Synthesis of Syndiotactic Polystyrene with Novel Titanocene Catalysts Activated by Modified Methylaluminoxane

Thesynthesisofsyndiotacticpolystyrene(sPS)hasattractedmuchinterestforitspropertiesandapplications.Half-sandwichtitanoceneandmethylaluminoxane(MAO)catalystshavebeenfoundtobethefavourprecursorstocatalyzesyndiospecificpolymerizationofstyrene'-,'.MAOascocatalystsalwayscontainssomeamountoffreetrimethylaluminum(TMA)bothinaformcoordinatedtoMAOandasfreeTMA".However,therolesoftheTMAcoexistinginMAOarestillnuclear.Inthispaper,severalmodifiedmethylaluminoxanes(m-MAO)whichcontaineddifferentpercen…     

Highly Efficient Transition Metal Nanoparticle Catalysts in Aqueous Solutions

A ligand design is proposed for transition metal nanoparticle (TMNP) catalysts in aqueous solution. Thus, a tris(triazolyl)‐polyethylene glycol (tris‐trz‐PEG) amphiphilic ligand, 2 , is used for the synthesis of very small TMNPs with Fe, Co, Ni, Cu, Ru, Pd, Ag, Pt, and Au. These TMNP‐ 2 catalysts were evaluated and compared for the model 4‐nitrophenol reduction, and proved to be extremely efficient. High catalytic efficiencies involving the use of only a few ppm metal of PdNPs, RuNPs, and CuNPs were also exemplified in Suzuki–Miyaura, transfer hydrogenation, and click reactions, respectively.     

FTIR spectra and structure of new polystyrenes: Syndiotactic polystyrene and poly-para-methyl-styrene

Highly syndiotactic poly(styrene) shows higher crystallinity and a higher melting point than the corresponding isotactic material. Temperature dependent FTIR spectra have been recorded and the structural evolution of the system from the ordered to the amorphous phase has been followed.     

Synthesis and Conformation of Three‐Dimensionally Ordered Macroporous Syndiotactic Polystyrene and Poly(p‐methyl styrene)

Three‐dimensionally ordered macroporous (3DOM) syndiotactic polystyrene (sPS) and poly(p‐methyl styrene) (sPPMS) are synthesized using silica colloidal crystal templates with varied diameters in the range of 548–214 nm, and the effect of polymerization space on the conformation of the resulting 3DOM polymers is investigated by spectroscopy and thermal analysis. In‐situ polymerizations of styrene and p‐methyl styrene within the silica templates induce the resulting 3DOM polymers with different conformations and packing of chains, which are different from those of bulk polymers prepared in the absence of templates. Polymerizations in restricted silica templates result in un‐helixication of 3DOM sPS chains and helixication of 3DOM sPPMS chains.

     

取代芳基钛酸酯类化合物催化苯乙烯间规聚合

以取代芳基钛酸酯化合物为催化剂催化苯乙烯聚合,考察了催化剂、聚合温度,摩尔比nAl/nTi以及聚合时间等因素对聚合行为及产物性质的影响。并用13C-NMR、FT-IR、DSC等手段表征了聚合产物。结果表明:在nAl/nTi=1 000,聚合温度为60℃条件下,2,2′-硫代双(4-甲基-6-叔丁基酚氧基)二氯化钛催化苯乙烯聚合显示出很高的催化活性,其活性为6.87×105g sPS/(mol Ti.h),所得聚合物为间规聚苯乙烯,间规度96.9%,分子量为1.98×105。     

Multiple Melting Endotherms of Syndiotactic Polystyrene in β Crystalline Form

Multiple melting behaviors have been studied extensively. Syndiotactic polyStyrene(SPS), in 6 crystalline form exhibited such phenomena. It was suggested that arecrystallization process occurred since it has been clarified that no other modificationswere observed during the DSC heating scanl. In this study, a series of SPS samples in 0form were prepared by cooling from the melt at various cooling ratesl and the factors thatinfluence the multiple melting behavior of SPS in 0 form were exam…     

Syndiotactic Polystyrene / Fullerene Composites: Elucidation of Structural Aspect

Summary: Syndiotactic polystyrene (sPS), an attractive polymer due to its wide range of application, forms polymer-solvent intercalates with a large variety of solvent molecules ranging from liquids to solids. Recently, it has been realized that sPS intercalate prepared from SPS/naphthalene gel is more promising of making mesoporous materials. Here, the composite of sPS/fullerene have been prepared by taking advantage of sublimation of naphthalene. The different techniques as like XRD, SEM, HRTEM, FT-IR, DSC, TGA etc have been employed to characterized sPS/fullerene composite. XRD investigation shows the presence of δ form sPS in the composite. SEM and HRTEM reveal the fibrillar network with fringe like structure in presence of fullerene only and the average diameter of fibril has increased as compared to pure sPS fibrils. The conductivities of these fibrils have been increased with increasing amount of fullerene.     

O-(4-喹唑啉)羟肟酸硫代酯(酰胺)类化合物的合成及生物活性

用差示扫描量热分析研究了间规聚苯乙烯（ｓＰＳ）的非等温结晶及其动力学，并分别用Ｏｚａｗａ和Ｊｅｚｉｏｒｎｙ两种方法来处理ｓＰＳ的非等温结晶数据．结果表明，在２５～４０℃／ｍｉｎ的冷却速率范围内，ｓＰＳ的半结晶时间随冷却速率增大而呈指数式下降，ｓＰＳ非等温结晶过程遵循Ｏｚａｗａ动力学方程，但不符合Ｊｅｚｉｏｒｎｙ方法中的Ａｖｒａｍｉ动力学方程．所得到的ｓＰＳ非等温结晶Ａｖｒａｍｉ指数ｎ在３６～４１之间，高于等温结晶时的ｎ值     

Orientation of Syndiotactic Polystyrene Crystallized in Cylindrical Nanopores

Syndiotactic polystyrene (sPS) nanorods with different diameters have been prepared by using anodic aluminum oxide templates, and the orientation of the sPS crystals in the nanorods has been investigated by FT‐IR spectroscopy. It is found that the c axis of the β′ crystals preferentially oriented perpendicular to the axis of the nanorod, and the degree of orientation is lower as the diameter of the nanorod decreases. This unexpected result is attributed to nuclei formed at the surface of the nanopores and their subsequent growth, in addition to the preferential growth compatible with the pore direction by the nuclei formed in the bulk film and in the nanorods.

     

弹性散射法研究间规聚苯乙烯的冷结晶行为

用弹性光散射方法研究了间规聚苯乙烯(s-PS)的非等温冷结晶行为和等温结晶动力学.结果表明,弹性散射信号对s-PS的冷结晶过程中的构象变化非常敏感.弹性散射法所得的大分子链玻璃化转变温度Tg以及冷结晶温度Tc与DSC的测量结果一致.此外,通过散射强度随温度的变化可以更为清晰地分辨出冷结晶过程中各个阶段,包括晶体成核期,晶核生长期以及二次结晶期.通过等温弹性散射测试,同时结合Arrhenius方程,计算得到s-PS冷结晶表观活化能Ea为309 kJ/mol.     

Three‐Dimensionally Ordered Macroporous Syndiotactic Polystyrene: Preparation and Characterization

Summary: Three‐dimensionally ordered macroporous (3DOM) syndiotactic polystyrenes with pore size in the range of 71–286 nm were fabricated by means of silica templates using (dbm)₂Ti(OPh)₂/MAO catalytic system. The resulting materials were characterized by NMR, SEM, powder X‐ray diffraction, GPC and DSC. The results indicated that the 3DOM syndiotactic polystyrenes were highly syndiotactic, and the pore contraction increased when the average pore diameter decreased. Compared with bulk syndiotactic polystyrenes, 3DOM syndiotactic polystyrene possessed lower molecular weight, narrower molecular weight distribution, and lower crystallinity and melting temperature.

SEM image of 3DOM syndiotactic polystyrene, the inset shows the detail of the cavities.     

Electrodynamics of Noble Metal Nanoparticles and Nanoparticle Clusters

In this paper we examine the electrodynamics of silver nanoparticles and of clusters of nanoparticles, with an emphasis on extinction spectra and of electric fields near the particle surfaces that are important in determining surface-enhanced Raman (SER) intensities. The particles and clusters are chosen to be representative of what has been studied in recent work on colloids and with lithographically prepared particles. These include spheres, spheroids, truncated tetrahedrons, and clusters of two or three of these particles, with sizes that are too large to be described with simple electrostatic approximations but small compared to the wavelength of light. The electrodynamics calculations are mostly based on the discrete dipole approximation (DDA), which is a coupled-finite element approach which produces exact or nearly exact results for particles of arbitrary size and shape if fully converged. Mie theory results are used to study the validity of the DDA for spherical particles, and we also study the validity of the modified long wavelength approximation (MLWA), which is based on perturbative corrections to the electrostatic limit, and of the single dipole per particle approximation (SDA). The results show how the dipole plasmon resonance properties and the electric field contours around the particle vary with particle shape and size for isolated particles. For clusters of particles, we study the effect of interparticle spacing on plasmon resonance characteristics. We also show that the quadrupole resonance is much less sensitive to particle shape and interparticle interactions than the dipole plasmon resonance. These results provide benchmarks that will be used in future comparisons with experiment.     

间规聚苯乙烯的多晶型和结晶行为概述

综述间规聚苯乙烯四种稳定的晶型（α、β、δ和γ）结构特点及各种晶型的制备方法。详述间规聚苯乙烯结晶和熔融行为等方面的研究进展。     

苯乙烯间规聚合催化剂进展

综述了苯乙烯间规聚合主催化剂的研究和开发状况。主要介绍茂、茚、多元稠合环，氟和非茂钛等较高活性催化剂的催化特性，从取代基的电子效应和空间效应以及活性种稳定性等方面阐述了不同催化剂的聚合活性差异。     

Comparison of Syndiotactic Polystyrene Morphology Obtained Via Heterogeneous and Homogeneous Polymerization with Metallocene Catalyst

Summary: Supported catalyst system for the slurry phase polymerization of styrene in toluene was prepared by the immobilization of 2-methylindenyltrichlorotitanium(2-MeIndTiCl₃) on silica and activation of this catalyst was performed by methylaluminoxane(MAO) in polymerization media. Homogeneous polymerization of styrene with 2-methylindenyltrichlorotitanium activated by MAO was performed in toluene. The morphology of obtained syndiotactic polystyrene (sPS) via heterogeneous and homhgeneous catalyst system was compared. Polymerization of styrene by homogeneous catalyst lead to formation of gel and resultant polymers presented a compact and dense texture while the global gelation do not occur with silica supported catalyst at different Ti/SiO₂ mol ratios and sPS was obtained as separated particles. Unlike to the homogeneous catalyst, obtained polymers showed a porous texture. Highly porous texture of sPS was obtained with Ti/SiO₂ = 0.5% mol ratio.     

用广角X光衍射测定不同晶型间规聚苯乙烯结晶度

多晶型;用广角X光衍射测定不同晶型间规聚苯乙烯结晶度     

ZrCl4(THF)2/Methylaluminoxane as the Catalyst for the Syndiotactic Polymerization of Styrene

The presence of an organic Lewis base, such as THF, enhances the syndiospecificity of the catalytic system ZrCl₄/methylaluminoxane toward the polymerization of styrene. The polymer has low molecular weight and a microstructure similar to other polystyrenes obtained with zirconium‐based catalysts.     

Complexation of Syndiotactic Polystyrene with 12‐Crown‐4

Solid‐state complexation of syndiotactic polystyrene (sPS) with a crown ether compound, 1,4,7,10‐tetraoxa‐cyclododecane (12‐crown‐4), took place when a film of sPS/chloroform clathrate was subjected to a guest exchange procedure assisted with a plasticizing agent. The new guest 12‐crown‐4 molecules were incorporated into the crystalline region of the sPS film, without causing a large conformational change of host sPS helices. X‐ray diffraction and thermogravimetric investigations showed that sPS/12‐crown‐4 complex had a clathrate complex structure which contained four 12‐crown‐4 molecules per unit cell. IR and Raman data suggested that 12‐crown‐4 took a C_i‐type conformation in the sPS complex phase.