Graft copolymers having hydrophobic backbone and hydrophilic branches. III. Synthesis of graft copolymers having oligovinylpyrrolidone as hydrophilic branch

Graft copolymers were synthesized by the esterification reaction between acrylic copolymers and carboxyl group terminated vinylpyrrolidone oligomer using phase transfer catalysts. Acrylic copolymers were obtained by the radical copolymerization of β-bromoethyl methacrylate, chloromethylstyrene or glycidyl methacrylate with methyl methacrylate. Hydrophilic oligomers were prepared by the radical oligomerization of vinylpyrrolidone using β-mercaptopropionic acid as chain transfer agent. The degree of esterification increased with decreasing the molecular weight of oligomer and with increasing the number of potential grafting sites on polymer backbones. The water dispersibility of graft copolymers increased with increasing the nitrogen content and was therefore dependent on the branch oligomer content.     

Oligomerization of Substituted Phenyl Glycidyl Ethers with Tertiary Amine

The oligomerization of substituted phenyl glycidyl ethers was studied kinetically in the presence of dimethylbenzylamine using toluene or dioxane as a solvent. The infrared spectra of the resultant oligomers suggest that the reaction products have the internal carbon-carbon double-bond un-saturation, which is confirmed by the catalytic hydrogenation. The molecular weights of the oligomers also suggest that γ-phenoxy allyl alcohol produced by the initial reaction step, in which the γ-proton of phenyl glycidyl ether is attracted by a base, amine, reacts with other phenyl glycidyl ether and thus proceeds further, yielding the oligomer. The value of the reaction constant ρ is obtained positive for this reaction, which indicates that electron-withdrawing substituents of phenyl gylcidyl ethers increase the rate of oligomerization. A kinetic analysis shows that the proposed reaction sequence accounts for all the characteristics of the polymerization including sigmoidal shapes of monomer consumption curves, reaction rates, and induction periods.     

Insitu dehydro-oligomerization of castor oil,fatty acid ester into esters of dimer and oligomer acids over molybdenum oxide on silica-alumina catalyst

A process is described for the conversion of methylricinoleate, the major castor oil, fatty acid ester, directly into esters of dimer and oligomer acids by using molybdenum oxide on a silica–alumina catalyst. The dehydration of the methylricinoleate into a corresponding mixture of conjugated and nonconjugated olefins and the oligomerization reaction took place side by side in a continuous column, fixed-bed reactor. The products are characterized by IR, ¹H NMR, and MS. The fragmentation pattern in the mass spectrum of the dimeric species distilled from the mixture reveals that the product contains cyclic and acyclic isomeric structures. The mechanism of dimerization and oligomerization reactions to transition metal complexes and transition metal oxide catalyst systems is reviewed briefly and the possibility of a common mechanism for all similar systems is suggested. A general mechanism for oligomerization reactions to similar catalysts is proposed and the products of the present reaction are explained on the basis of the proposed mechanism.     

High-molecular-weight copolyesters of dihydroxybenzophenones by ‘induced‘ copolyesterification using TsCl/DMF/Py as a condensing agent

Dihydroxybenzophenones and 4,4′-dihydroxydiphenylsulfone, which yield high-molecular-weight polyesters only difficultly by conventional methods, gave high-molecular-weight copolyesters through a two-stage copolycondensation involving initial induction of oligomerization with selected monomers followed by copolycondensation. The copolycondensation was studied by examining such factors as the kinds of initial monomers, their amounts, initial reaction times, and the order of reaction, and the results are explained in terms of oligomer distribution in the initial oligomerization as determined by GPC. Copolycondensation was also facilitated by lowering the temperature at the second stage of reaction. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3625–3631, 1999     

Electroinitiated oligomerization of methyl acrylate in methanol solution

The electroinitiated oligomerization of methyl acrylate in methanol solution in the presence of lithium acetate was studied. It was found that in this system the initiator is the methyl radical (obtained from anodic oxidation of acetate ion), and the major termination step is the abstraction of hydrogen radical from methanol by the growing oligomer chain. Eleven compounds were found to be formed in the reaction. A reaction sequence for their formation together with an electric balance for the reactions is given.     

Kaminsky型催化剂催化乙烯环齐聚反应的研究

研究发现Cp~2ZrL~2(L=Cl,Me,OC~6H~4-p-Me)/EAO(乙基铝氧烷)可同步催化乙烯齐聚-环化反应,不仅给出链状烯烃,而且生成环状剂聚物－－亚甲基环戊烷。环状齐聚物的选择性取决于主催化剂的结构和浓度,反应介质,预反应温度和反应温度,反应时间,Al/Zr比及烷基铝水解程度等因素,加入碱性第三组分对催化活性和选择性亦有一定影响。在优化反应条件下,亚甲基环戊烷的选择性达到37%。     

Thermal oligomerization of isophthalonitrile catalyzed by o-carborane

The thermal reaction of equimolar quantities of isophthalonitrile and o-carborane has been shown to produce an adduct oligomer of isophthalonitrile. The structure was determined to involve condensation of three to five isophthalonitrile molecules to form a triazine-type system. This type of bonding gave rise to a trimer and pentamer. Further, the reaction was a homogeneous liquid phase reaction in which o-carborane is involved in a catalytic manner in the oligomerization. The overall reaction has first-order kinetics with an activation energy of 32.2 kcal/mole.     

一种后过渡金属催化剂催化乙烯低聚动力学研究

设计并合成了一种新型的后过渡金属铁络合物 { [(2 ArNC(Me) ) 2 C5H3N]FeCl2 } (Ar =2 ,4 C6 H4(CH3) 2 ) ,研究了该络合物 甲基铝氧烷 (MAO)催化乙烯低聚 ,讨论了低聚反应温度、Al Fe摩尔比、催化剂浓度、反应压力等对催化剂活性及反应速率的影响 .本催化剂的最大特点是活性高 (在 30℃ ,3 0MPa时活性可达 4 2 6× 10 8goligomer·molFe·h- 1 )、初速度大 ,动力学曲线为衰减型 .     

Study of polymerization kinetics of acrylic and methacrylic acid esters at low conversions

The kinetics of high-energy radiation initiated polymerization of acrylate and methacrylate monomers were studied in dilute cyclohexane solutions. The absorption spectra of the intermediates were obtained by pulse radiolysis with optical detection. In solutions of acrylates at longer times after the pulse the presence of oligomer radicals was observed. In solutions of methacrylates the beginning of the oligomerization reaction was detected at higher monomer concentrations. From the kinetic curves the rate coefficients of termination were calculated.     

1－丁烯齐聚反应 X．羧酸镍／有机铝体系催化性能的调变

１－丁烯齐聚反应　Ｘ．羧酸镍／有机铝体系催化性能的调变高占先，李文忠，林青松，周科衍（大连理工大学化工学院，大连１１６０１２）关键词Ｚｉｅｇｌｅｒ催化剂，丁烯齐聚，卤代乙酸镍，有机铝，催化性能调变在［（η３Ｃ３Ｈ５）ＮｉＸ］２／ＡｌＥｔ１．５Ｃｌ１．...     

Oligomers of stereoregular polymers

The embryonic state of the ionic methyl methacrylate (MMA) and of trihaloacetaldehyde polymerization was studied. The composition of the oligomer mixtures, the end groups and the stereochemistry of individual compounds of the oligomers was investigated. Depending upon the initiating systems the oligomerization of methyl methacrylate can give either isotactic or syndiotactic oligomers. Trihaloacetaldehye oligomerization is highly dependent on the ceiling temperature of polymerization. The oligomerization of fluoral and chloral is compared with a more detailed study of the bromal polymerization and even more interestingly with the cooligomerization of chloral and bromal.     

Mechanism of oligomerization reactions of silica

The mechanism of the oligomerization reaction of silica, the initial step of silica formation, has been studied by quantum chemical techniques. The solvent effect is included by using the COSMO model. The formation of various oligomers (from dimer to tetramer) was investigated. The calculations show that the anionic pathway is kinetically preferred over the neutral route. The first step in the anionic mechanism is the formation of the SiO-Si linkage between the reactants to form a five-coordinated silicon complex, which is an essential intermediate in the condensation reaction. The rate-limiting step is water removal leading to the oligomer product. The activation energies for dimer and trimer formation ( approximately 80 kJ/mol) are significantly higher than those of the subsequent oligermerization. The activation energies for the ring closure reaction ( approximately 100 kJ/mol) are even higher. The differences in activation energies can be related to the details in intra- and intermolecular hydrogen bonding of the oligomeric complexes.     

Study of high-energy radiation initiated polymerization of butyl acrylate

The kinetics and mechanism of the first steps of radiation initiated polymerization was studied in cyclohexane solution of butyl acrylate applying pulse radiolysis with optical detection. By increasing the monomer concentration, the shape and wavelength of the maximum of the spectrum was changed indicating the start of the oligomerization reaction. From the kinetic curves average rate coefficients of termination for the oligomer radicals (2k_t) were determined. They were found to decrease in time (that is with increasing chain-length).     

Computational study on the structural diversity of amyloid Beta Peptide (abeta(10-35)) oligomers

We studied the oligomerization of Alzheimer amyloid beta peptide (Abeta) using a replica exchange molecular dynamics (REMD) simulation. The simulation was performed with Abeta(10-35) dimers, trimers, and tetramers. Extensive REMD simulations illustrated several possible oligomer conformations. As the size of the oligomer increased from a dimer to a tetramer, the number of possible configurations was reduced. We identified all the possible conformations for each oligomer and characterized their temperature dependence. It was found that the detailed structures of the oligomers, which may act as folding intermediates, are highly sensitive to the parameters of the simulation environment such as temperature and concentration. Structural diversities of Abeta oligomers suggest multiple pathways of the aggregation process.     

Catalytic activity of a half-sandwich Ru(II)-N-heterocyclic carbene complex in the oligomerization of alkynes

The ruthenium(II)-N-heterocyclic carbene complex, [RuCl₂(1-butyl-3-methylimidazol-2-ylidene)(p-cymene)] selectively catalyzes oligomerization of phenylacetylene (PA) and its derivatives to linear oligomers, containing positively charged imidazolium end-group and uncharged ones. The charged oligomer chain consists of maximum 9-11 PA monomer units after 36 h reaction at 80 °C whereas mainly pentamers are formed as other products. The H₂ atmosphere retards oligomerization of PA and hydrogenation to vinylbenzene and ethylbenzene is observed instead.     

1,5,9-环十二碳三烯的阳离子型跨环齐聚合反应

本文研究1,5,9-环十二碳三烯在阳离子型引发剂AlCl3和BF3.OEt2催化下进行的跨环聚合反应, 考察各种反应条件对跨环聚合反应的影响, 产物为白色粉末, 分子量均在1096-1431之间对其溶解性, 核磁共振和红外光谱的分析, 确认了它的结构。     

Chromatographic Separations of Oligovinylpyridines. II. HPLC Separations of Radically and Anionically Oligomerized 2- and 4-Vinylpyridines

Abstract

HPLC-separations of oligomers obtained by radical and anionic oligomerization of 2- and 4-vinylpyridine by means of gradient elution are reported. The eluent systems used were pentane/methanol and nitrous oxide/methanol. Elution is shown to occur more rapidly with 2-vinylpyridine oligomers. Using nitrous oxide/methanol, separation with respect to degree of oligomerization was enhanced compared to pentane/methanol. Differences in the elution behavior of 2- and 4-vinylpyridine oligomers are ascribed to differences in interactions of the respective oligomer molecules with the stationary and the mobile phase, caused by the different position of the nitrogen atom in these two oligomer types.     

Surface modified microarray chip and laser induced fluorescence microscopy to detect DNA cleavage

This work describes a quantitative method to detect DNA damage in the presence of Pb and Cd ions using a surface modified microarray chip and a laser induced fluorescence microscopy (LIFM). The detection was carried out by the immobilization of a single-stranded DNA oligomer, tagged with a Cy5 fluorophore on a polydimethylsiloxane (PDMS) microarray chip followed by LIFM. Sulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxylate (Sulfo-SMCC) was attached as a cross-linker via the formation of covalent amide bonds. Then, the single-stranded DNA oligomer containing Cy5 as a fluorophore and thiol functional groups at both terminals, was bonded to the linker by reaction with sulfhydryl group. As the DNA oligomers were reacted with metal ions of Pb and Cd, the un-cleaved DNA oligomers were quantitatively identified by monitoring Cy5 fluorescence. Cadmium showed a quenching constant of 0.84 in the Stern–Volmer plot, whereas lead gave 0.22, indicating that cadmium ions suppress fluorescence more than lead ions. When optimized, fluorescence reductions of 23% (± 2.1) for Pb and 25% (± 1.4) for Cd were observed in air and decreased to almost < 5.0% in a radical scavenger of 5 mM. The cleaved DNA was also confirmed by MALDI-TOF-MS. In result, this experimental method using a microarray chip with surface modification provided quantitative determination of DNA oligomer damage with reproducible results, significantly reduced sample volumes and analysis times.     

Anionic syntheses of terminally functionalized ethylene oligomers

Synthetic procedures for preparation of terminally functionalized linear ethylene oligomers are described. The preferred synthetic method is anionic oligomerization of ethylene with n-butyllithium–tetramethylethylenediamine and electrophilic substitution of the living oligomer so-formed. Conditions and procedures for subsequent chemistry to elaborate the end groups of these oligomers are described. These procedures afford strictly linear ethylene oligomers which contain a wide variety of end groups and which range in molecular weight from 1000 to 4500 (M_n). The product oligomers were characterized spectroscopically as toluene-d₈ solutions at 110°C using multinuclear NMR, FT-IR, fluorescence, and UV-visible spectroscopies as appropriate. Alternative stepwise approaches to such oligomers are also discussed.     

Oligomerization of ethylene in the presence of heterogenized complex catalytic systems based on ionic liquid‐type substituted zirconium phenolates

The oligomerization of ethylene was investigated in the presence of novel catalytic systems consisting of alkylaluminium chlorides and heterogenized zirconium phenolates containing amino and imino hydrochloride substituents. It was determined that the composition of a synthesized oligomer and the activity or selectivity of the catalyst systems depend on various parameters such as the molar ratio of Zr:Al, the composition of alkylaluminium, the temperature of the reaction, the pressure of ethylene and the structure of zirconium phenolates. The results showed that C₄‐C₁₀ linear α‐olefins were obtained with high selectivity when diethylaluminium chloride was used as a co‐catalyst. The process of the separation of a synthesized oligomer from the catalyst containing amino and imino hydrochloride ionic liquid substituents was carried out by simple decantation, and after this process zirconium complexes could be reused several times for successive ethylene oligomerizations.