bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformational temperature dependence of a poly(ethylene‐co‐acrylic acid) stationary phase investigated by nuclear magnetic resonance spectroscopy and liquid chromatography
Authors: Meyer Christoph , Pascui Ovidiu , Reichert Detlef , Sander Lane C. , Wise Stephen A. , Albert Klaus 
Published: March 2006

AbstractA polymer‐based RP sorbent was prepared by immobilizing a poly(ethylene‐co‐acrylic acid) copolymer with an acid mass fraction of 5% on silica by using a 3‐glycidoxypropyl linkage. 13C cross‐polarization/magic angle spinning NMR spectroscopy of the sorbent, either in the dry state or suspended in the mobile phase, showed an increase in mobility at elevated temperatures. Alkyl chain segments with gauche conformations were more mobile than chain segments with trans conformations. The strength of the 13C‐1H dipolar couplings in the alkyl chains was measured using the constant time dipolar and chemical shift pulse sequence, revealing less molecular motion for the trans conformation. Non‐linear van't Hoff plots were observed for separations of shape‐constrained solutes (such as geometric β‐carotene isomers and polycyclic aromatic hydrocarbons). At higher temperatures, the retention behavior was similar to that of monomeric C18 sorbents, whereas at ambient and lower temperatures, enhanced shape‐selective properties were exhibited similar to those of polymeric C30 sorbents.
Preparation and application of HPLC chiral stationary phases based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid
Authors: Hyun Myung Ho 
Published: March 2006

AbstractPreparation of liquid chromatographic chiral stationary phases (CSPs) based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid and their application are reviewed. The various methods of connecting (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid to silica gel covalently or dynamically are demonstrated. The CSPs based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid have been very successful for the resolution of various primary amino compounds with the use of an aqueous mobile phase containing organic and acidic modifiers. In addition, the resolution of secondary amino compounds including β‐blockers and N‐(3,5‐dinitrobenzoyl)‐α‐amino acids has been demonstrated on a CSP based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid with a non‐aqueous mobile phase.
Synthesis and HPLC evaluation of carboxylic acid phases on a hydride surface
Authors: Pesek Joseph J. , Matyska Maria T. , Gangakhedkar Surekha , Siddiq Rukhsana 
Published: March 2006

AbstractThree organic moieties containing carboxylic acid functional groups are attached to a particulate silica surface through silanization/hydrosilation. Two compounds (undecylenic acid and 10‐undecynoic acid) have 11 carbon chains and the other is a five‐carbon acid (pentenoic acid). Bonding is confirmed through carbon elemental analysis, diffuse reflectance infrared fourier transform spectroscopy, and carbon‐13 and silicon‐29 CP‐MAS NMR spectroscopy. The bonded phases are tested by HPLC using PTH amino acids, nucleic acids, theophylline‐related compounds, anilines, benzoic acid compounds, choline, and tobramycin. The latter two compounds are used to investigate the aqueous normal phase properties of the three bonded materials.
HPLC separation of fullerenes on two charge‐transfer stationary phases
Authors: Yu Qiong‐Wei , Shi Zhi‐Guo , Lin Bo , Wu Yan , Feng Yu‐Qi 
Published: March 2006

AbstractTwo charge‐transfer stationary phases were prepared by immobilizing p‐nitrobenzoic acid and naphthyl acetic acid onto silica. The nitrophenyl moiety and the naphthyl moiety were grafted to silica gel through the spacer of aminoalkyl silanes. The HPLC separation of C60, C70, and higher fullerenes on the new stationary phases was also studied. The influence of mobile phase and column temperature on the separation of C60 and C70 was examined, respectively. The retentions of C60 and C70 on the two stationary phases increased with decreasing toluene content in the mobile phase or with increasing column temperature. Higher fullerenes can be separated well using toluene as the mobile phase on the stationary phase of p‐nitrobenzoic acid‐bonded silica.
Immobilized polymeric stationary phases using metalized silica supports
Authors: Faria Anizio M. , Jardim Isabel C. S. F. , Collins Kenneth E. , Collins Carol H. 
Published: March 2006

AbstractImmobilized presynthesized polymers on porous metalized (zirconized or titanized) silica particles as new stationary phases with improved chemical stability for RP‐HPLC are reviewed. The preparations using different polymers, such as poly(methyloctylsiloxane), poly(methyltetradecylsiloxane), and poly(butadiene), different immobilization steps (gamma radiation, thermal treatment, and microwave radiation), and the chromatographic performances of these phases for polar, apolar, acidic, and basic compounds are discussed. The stability of some of these stationary phases using alkaline mobile phases is also presented.
An overview of the chromatographic properties and stability of C18 titanized phases
Authors: Silva César R. , Collins Carol H. , Collins Kenneth E. , Airoldi Claudio 
Published: March 2006

AbstractPhases based on titanized silicas are an alternative in the search for HPLC stationary phases with enhanced pH stability. This technology explores the chemical modification of the bare silica surface by grafting a titanium oxide layer with the objective of retarding the dissolution of the support in alkaline mobile phases, followed by C18 silanization. The present manuscript describes recent work on the development of chemically bonded titanized phases, including phases containing embedded urea groups, and phases prepared both in the absence and in the presence of a monolayer of water preadsorbed onto the bare silica. The advantages and disadvantages of these alternative C18 titanized phases are discussed, taking into account their chromatographic properties accessed by some common test procedures. Column lifetimes, measured by accelerated aging tests using aggressive conditions, such as high‐pH phosphate mobile phases and elevated temperature, are also discussed.
Twenty years of research on silica‐based chiral stationary phases
Authors: Cancelliere Giovanna , D'Acquarica Ilaria , Gasparrini Francesco , Maggini Michele , Misiti Domenico , Villani Claudio 
Published: March 2006

AbstractThis review provides an overview of twenty years of pioneering work (from 1985 to 2005) of our research group in the preparation and application of enantioselective packing materials for HPLC. After a brief introduction to the rational design of a new chiral stationary phase, a detailed presentation in chronological order of appearance in the literature is given of the currently developed repertoire of chiral stationary phases and their typical applications. Emphasis is placed on the different synthetic strategies exploited to obtain highly efficient, stable, and versatile chiral stationary phases.
Poly(ε‐Caprolactone)/Chitin and Poly(ε‐Caprolactone)/Chitosan Blend Films With Compositional Gradients: Fabrication and Their Biodegradability
Authors: Honma Tomonori , Zhao Li , Asakawa Naoki , Inoue Yoshio 
Published: March 2006

AbstractSummary: Poly(ε‐caprolactone) (PCL)/chitin and PCL/chitosan blend films with compositional gradients were successfully fabricated by a dissolution/diffusion method; that is, repeatedly pouring the PCL/chitin (or PCL/chitosan) blend solutions, with variable composition, onto polysaccharide layers. The compositional gradient structure in the resulting films was characterized by polarized optic microscopy, ATR‐FT‐IR and trans‐FT‐IR microscopic spectroscopy. Enzymatic degradability of the PCL/chitin and PCL/chitosan blend films with compositional gradients in the presence of lysozyme was compared with those of homogeneous films and two‐layer films. It was found that the degradation rate of PCL/chitin blend films with a compositional gradient was far lower than that of the neat chitin film, whereas the degradation rate of PCL/chitosan blend films with a compositional gradient was close to that of the neat chitosan film. The suppression of the chitosan crystallization, which accelerates the enzymatic degradation, at the surface of PCL/chitosan films with a compositional gradient was much more severe than that for PCL/chitin films with a compositional gradient.Polarized optical microscopy micrographs of cross sections of (a) PI2lay, (b) PIgrad, (c) PO2lay, and (d) POgrad.magnified imagePolarized optical microscopy micrographs of cross sections of (a) PI2lay, (b) PIgrad, (c) PO2lay, and (d) POgrad.
NMR Spectroscopy and MALDI‐TOF MS Characterisation of End‐Functionalised PVP Oligomers Prepared with Different Esters as Chain Transfer Agents
Authors: Ranucci Elisabetta , Ferruti Paolo , Annunziata Rita , Gerges Irini , Spinelli Giuseppe 
Published: March 2006

AbstractSummary: Ester‐functionalised poly(1‐vinylpyrrolidin‐2‐one) (PVP) oligomers obtained by radical polymerisation in methyl propionate, diethyl malonate and diethyl 2‐methylmalonate were characterised by NMR spectroscopy, and MALDI‐TOF mass spectrometry. The chain‐transfer constants were determined as 5.54 × 10−4, 1.22 × 10−3 and 1.70 × 10−2, respectively, by measuring the variation of the number‐average molecular weight on conversion. These values were compared with those of methyl isobutyrate (1.65 × 10−3) and ethyl lactate (1.03 × 10−2), which had been previously determined. A clear dependence was found on the reactivity of the mobile hydrogen atoms α with the ester group. All of the macromolecules carried a single ester function. Therefore, the re‐initiation step by the CTA‐derived radicals overwhelmingly prevailed over initiation by the primary radicals.MALDI‐TOF mass spectra of broad‐distribution, end‐functionalised PVP oligomers, analysed in an HCCA matrix. a): PVPL; MALDI molecular weights: $\overline M _{\rm n}$ = 3 465; $\overline M _{\rm w}$ = 3 891; polydispersity index = 1.12. b) PVPM; MALDI molecular weights: $\overline M _{\rm n}$ = 2 272; $\overline M _{\rm w}$ = 2 775; polydispersity index = 1.22.magnified imageMALDI‐TOF mass spectra of broad‐distribution, end‐functionalised PVP oligomers, analysed in an HCCA matrix. a): PVPL; MALDI molecular weights: $\overline M _{\rm n}$ = 3 465; $\overline M _{\rm w}$ = 3 891; polydispersity index = 1.12. b) PVPM; MALDI molecular weights: $\overline M _{\rm n}$ = 2 272; $\overline M _{\rm w}$ = 2 775; polydispersity index = 1.22.
Highly Branched Poly(arylene ether)s via Oligomeric A2 + B3 Strategies
Authors: Lin Qin , Unal Serkan , Fornof Ann R. , Yilgor Iskender , Long Timothy E. 
Published: March 2006

AbstractSummary: Branched poly(arylene ether)s were prepared in an oligomeric A2 + B3 polymerization of phenol endcapped telechelic poly(arylene ether sulfone) oligomers as A2 and TFPPO as trifunctional monomer B3. The molar mass of the A2 oligomer significantly influenced the onset of gelation and the DB. A high level of cyclization during polymerization of low molar mass A2 oligomers (U3 = 660 and U6 = 1 200 g · mol−1) led to a high conversion of functional groups in the absence of gelation, and the level of cyclization reactions in the polymerization decreased as the molar mass of the A2 oligomer was increased. The pronounced steric effect in the polymerization of higher molar mass A2 oligomers (U8 = 1 800 and U16 = 3 400 g · mol−1) resulted in low reactivity of the third aryl fluoride in the B3 monomer. As a result, only slightly branched (U8 = 1 800 g · mol−1) or nearly linear (U16 = 3 400 g · mol−1) high molar mass products were obtained with higher molar mass A2 oligomers. The branched polymers exhibited lower Mark‐Houwink exponents and [η] relative to linear analogs, and differences between the branched polymers and linear analogs were less significant as the molar mass of the A2 oligomers was increased due to a decrease in the overall DB.
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Stabilizer‐Free Dispersion Copolymerization of Maleic Anhydride and Vinyl Acetate. II. Polymerization Features
Authors: Xing Chang‐Min , Yu Yong , Yang Wan‐Tai 
Published: March 2006

AbstractSummary: The polymerization features of the novel stabilizer‐free dispersion copolymerization of MAn and VAc were studied. It was found that the dispersion copolymerization of MAn/VAc is a fairly rapid process, which starts from a slow solution polymerization (below 10% conversion, Stage I) and follows a drastic increase of polymerization rate (10–80% conversion, Stage II) due to the known gel effect. Such process was accompanied by the increase of molecular weight of the copolymer formed ($\overline M _{\rm n}$ from 1.2 × 104 to 3.8 × 104 g · mol−1) and the broadening of the molecular weight distribution ($\overline M _{\rm w} /\overline M _{\rm n}$ from 2.4 to 8.0). Ea of Stage I was determined to be 76.7 kJ · mol−1, while the value of Stage II was 64.7 kJ · mol−1. The lower Ea in Stage II than that in Stage I suggests that there exists a shift of polymerization locus from the solution phase to the particle phase. Moreover, we found that the initial rate of polymerization increased with monomer concentration as well as initiator concentration, following the relationship (Rp)i ∝ [MAn + VAc] · [BPO]. This further implies that the dispersion copolymerization mainly proceeds as a solution polymerization in the very early stage.Evolutions of the stabilizer‐free dispersion copolymerization of MAn and VAc with butyl acetate as reaction medium and the solution copolymerization with methyl propyl ketone as solvent.magnified imageEvolutions of the stabilizer‐free dispersion copolymerization of MAn and VAc with butyl acetate as reaction medium and the solution copolymerization with methyl propyl ketone as solvent.
Nanosized‐Silica‐Reinforced Holographic Polymer‐Dispersed Liquid Crystals
Authors: Kim Eun Hee , Woo Ju Yeon , Kim Byung Kyu 
Published: March 2006

AbstractSummary: Nanosized silicas added to holographic polymer‐dispersed liquid crystals (HPDLC) provide the resin phase with increased elasticity, dimensional stability, and the high diffraction efficiency of the gratings. On the other hand, nucleation and growth of periodic modulation are delayed, especially with small‐sized silica because of the increased viscosity of the resin mixture. Effects of the LC/resin composition and cell gap on the diffraction efficiency have also been studied.AFM image of silica added HPDLC.magnified imageAFM image of silica added HPDLC.
Kinetic Studies upon the Influence of Cyclodextrin on the Polymerization of Methacrylamides in Homogenous Aqueous Solution
Authors: Steffens Christopher , Choi Soo Whan , Ritter Helmut 
Published: March 2006

AbstractSummary: N‐methacryloyl‐1‐aminopropane (1), N‐methacryloyl‐1‐aminobutane (2), N‐methacryloyl‐1‐aminopentane (3), and N‐methacryloyl‐1‐aminohexane (4) are synthesized and treated with an aqueous solution of randomly methylated β‐cyclodextrin (Me‐β‐CD) to form the water‐soluble host‐guest complexes 1a–4a. In case of the aqueous polymerization of the free monomers 1–4 the initial polymerization rate increases with increasing water solubility. The opposite effect is observed in the case of the polymerizations of the Me‐β‐CD‐complexed methacrylamide monomers 1a–4a. The polymerization rates are increased with increasing alkyl chain length of the complexed monomers 1a–4a and decreasing water solubility of the free monomers 1–4.Initial polymerization rate v0 of CD‐complexed monomers 1a–4a (○) vs. water solubilities of monomers 1–4 (▪).magnified imageInitial polymerization rate v0 of CD‐complexed monomers 1a–4a (○) vs. water solubilities of monomers 1–4 (▪).
Poly(dicyclopentadiene) Submicron Fibers Produced by Electrospinning
Authors: Bellan Leon M. , Coates Geoffrey W. , Craighead Harold G. 
Published: March 2006

AbstractSummary: We have used the process of electrospinning to produce fibers of poly(dicyclopentadiene) with diameters on the submicron scale. The material, formed from a monomer‐catalyst solution, polymerized in flight during the electrospinning process. Fibers were collected over trenches etched in silicon and the Young's moduli were measured using an atomic force microscope to measure force‐displacement curves. The resulting values of Young's moduli are larger than typical values for bulk polymer material.SEM image of suspended PDCPD fiber.magnified imageSEM image of suspended PDCPD fiber.
Synthesis and Characterization of Novel pH‐Responsive Polyampholyte Microgels
Authors: Tan Beng Hoon , Ravi Palaniswamy , Tam Kam Chiu 
Published: March 2006

AbstractSummary: We synthesized for the first time novel pH‐responsive polyampholyte microgels consisting of poly(methacrylic acid) and poly(2‐(diethylamino)ethyl methacrylate) (PMAA‐PDEA) that are sterically stabilized with poly(ethylene glycol) methyl ether methacrylate (PEGMEM). These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH but become hydrophobic and compact between pH 4 and 6 near the isoelectric point. Dynamic‐light scattering measurements showed that the hydrodynamic radius, Rh of these microgels is approximately 100 nm between pH 4 and 6 and increases to around 140 and 170 nm at pH 2 and 10, respectively. It is evident that the cross‐linked MAA‐DEA microgel that is sterically stabilized with PEGMEM retains the polyampholyte properties in solution.Sterically stabilized cross‐linked MAA‐DEA microgel.magnified imageSterically stabilized cross‐linked MAA‐DEA microgel.
Confocal Raman Microspectroscopy: Calculation of Corrected Depth Profiles of Wet‐Chemically Modified Polymer Films
Authors: Gallardo Alberto , Spells Stephen , Navarro Rodrigo , Reinecke Helmut 
Published: March 2006

AbstractSummary: A mathematical approach developed to correct depth profiles of wet‐chemically modified polymer films obtained by confocal Raman microscopy is presented which takes into account scattered contributions originated from a diffraction‐limited laser focal volume and the refractive index of the sample. The method is demonstrated in both virtual and real samples where it is shown that considerable differences between apparent and corrected depth profiles exist at the surface, especially when profiles with strong concentration gradients are dealt with or an instrument with poor depth resolution is used.Comparison of depth profiles obtained by simple normalization (solid line) and normalization after correction of the data with respect to diffraction effects.magnified imageComparison of depth profiles obtained by simple normalization (solid line) and normalization after correction of the data with respect to diffraction effects.
Thermal and Surface Properties of Phenolic Nanocomposites Containing Octaphenol Polyhedral Oligomeric Silsesquioxane
Authors: Lin Han‐Ching , Kuo Shiao‐Wei , Huang Chih‐Feng , Chang Feng‐Chih 
Published: March 2006

AbstractSummary: We have synthesized a new polyhedral oligomeric silsesquioxane (POSS) containing eight phenol functional groups and copolymerized it with phenol and formaldehyde to form novolac‐type phenolic/POSS nanocomposites exhibiting high thermal stabilities and low surface energies. Our DSC results indicate that the glass transition temperature of these nanocomposites increased initially upon increasing their POSS content, but then decreased at POSS content above 10 wt.‐%, presumably because of the formation of relatively low molecular weight species and POSS aggregation as evidenced from MALDI‐TOF mass analyses. Our TGA analyses indicated that the 5‐wt.‐%‐mass‐loss temperatures (Td) increased significantly upon increasing the POSS content because the incorporation of the POSS led to the formation of an inorganic protection layer on the nanocomposite's surface. XPS and contact angle data provided positive evidence to back up this hypothesis. In addition, contact angle measurements indicated a significant enhancement in surface hydrophobicity after increasing the POSS content.Syntheses procedures of phenolic/OP‐POSS nanocomposites.magnified imageSyntheses procedures of phenolic/OP‐POSS nanocomposites.
Preparation of Well‐Defined PVOH/C60 Nanohybrids by Cobalt‐Mediated Radical Polymerization of Vinyl Acetate
Authors: Detrembleur Christophe , Stoilova Olya , Bryaskova Rayna , Debuigne Antoine , Mouithys‐Mickalad Ange , Jérôme Robert 
Published: March 2006

AbstractSummary: Poly(vinyl acetate) chains end‐capped by a Co(acac)2 complex [PVAc‐Co(acac)2] were prepared by bulk cobalt‐mediated radical polymerization (CMRP) of vinyl acetate and used for grafting fullerene (C60) with four PVAc arms at low temperature (30 °C). A photoactive water‐soluble poly(vinyl alcohol)/C60 nanohybrid was then prepared by hydrolysis of the PVAc arms of the nanohybrid. Because of photoactivity and very low cytotoxicity, this type of water‐soluble nanohybrid is very promising for the photodynamic cancer therapy.Strategy for the preparation of PVAc/C60 nanohybrid and hydrolysis of PVAc/C60 nanohybrid into PVOH/C60 nanohybrid.magnified imageStrategy for the preparation of PVAc/C60 nanohybrid and hydrolysis of PVAc/C60 nanohybrid into PVOH/C60 nanohybrid.
Micro FTIR Mapping of Nanometer Ferroelectric Polymer Films
Authors: Eidelman Naomi , Tsutsumi Naoto , Chiang Chwan‐Kang 
Published: March 2006

AbstractSummary: Highly crystalline ferroelectric polymer films [vinyidene fluoride and trifluoroethylene, β‐P(VDF‐TrFE), 260–15 nm thick] were characterized with FTIR reflectance‐transmission microspectroscopy (FTIR‐RTM) mapping technique (400 µm × 400 µm spatial resolution). The amorphous and crystalline fractions were identified locally. FTIR‐RTM maps (1 cm2 area) provided a unique in‐depth view of the ultrathin films. Lower film thickness suppressed growth of the crystalline phase. Increased content of amorphous phase lead to non‐uniform films with degraded ferroelectric behavior.FTIR‐RTM maps of the distribution of the amorphous phase in the 80 and 35 nm films.magnified imageFTIR‐RTM maps of the distribution of the amorphous phase in the 80 and 35 nm films.
Synthesis of Novel Biomimetic Zwitterionic Phosphorylcholine‐Bound Chitosan Derivative
Authors: Zeng Rong , Fu Hua , Zhao Yufen 
Published: March 2006

AbstractSummary: Water‐soluble biomimetic chitosan derivative conjugating zwitterionic phosphorylcholine was efficiently prepared through Atherton‐Todd reaction under the mild conditions, and the possible formation mechanism of zwitterionic product was related to the nucleophilic attack of adjacent 3‐hydroxyl on the D‐glucosamine residue to phosphorus with the help of base. UV absorption and melting behaviors of DNA/phosphorylcholine‐bound chitosan derivative showed that the phosphorylcholine‐bound chitosan derivative could be a new carrier for long‐circulating macromolecular drug delivery.Structure of zwitterionic PC‐chitosan.magnified imageStructure of zwitterionic PC‐chitosan.
Prediction of Chemical‐Physical Properties by Neural Networks for Structures
Authors: Duce Celia , Micheli Alessio , Solaro Roberto , Starita Antonina , Tiné Maria Rosaria 
Published: March 2006

AbstractHere we present an overview of a new approach to cheminformatics based on recursive neural networks. This approach allows for combining the flexibility and advantages of neural networks with the representational power of structured domains. Current advances, which include applications to the prediction of the solvation free energy of small molecules in water and of the glass transition temperature of (meth)acrylic polymers are reported.
Biodegradable Fibers of Poly‐L, DL‐lactide 70/30 Produced by Melt Spinning
Authors: Fambri Luca , Bragagna Stefano , Migliaresi Claudio 
Published: March 2006

AbstractMelt spinning of poly‐L, DL‐lactide 70/30 has been studied. Fiber having diameter lower than 120 micron exhibited tensile modulus and strength in the range of 3–4 GPa and 130–180 MPa, respectively. Maximum attainable modulus and strength of 4.7 GPa and 205 MPa were predicted, according to a proposed equation in dependence on the draw ratio. In vitro degradation performed in PBS solution at 37 °C, showed that after 4 weeks fibers maintained adequate properties for tissue engineering applications.