Stable,High‐Molecular‐Weight Poly(phthalaldehyde)

Low ceiling temperature, thermodynamically unstable polymers have been troublesome to synthesize and keep stable during storage. In this study, stable poly(phthalaldehyde) has been synthesized with BF₃‐OEt₂ catalyst. The role of BF₃ in the polymerization is described. The interaction of BF₃ with the monomer is described and used to maximize the yield and molecular weight of poly(phthalaldehyde). Various Lewis acids were used to investigate the effect of catalyst acidity on poly(phthalaldehyde) chain growth. In situ nuclear magnetic resonance was used to identify possible interactions formed between BF₃ and phthalaldehyde monomer and polymer. The molecular weight of the polymer tracks with polymerization yield. The ambient temperature stability of poly(phthalaldehyde) was investigated and the storage life of the polymer has been improved. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 55, 1166–1172     

Radical ring-opening polymerization of lipoates: Kinetic and thermodynamic aspects

The radical ring-opening polymerization of a lipoate-based monomer, ethyl lipoate, in bulk and in solution was studied at various temperatures and it was found that in all cases, only limited (plateau) conversions were reached, which were lower at higher temperatures and/or at higher dilutions. It was established that a monomer-polymer equilibrium exists with a corresponding ceiling temperature of 139°C. Due to the reversibility of the lipoate polymerization, when poly(ethyl lipoate) was heated to 150°C, it degraded and within 3 h, the molecular weight decreased to less than 15% of the initial value. Likewise, when the polymer was dissolved in anisole and a radical initiator was added, degradation was observed even at 60°C and it became increasingly pronounced at higher concentrations of the radical source. Due to the presence of multiple disulfide groups in the backbone, poly(ethyl lipoate) also degraded in the presence of reducing agents, such as tributylphosphine, yielding the reduced (dithiol) form of the monomer, ethyl dihydrolipoate.     

Determination of microstructure and glass-transition temperature of acrylonitrile-methyl acrylate copolymers by 13C-NMR spectroscopy

Acrylonitrile-methyl acrylate (A/M) copolymers of different monomer compositions were prepared by bulk polymerization using free radical initiator (benzoyl peroxide). Copolymer compositions were determined by elemental analyses and comonomer reactivity ratios were determined by the nonlinear least squares errors-in-variables methods (EVM). Terminal and penultimate reactivity ratios have been calculated using the observed monomer triad sequence distribution determined from ¹³C{¹H}-NMR spectra. The triad sequence distribution was used to calculate diad concentrations, conditional probability parameters, number-average sequence lengths, and run number in the copolymers. The observed triad sequence concentrations determined from ¹³C{¹H}-NMR spectrum agreed well with those calculated from reactivity ratios. Glass transition temperatures (T_g) of various copolymers determined from DSC gave good agreement with those obtained from NMR. © 1992 John Wiley & Sons, Inc.     

Investigation of drug release and 1H‐NMR analysis of the in situ forming systems based on poly(lactide‐co‐glycolide)

In situ forming biodegradable polymeric systems loaded with betamethasone (BTM) and betamethasone acetate (BTMA) were prepared using poly(DL ‐lactide‐co‐glycolide) (PLGA), ethyl heptanoate (EH), and N‐methyl‐2‐pyrrolidone (NMP) as the biodegradable polymer, additive, and solvent, respectively. The drug release studies were carried out in buffer (pH = 7.4, 37°C) using high performance liquid chromatography (HPLC). ¹H‐NMR was used to determine the polymer degradation behavior, release mechanism, and interactions between the polymer and drug. The ¹H‐NMR spectra showed that all interactions between the polymer and drug were hydrogen bonding. Hydroxyl groups and fluorine in drugs were involved in hydrogen bonding with PLGA polymer. In ¹H‐NMR studies, we found that the degradation rate in the systems loaded with BTMA was higher than the systems loaded with BTM because BTMA is only slightly soluble and accelerates the hydrolysis of PLGA chains. The formulations loaded with BTM had obviously lower burst release compared with BTMA loaded samples. With respect to ¹H‐NMR spectra, the mechanism of BTM release is controlled by two effective factors: solvent removal and polymer degradation. Copyright © 2008 John Wiley & Sons, Ltd.     

In situ scanning tunneling microscopy of oxide-supported metal clusters: nucleation,growth, and thermal evolution of individual particles

An experimental approach was developed for imaging the nucleation and growth of individual oxide-supported nanoparticles and their subsequent in situ chemical and thermal treatments by scanning tunneling microscopy (STM). The potential of the method is demonstrated for Au nanoparticles supported on a reduced TiO(2) substrate where a cluster-by-cluster comparison is made of the morphological evolution and stability of nanoparticles during their nucleation and thermal annealing. Using this methodology the details of the nucleation and growth kinetics can be directly observed.     

Reaction of Phthalaldehyde with Aminoethanol under Different Conditions: Products and Mechanisms of Their Formation

Analysis of amino acids and very efficient disinfection procedures are based on the reaction of phthalaldehyde (OPA) with primary amines. In this contribution, aminoethanol (=kolamin) as a nitrogen‐containing nucleophile was used for the investigation of its reaction mechanism with OPA performed in basic aqueous buffered media (pH 9.5), where an influence of hydration or solvation is expected, and in anhydrous acetonitrile. Depending on the detailed reaction conditions, seven products were isolated and their structures determined by NMR, mass spectrometry, and X‐ray structure analysis. Reaction mechanisms are proposed, which involve hydride transfers to OPA (Cannizzaro‐type reaction).

     

缔合溶液热力学性质与谱学性质的关联

缔合溶液具有与理想溶液显著不同的热力学和谱学性质,对于热力学和谱学的研究,有助于我们理解缔合溶液的特殊行为.谱学技术中核磁共振(NMR)、红外(IR)和拉曼(Raman)光谱是研究分子间相互作用和溶液结构等微观性质的有效方法,谱学已成为分子热力学研究体系"四面体结构"中的第四个顶点.本文对缔合溶液中热力学(汽液平衡和焓)和谱学(NMR,IR和Raman)联系的最新研究进展进行了综述,着重介绍相关的模型,如化学缔合模型、局部组成(LC)、格子流体氢键(LFHB)理论以及统计缔合流体理论(SAFT).     

Conformational equilibria of trans -3-X-cyclohexanols (X = Cl, Br, CH3 and OCH3). A low temperature NMR study and theoretical calculations

The integration of 1H and 13C NMR spectra, at - 90 degrees C in CS2/CD2Cl2 (9:1), for the trans-3-chlorocyclohexanol (1), trans-3-bromocyclohexanol (2), and trans-3-methoxycyclohexanol (4) showed that the equatorial-axial (ea) conformer occurs as ca 63, 63, and 69% in the conformational equilibrium, respectively. This corresponds to the following DeltaG(ea-ae) values (from (1)H spectrum): - 0.32 +/- 0.01, - 0.32 +/- 0.04, - 0.48 +/- 0.05 kcal mol(-1); and to (from 13C spectrum): - 0.31 +/- 0.04, - 0.35 +/- 0.05, and - 0.44 +/- 0.01 kcal mol(-1), respectively, in very good agreement within both series. Thus, although bromine is bulkier than chlorine, the 1,3-diaxial steric effects are similar in these equilibria. However, the integration of (1)H NMR spectrum for the trans-3-methylcyclohexanol (3) gave 90% of the 3ae conformer in the equilibrium, at - 90 degrees C on CS2/CD2Cl2 (9:1), corresponding to a DeltaG(ea-ae) value of 1.31 +/- 0.02 kcal mol(-1). The values obtained through the additivity rule, with data from monosubstituted cyclohexanes (DeltaG(Ad) = DeltaG(X) + DeltaG(OH)), for compounds 1, 2, and 4 (-0.37 +/- 0.15, - 0.34 +/- 0.09, and - 0.46 +/- 0.04 kcal mol(-1), respectively) are in very good agreement with the experimental values, but it is significantly smaller for compound 3 (0.79 +/- 0.02 kcal mol(-1)). Theoretical calculations through different levels of theory (HF/6-311 + g**, B3LYP/6-311 + g**, MP2/6-31 + g**, and CBS-4M) showed that CBS-4M is the best method for the study of conformational equilibria for these systems, since it provides DeltaG(ea-ae) values similar to the experimental values.     

Self‐assembly and lower critical solution temperature properties of supramolecular block copolymer/ionic liquid complexes depending on the alkyl chain length of imidazolium rings

We report the liquid crystalline (LC) assembly and lower critical solution temperature (LCST) properties of wedge‐shaped block copolymer (BCP)/1‐alkyl‐3‐methylimidazolium tetrafluoroborate ([C_nMIM][BF₄], n = 2, 4, 6) complexes ( 1 – 3 ) depending on the alkyl chain length of the ionic liquids (ILs). In contrast to the crystalline BCP, all of the ionic samples showed LC phases. 1 with [C₂MIM][BF₄] exhibited a hexagonal columnar phase, and 3 with [C₆MIM][BF₄] exhibited a gyroid phase. Interestingly, a temperature‐dependent transformation from columnar phase to gyroid phase was revealed for 2 with [C₄MIM][BF₄]. The phase difference may be explained by the supramolecular shape change that was dependent on the alkyl chain length of the ILs. The LCST behavior was characterized using the differential scanning calorimetry, turbidity observations, and the X‐ray diffraction techniques. Notably, the primary d‐spacing began to decrease at the clouding temperature (T_c). 3 showed the highest T_c at 130 °C, which is greater than the temperature of the order‐to‐disorder transition. The results demonstrate that the subtle variation in the IL structure affects the morphological and LCST properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3587–3596     

A kinked unit‐containing thermotropic liquid crystalline copolyester with low glass transition temperature and broad phase transition temperature

A novel phosphorus‐containing thermotropic liquid crystalline copolyester with kinked unit named as poly(hydroxybenzate‐co‐DOPO‐benzenediol dihydrodipheyl ether terephthalate) (PHDDT) was synthesized successfully by melting transesterification from terephthalic acid (TPA), p‐hydroxybenzoic acid (p‐ABH), 2‐(6‐oxid‐6H‐dibenz(c, e) (1,2) oxaphosphorin 6‐yl)1,4‐benzenediol (DOPO‐HQ), and 4,4′‐dihydroxydiphenyl ether (DOP). The chemical structure, the mesophase behavior, and the thermal properties of the copolyesters were characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (¹H, ¹³C, and ³¹P NMR), wide‐angle X‐ray diffraction, polarizing light microscopy (PLM), differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical analysis. Results suggested that PHDDTs exhibited the typical nematic mesophase that occurred at low temperatures and maintained in a broad temperature range from 230 °C to higher than 400 °C, and had low glass transition temperature ranging from 154.5 to 166.9 °C. The novel phosphorus‐containing thermotropic liquid crystalline copolyester will have a potential application in preparing various in situ reinforced polymer materials with excellent mechanical properties and flame retardancy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4703–4709, 2009     

Crystallography and crystallite morphology of rutile synthesized at low temperature

Rutile was prepared at low temperature with titanium trichloride in an acid- and oxygen-rich environment. Samples were characterized with X-ray powder diffraction, transmission electron microscopy, and thermogravimetry; rutile's crystalline structure was refined with the Rietveld method. Crystallites were needles with their largest dimension along c lattice parameter; they grew in bundles parallel to their length axis, and contained hydroxyls in their lattice and on their surface. When samples were annealed, dehydroxylation generated lattice defects that produced microstrains and created conditions for crystallite sintering at temperatures above 300°C. Titanium-oxygen interaction in rutile depended on the annealing temperature, which gave rise to changes in the symmetry of the representative rutile titanium-oxygen octahedron. The atomic bond length between the oxygen atoms shared by adjacent octahedra decreased with the temperature, contracting the lattice. All this was caused by the variation of the number of hydroxyls in the lattice.     

Synthesis and self‐assembly behavior study of α,ω‐dicarboxyl‐poly(ethylene glycol)–permethyl‐6‐amino‐6‐deoxy‐β‐cyclodextrin‐monoamide: A new β‐cyclodextrin conjugate

A new type of amphiphilic macromolecule was synthesized through the attachment of a poly(ethylene glycol) chain to a permethyl‐amino‐β‐cyclodextrin ring. The structure of the product was studied with 1D and 2D NMR experiments and with MALDI‐TOF MS. The resulting comet‐shaped molecule showed self‐assembly behavior in polar solvents. The presence of supramolecular structures in aqueous media was detected with dynamic light scattering and proven also by 2D NOESY and DOSY experiments. The supramolecular structures that formed could serve as starting materials for new types of drug delivery bioconjugates containing two independent dopable sites, that is, the cyclodextrin ring and the core of the supramolecular structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5149–5155, 2007     

Assessment of COMT isolation by HIC using a dual salt system and low temperature

Sodium citrate (SC) and low temperatures between 7 and 5°C are effective in suppressing aggregation of proteins and may be beneficial to be included during a purification process. In this work, we analyzed the application of dual salt system, ammonium sulfate (AS) and SC on binding and elution conditions of recombinant hSCOMT on typical HIC sorbents. Specifically in butyl and octyl supports, the use of, respectively, 300 mm AS/200 mm SC and 25 mm AS/25 mm SC in the loading buffer resulted in complete binding of COMT. Elution was obtained by decreasing the ionic strength to 0 M of salt. For the delineate goal, it also favorably increased the support chain length while a consequent decrease in the dual ionic strength was observed for hSCOMT retention. In the presence of dual salt systems octyl media exhibited classic HIC behavior, good protein selectivity, an excellent purification factor and reduced denaturation effects of hSCOMT observed with higher salt concentrations. Also the inclusion of temperature control during the elution step appears to be advantageous for greater activity recovery without enzyme aggregation. In fact, these results could allow the prediction of most stabilizing conditions for this termolabile enzyme on the chromatographic stage, regarding salt types and therefore effectiveness to improve HIC selectivity and desirable purity on the target fractions. Copyright © 2009 John Wiley & Sons, Ltd.     

The high‐temperature tribological properties of Si‐DLC films

The tribological properties of Silicon‐containing diamond‐like‐carbon (Si‐DLC) films, deposited by magnetron sputtering Si target in methane/argon atmosphere, were studied in comparison with diamond‐like‐carbon (DLC) films. The DLC films disappeared because of the oxidation in the air at 500 °C, whereas the Si‐DLC films still remained, implying that the addition of Si improved significantly the thermal stability of DLC films. Retarded hydrogen release from DLC film at high temperature and silicon oxide on the surface might have contributed to lower friction coefficient of the Si‐DLC films both after annealing treatment and in situ high‐temperature environment. Copyright © 2012 John Wiley & Sons, Ltd.