLDPE decreases slightly at the initial 30 s of ultrasonic irradiation and then increases obviously; its distribution becomes wider with the increase of ultrasonic irradiation time. The power and frequency of ultrasonic irradiation have the distinct influence on molecular weight and its distribution of mLLDPE. DSC results show that ultrasonic irradiation has distinct influence on multiple step crystallizing behaviors of mLLDPE because of the change of branched chain in mLLDPE molecules. Thermal stability of mLLDPE is improved greatly because of micro‐crosslinking structure in mLLDPE molecule, which is formed in the presence of ultrasonic irradiation. A possible mechanism for molecular structure development of mLLDPE in the presence of ultrasonic irradiation is also proposed in this paper. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2121–2129, 2005     

[Mn(salophen)Cl] supported on modified polystyrene as a selective heterogeneous catalyst for oxidation of sulfides under ultrasonic irradiation

The use of ultrasonic irradiation for the selective synthesis of sulfone in the oxidation of sulfides with NaIO₄ catalyzed by Mn(Salophen) supported on chloromethylated polystyrene-bound imidazole, [Mn(Salophene)-PSI], is reported. This heterogeneous catalyst efficiently catalyzed selective oxidation of sulfides to sulfones under ultrasonic irradiation and no sulfoxide was detected in the reaction mixture.     

Preparation of micron-sized aromatic polyamide particles using ultrasonic irradiation

Aromatic polyamide particles were prepared by reacting p-phthalyl chloride and 4,4′-diaminodiphenyl ether in an acetone solution with a high water content, using a precipitation polymerization method with ultrasonic irradiation. The average particle diameter was ca. 712 nm, and the particles were porous and spherical with a narrow size distribution. They showed a high degree of crystallinity and excellent thermal stability. The morphology and the thermal decomposition temperature of the submicron particles were found to depend strongly on the volume of water added to the reaction system. In this polymerization method, the addition of water was essential for the formation of spherical particles. The simultaneous mixing process resulted in the formation of particles with a narrow size distribution, and the use of ultrasonic irradiation was effective in reducing particle size.     

转晶纳米TiO2的制备及其声催化活性的研究

近几年兴起的半导体多相光催化技术在有机废水处理方面受到了人们的普遍关注[1,2]。众多的半导体光催化剂材料中,TiO2因其化学性质稳定和催化效率高而倍受青睐[3,4]。在紫外光的照射下,TiO2与H2O产生具有极强氧化能力的HO·自由基,最终可使废水中的有机物完全降解生成CO2,H2O以     

Multi-wall carbon nanotube supported manganese(III) porphyrin: an efficient and reusable catalyst for oxidation of 2-imidazolines with sodium periodate

The oxidation of 2-substituted imidazolines with sodium periodate catalyzed by tetrakis(p-aminophenyl)-porphyrinatomanganese(III) chloride, [Mn(TNH₂PP)Cl], supported on functionalized multi-wall carbon nanotubes is reported. A wide variety of 2-imidazolines were efficiently converted to their corresponding imidazoles by this catalytic system. When the same reaction was subjected to ultrasonic irradiation, the reaction times were reduced significantly and the product yields were increased. This catalyst could be reused several times without significant loss of activity. The effects of reaction parameters such catalyst amount, choice of solvent, and the effects of ultrasonic irradiation on the catalytic activity have been investigated.     

Stereospecific polymerization of α-methylstyrene by friedel-crafts catalysts

The relationship between stereoregularity and polymerization conditions of α-methylstyrene has been studied by means of NMR spectra. The effects of solvents and various Freidel-Crafts catalysts have been investigated. The stereoregularity of poly-α-methylstyrene increased with increased polymer solubility in the solvent used and with decreasing polymerization temperature. This behavior is completely different from the stereospecific polymerization of vinyl ethers and methyl methacrylate in homogeneous systems. This may be due to the strong steric repulsion exerted by the two substituents in the α-position of α-methylstyrene. For example, with BF₃ · O(C₂H₅)₂ as catalyst at ?78°C., atactic polymer is obtained in n-hexane, a nonsolvent for α-methylstyrene, whereas highly stereoregular polymer is produced in toluene or methylene chloride, good solvents for the polymer. However, the polarity of the solvent and the nature of the catalyst hardly affect the stereoregularity of the polymer.     

超声波-二氧化钛光催化耦合法降解高效氯氰菊酯

采用超声波-TiO2光催化耦合法降解高效氯氰菊酯,考察了高效氯氰菊酯初始浓度、降解时间、溶液pH、催化剂用量等对高效氯氰菊酯农药残留的降解效果,并利用水果进行了实物模拟.结果表明:利用超声波-TiO2光催化耦合法能够有效地降解高效氯氰菊酯农药残留.在弱酸环境中,当纳米TiO2投放量为1.2g/L时,经2h超声催化降解,不同浓度的高效氯氰菊酯农药稀释液均被有效降解,降解率最高可达98.3%.     

Oxidation-extraction spectrometry of reactive oxygen species (ROS) generated by chlorophyllin magnesium (Chl-Mg) under ultrasonic irradiation

In order to examine the mechanism and process of sonodynamic reaction, the chlorophyllin magnesium (Chl-Mg) acting as a sonosensitizer was irradiated by ultrasound, and the generation of reactive oxygen species (ROS) were detected by the method of oxidation-extraction spectrometry (OES). That is, under ultrasonic irradiation in the presence of Chl-Mg, the 1,5-diphenyl carbazide (DPCI) is oxidized by generated ROS into 1,5-diphenyl carbazone (DPCO), which can be extracted by mixed organic solvent and display a obvious visible absorption at 563 nm wavelength. Besides, the generation conditions of ROS were also reviewed. The results demonstrated that the quantities of generated ROS increased with the increase of ultrasonic irradiation time, Chl-Mg concentration and DPCI concentration. Finally, several radical scavengers (l-Histidine (His), 2,6-Di-tert-butyl-methylphenol (BHT) and Vitamin C (VC)) were used to determine the kind of the generated ROS. It was found that at least the hydroxyl radical (OH) and singlet oxygen (1O2) were generated in the presence of Chl-Mg under ultrasonic irradiation. It is wish that this paper might offer some valuable references for the study on the mechanism of SDT and the application of Chl-Mg in tumor treatment.     

[Mn(TPPS)] immobilized on ionic liquid-modified silica as a heterogeneous and reusable catalyst for epoxidation of alkenes with NaIO<Subscript>4</Subscript> under ultrasonic irradiation

Effective epoxidation of alkenes using sodium periodate was accomplished with Manganese (III) tetrakis(p-sulfonatophenyl)porphyrin, [C₄₄H₂₆N₄O₁₂S₄Na₄], supported on ionic liquids-modified silica, Im-SiO₂, under ultrasonic irradiation conditions is reported. This heterogeneous catalyst, [Mn(TPPS)@SiO₂-Im] was characterized by elemental analysis, scanning electron microscopy (SEM), FT-IR and UV–Vis spectroscopic methods. The synthesized hybrid catalyst was applied for efficient epoxidation of various alkenes with sodium periodate in acetonitrile under ultrasonic irradiation conditions. This solid catalyst can be easily recovered by simple filtration and reused several time without apparent loss of its catalytic activity.     

Molten salt ionic liquid-assisted synthesis of nano-structured poly(amide imide)s based on 4,4′-methylenebis(3-chloro-2,6-diethyl trimellit imidobenzene) via microwave process as an environmentally friendly methodology

In this paper, for the first time, 4,4′-methylene-bis(3-chloro-2,6-diethyl trimellit imidobenzene) was prepared by the condensation reaction of 4,4′-methylene-bis(3-chloro-2,6-diethylaniline) and trimellitic anhydride. A series of novel poly(amide imide)s was prepared by the direct polycondensation of the synthesized diimide diacid and various commercial diamines using tetra-n-butylammonium bromide and triphenyl phosphite as a condensing agent under microwave irradiation. Tetra-n-butylammonium bromide acts both as a solvent and a catalyst to mediate clean polymerization reactions to yield the desired polymers. The obtained polymers were characterized with FTIR, ¹H NMR, X-ray diffraction, field emission scanning electron microscopy, elemental and thermogravimetric analysis. The poly(amide imide)s were generally soluble in polar organic solvents, such as N,N′-dimethyl acetamide, N,N′-dimethylformamide, N-methyl-2-pyrrolidone and sulfuric acid at room temperature, and are insoluble in methylene chloride, cyclohexane and water. Morphology probes showed these macromolecules were non-crystalline and nano-structured polymers. The effect of ultrasonic irradiation on the surface morphology of polymers was studied and the results demonstrated that the morphology of macromolecules after ultrasonication became more homogenous than it is before ultrasonic radiation. On the basis of thermogravimetric analysis data, such polymers are thermally stable and can be classified as self-extinguishing polymers.     

Borylation of calix[4]resorcinols under ultrasonic irradiation

The use of ultrasonic irradiation in the reactions of trialkyl borates with octahydroxytetraoctyl[l ₄] metacyclophane allowed us obtaining tetraalkoxyboratocavitands with higher yields and under milder conditions. We first obtained 1,3,2-dioxaborolane and 1,3,2-dioxaborinane derivatives of tetraoctyl[l ₄]metacyclophane using ultrasonic irradiation. Boratocavitands were converted into the corresponding amine complexes with isobutylamine.     

Micowave assisted synthesis of benzo‐substituted macrocyclic diamides and their corresponding macrocyclic dithiodiamides

A synthesis of a series of macrocyclic diamides 3 in good yields by reacting the corresponding bis phenols 4 with the appropriate dihalo alkanes 6 either in solvent or in dry media under microwave irradiation. Thiation of 3 with P₂S₅ or Lawesson's reagent in solvent free conditions under microwave irradiation is also described.     

One-pot synthesis of 2,5-disubstituted-1,3,4-thiadiazoles under ultrasonic irradiation

A facile one-pot synthesis of 2,5-disubstituted-1,3,4-thiadiazoles was achieved by ultrasonic irradiation of a mixture of 1- naphthylacetyl chloride,NH_4CNS,CH_2Cl_2 and PEG-400 for 1.5 h at 10-20℃and subsequent irradiation for 1.5h in the presence of N-arylglycine hydrazides.This method requires short time and gives thiadiazoles in high yields.     

Polymerization of 4-phenyl-1-butyne catalyzed by metathesis and Ziegler–Natta catalysts

The polymerization of 4-phenyl-1-butyne was carried out using metathesis and Ziegler-Natta catalysts. Especially, the Fe(acac)₃-AlEt₃ catalyst with toluene as a solvent produced an extremely high molecular weight polymer of M_w ≈ 10⁶. Solubility of the polymers at room temperature in organic solvents such as benzene, toluene, dichloromethane, chloroform, and THF was excellent despite their high molecular weights. It has been indicated that the polymer prepared by the Fe(acac)₃-AlEt₃ catalyst is of cis form with a high stereoregularity. © 1993 John Wiley & Sons, Inc.     

Iron-catalyzed cross-coupling of aryltrimethylammonium triflates and alkyl Grignard reagents

Fe(acac)₃ effectively catalyzes reaction of aryltrimethylammonium triflates with β-hydrogen-containing primary or secondary alkyl Grignard reagents in a mixed solvent of THF and NMP at room temperature. A series of functional groups are tolerated under the reaction conditions.     

Synthesis of polystyenes with different stereoregularities by anionic polymerization

The stereoregularity of polystyrene prepared by anionic polymerization was determined by means of ¹³C-NMR spectroscopy. The stereoregularity changed with such polymerization conditions as catalyst, solvent, and temperature. Sodium naphthalene as catalyst gave a syndiotactic-rich polystyrene of 66–68% syndiotactic dyads independently of solvent and temperature, while potassium and cesium naphthalenes as catalyst produced polystyrenes with different stereoregularities ranging from syndiotactic-rich to isotactic-rich configurations, depending on solvent and temperature. The mechanism of anionic polymerization which caused the difference in stereoregularity was discussed from the viewpoint of growing ionic species.