Synthesis of Star-Shaped Polystyrenes with Glucose in the Chain-End and Core

2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) was reacted with 4-ethylphenyl 2,3,4,6-tetra-O-acetyl-β-D -glucopyranoside using tert-butyl hydroperoxide and cobalt(II)acetate tetrahydrate in acetonitrile. The reaction provided 4-[1′-(2″,2″,6″,6″-tetramethyl-1″-piperidinyloxy)-ethyl]phenyl 2,3,4,6-tetra-O-acetyl-β-D -glucopyranoside, glycoconjugated initiator. Star-shaped polystyrene architectures in which glucose was covalently bonded in the core and chain-end were successfully prepared from the glycoconjugated initiator, styrene, and 1,4-divinylbenzene as starting materials.     

端羟基化聚苯乙烯的表面性质

利用Wilhelmy片技术和躺滴法研究了端羟基化聚苯乙烯的表面性质.结果表明,端羟基化对聚苯乙烯在空气面的接触角基本没有影响(89°),而在玻璃面的接触角则大大降低(66°),其降低幅度与分子量及分子量分布有关.这与动态接触角的测定结果基本一致,而且宽分子量分布的端羟基化聚苯乙烯的前进接触角(θa)随着温度的升高而降低,于40℃时达到最低值.而窄分子量分布样品的动态接触角基本不变.样品与不同温度水接触后表面接触角的变化也基本相似.DMA研究结果表明,样品损耗模量、储能模量和tanδ从40℃开始发生突变,刚好与接触角最低值的温度相对应.这是由于宽分子量分布样品中的较低分子量组分在表面聚集,导致表面分子具有较高的活动能力.接触角随温度的变化趋势可能是聚合物表面分子运动能力增加和结晶程度变化等因素综合作用的结果.     

反应挤出接枝共聚反应表观链增长常数的测量

以预辐照的LLDPE反应挤出接枝MAA作为研究对象,通过在双螺杆挤出机中的不同部位取样,用FTIR分析接枝物及均聚物的产量,并用ESR测试链增长自由基浓度,设计了测定接枝和均聚反应初始阶段的表观链增长常数的方法.结果表明,在本实验测试范围内表观接枝链增长常数不同于均聚链增长常数;所得的测量值符合理论预测值,证明测试方法适合高温熔融体系的研究.     

具有相同臂长的系列星形聚苯乙烯的合成

星形聚合物可以作为研究高聚物支化效应的模型化合物。这方面工作已有报导。但是以多官能度的氯硅烷为偶联剂合成等臂长不同支化度的系列星形聚苯乙烯模型化合物的工作尚未见报导。本文报导了多官能度偶联剂和3、4、6、8、12臂的等臂长的系列星形聚苯乙烯样品的合成。     

Synthesis of Star-Shaped Polymers via Coordination of Bipyridyl-Terminated Polyoxyethylene with Metal Ions

Abstract

This paper describes the synthesis of various star-shaped polymers by means of complexation of bipyridyl-terminated polyoxyethylene with Ru(II) ion. Three kinds of bipyridyl-terminated polyoxyethylenes of different molecular weights were prepared from the corresponding polyoxyethylene monomethyl ethers with narrow molecular weight distributions. Bipyridyl was found to be introduced quantitatively at the end of the polymers based on the results of UV spectra. The formation of a star-shaped polymer was carried out by the reaction of RuCl₃ with three equivalents of bipyridyl-terminated polyoxyethylene. The UV spectrum of the star-shaped polymer obtained supported the formation of a typical Ru(II) tris(bipyridyl) complex. From the results of GPC, the star-shaped polymer obtained had a higher molecular weight than the pre-polymer and showed a narrow molecular weight distribution. In the case of a Ni(II) or a Co(II) complex, however, the star-shaped polymer was found to be dissociated into three linear prepolymers under the conditions of GPC measurement.     

溶液法星型聚乳酸的合成与表征

探讨了采用辛酸亚锡为催化剂,多元醇及多元酸为引发剂,以溶液法制备星型聚乳酸的可行性,研究了不同引发剂对产物分子量的影响.采用核磁共振及DSC对产物进行了表征,结果表明:以溶液法合成星型聚乳酸是可行的,但与丙交酯开环聚合制备星型聚乳酸的方法相比,溶液法在产物结构和分子量控制上并不十分有效,由于反应受到多官能团核引发剂空间位阻和反应概率的影响,聚乳酸产物的结构除星型结构外也同时存在大量的线型结构.     

Electrical Properties of a Highly Charged Cylindrical Particle in a Symmetric Electrolyte Solution

Based on the extended Langmuir's method, accurate analytic expressions for the electrical properties of cylindrical colloidal particle in a solution of symmetric electrolyte are derived from the nonlinear cylindrical Poisson-Boltzmann equation. Comparison is made with previous literature results. The present formulae have good agreement with literature values and are quite simple for practical use.     

Preparation of Polylactide Microspheres Having Positively or Negatively Charged Surfaces

The syntheses of polylactides (PLAs) with branched peptide end groups containing reactive (ionic) moieties such as amino or carboxyl groups are described and were used to prepare PLA‐based microspheres (MSs) with positively or negatively charged surfaces. Branched peptides with hydroxyl end groups and four protected amino or carboxyl groups, Boc₄‐K₃‐OH or Bn₄‐E₃‐OH, were synthesized, and the hydroxyl group converted to an alkoxide and was used as the initiation site for the ring‐opening polymerization of L ‐lactide. Subsequent deprotection gave PLAs end‐capped with branched peptides having four amino or carboxyl groups, respectively (K₃‐PLA and E₃‐PLA). K₃‐PLA and E₃‐PLA were converted to K₃⁴⁺‐PLA and E₃^4?‐PLA by acid or base treatment, respectively. MSs with charged surfaces were then prepared using K₃⁴⁺‐PLA or E₃^4?‐PLA as a surfactant [MS(K₃⁴⁺‐PLA) or MS(E₃^4?‐PLA)]. The ionic surface state of the MSs was confirmed by colloidal titration and zeta potential analysis.

SEM image of MSs: MS(K₃⁴⁺‐PLA).     

Ultrasonic Solution Degradations of Polystyrene and Substituted Polystyrenes in Tetrahydrofuran as Solvent

Abstract

Ultrasonic (70 W, 20 kHz) solution (2% THF) degradations of polystyrene (PS), poly(α-methylstyrene) (PαMeS), poly(p-isopropyl α-methylstyrene) (PpiPrαMeS), poly(p-chlorostyrene) (PpCIS), poly(p-bromostyrene) (PpBrS), and poly(p-methoxystyrene) (PpOMeS) have been carried out in tetrahydrofuran at 27° C. The average number of chain scissions S (where S = [(M _n)₀/(M _n)_t] - 1), computed from the overall values of [(M _n)₀ and (M _n)_t, were found to be different from those of S' (where S' = α([(M _n)₀/(M _n)_t] - 1)) based on the component (only that part of the polymer which is involved in degradation) data of the weight fraction (α), (M _n)₀, and (M _n)_t), S' for polystyrene and substituted polystyrene follows the order PS gt; PpCIS gt; PpiPrαMeS gt; PpBrS gt; PpOMeS gt; PαMeS. In the case of PS where degradations were also carried out at -20°C, lowering of the temperature increased the weight fraction of polymer degraded as well as S. Based on the viscosity and GPC data, it is concluded that the ultrasonic solution degradation of PS does not lead to branched polymers.     

Synthesis of Star-Shaped Macromolecular Schiff Base Complexes Having Melamine Cores and Their Magnetic and Thermal Behaviors

Abstract

We aim to study magnetic and thermal behaviors of some melamine cored macromolecular Schiff base complexes. In this context, tripodal ligands were synthesized by reacting melamine with 4-carboxybenzaldehyde or 4-hydroxybenzaldehyde. Then, 16 new trinuclear Fe(III), Cr(III), Mn(III), and Al(III) complexes were synthesized by reacting the ligands [tris-(4-carboxybenzimino)-1,3,5-triazine) or tris-(4-hydroxybenzimino)-1,3,5-triazine)] with pentadentate Schiff bases N,N′-bis(1-hydroxy-2-benzyliden)-1,7-diamino-4-azaheptane or N,N′-bis(salicylidene)pyridine-2,6-diamine. Later, ligands and complexes were characterized by means of elemental analysis, infrared spectroscopy, ¹H NMR, liquid chromatography–mass spectrometry, thermal analyses, and magnetic susceptibility measurements. Finally, metal ratios of the prepared complexes were determined by using atomic adsorption spectrometry. The complexes were also characterized as distorted octahedral high-spin d ³ (S = 3 × 1/2) Cr(III), high-spin d ⁵ (S = 5 × 1/2) Fe(III), low-spin d ⁴ (S = 2 × 1/2) Mn(III), and diamagnetic Al(III) bridged by ?OH group of COO^? or OH group of phenol.     

Charge States of y Ions in the Collision-Induced Dissociation of Doubly Charged Tryptic Peptide Ions

Bonds that break in collision-induced dissociation (CID) are often weakened by a nearby proton, which can, in principle, be carried away by either of the product fragments. Since peptide backbone dissociation is commonly charge-directed, relative intensities of charge states of product y- and b-ions depend on the final location of that proton. This study examines y-ion charge distributions for dissociation of doubly charged peptide ions, using a large reference library of peptide ion fragmentation generated from ion-trap CID of peptide ions from tryptic digests. Trends in relative intensities of y²⁺ and y¹⁺ ions are examined as a function of bond cleavage position, peptide length (n), residues on either side of the bond and effects of residues remote from the bond. It is found that y_n-2/b₂ dissociation is the most sensitive to adjacent amino acids, that y²⁺/y¹⁺ steadily increase with increasing peptide length, that the N-terminal amino acid can have a major influence in all dissociations, and in some cases other residues remote from the bond cleavage exert significant effects. Good correlation is found between the values of y²⁺/y¹⁺ for the peptide and the proton affinities of the amino acids present at the dissociating peptide bond. A few deviations from this correlation are rationalized by specific effects of the amino acid residues. These correlations can be used to estimate trends in y²⁺/y¹⁺ ratios for peptide ions from amino acid proton affinities.     

二甲苯异构体双电荷离子和单电荷离子的动能谱研究

利用质量分析离子动能谱和碰撞诱导解离技采研究了邻、间、对二甲苯分子在电子轰击质谱中产生的双电荷离子[C8H10]2+、[C8H9]2+和单电荷离子[C8H10]+。根据测定的电荷分离反应的释放动能T和由此估算的双电荷离子电荷分离反应过渡态两电荷间距R,推测出过渡态的结构,利用单电荷离子[C8H10]+的MIKES/CID谱可区分邻二甲苯与间、对二甲苯异构体.     

一些双电荷离子的气相碎裂反应

借助质量分析离子动能谱和串联质谱研究了由电子轰击产生的双电荷离子的单分子亚稳碎裂及碰撞诱导分解过程,讨论了两种实验方法导致的差别因素.此外,根据质量分析离子动能谱提供的双电荷离子电荷分离反应的动能释放值计算了两电荷中心间距的最小值,以判别按不同电荷分离方式碎裂的双电荷离子的过渡态结构.     

Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron‐Donating Groups

The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.     

Synthesis and Solution Properties of Loose Polymer Brushes Having Polyimide Backbone and Methylmethacrylate Side Chains

Summary: Graft-copolymers with polyimide backbone and PMMA side chains are synthesized by ATRP of methylmethacrylate on the polyimide macroinitiator. The obtained copolymers, macroinitiator, and cleaved side chains are investigated by ¹H NMR, SEC, static and dynamic light scattering, sedimentation, and viscosimetry in solutions. The synthesized copolymer is relatively loose polymer brushes: the average distance between grafted PMMA chains is ∼11 nm (4 repeat units of the backbone). The hydrodynamic and conformational characteristics of graft-copolymers change on passage from ethylacetate to chloroform due to difference in the thermodynamic quality of the solvents with respect to the copolymer components. The backbone is characterized more extended conformation than individual polyimide macromolecule.     

星形SIS嵌段共聚物的动态力学性能

本文报导了用粘弹谱仪对组成相同、支链分子量相同而支化度不同的,以及支化度相同、支链分子量不同的系列星形SIS嵌段共聚物的测试结果,实验发现:支链分子量是影响各相玻璃化转变温度和动态杨氏模量E′的主要因素,支化度对各相玻璃化温度影响很小,但是对E′影响是明显的。     

Complex-Forming Properties of Ceftazidime with Fe(III) Ions in an Aqueous Solution

In the present study, the complexing properties of ceftazidime with Fe(III) ions in aqueous solutions were characterized by UV-vis spectrophotometric and potentiometric methods. Using the UV-vis spectrophotometric method, the absorbance values for Fe(III) ions, a third-generation cephalosporin antibiotic (ceftazidime), and the Fe(III)-ceftazidime system were determined. Based on pH-metric studies, the value of the stability constant for the Fe(III)-ceftazidime complex was calculated.     

Thermoresponsive Star-Shaped Poly(2-isopropyl-2-oxazoline) in Aqueous Solution

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazoline) with t-butylcalix[8]arene core was studied by light scattering methods in aqueous solution. The sample under investigation has M_w = 19600 g mol^?1 and PDI of arms 1.41. The bimodal distribution of scattering objects was observed even at room temperature. The redistribution of these two kinds of particles takes place at T = 27°–36°C. At higher temperatures the growth of large particles, disappearance of the small component, and appearance-disappearance of “middle-size” aggregates were observed. Only the large particles with the hydrodynamic radius 95 nm exist in proximity to LCST (37.5°C).