Polymerisation et copolymerisation de monophenyl et de diphenylethylenes amorcees par des graphitures de metaux alcalins

The bulk polymerization at -24° of α-methylstyrene initiated by the alkali metals and the graphitides LiC₁₂, KC₂₄ and KC₃₆ has been studied. The tacticities of polymers have been measured by [¹H] NMR. The alkali metals give polymers having the same tacticity and the propagation of the stereoconfiguration is bernouillian; LiC₁₂ yields more racemic diads while KC₂₄ and KC₃₆ yield more meso diads and show a penultimate effect. By measuring the growing of the thickness of KC₂₄ flakes, it appears that the more sterically hindered a monomer the more slowly it penetrates into the graphitide. The copolymerizations at 25° of styrene with 1-1 diphenylethylene or 1–2 diphenylethylene (trans stilbene) (comonomer ratio 1/1) initiated by KC₂₄ in tetrahydrofuran (THF), xylene (XL), decahydronaphthalene (decalin DL) and cyclohexane (CH) have been studied. The amount of styrene units in the copolymers depends on the nature of the solvent: it increases as the interaction solvent-graphitide decreases. All the results support the view that the polymerization proceeds between the graphite layers.     

On semiclassical four‐point correlators in AdS5 × S5

Following the recent advances in the holographic calculation of n‐point correlation functions with two “heavy” (with large quantum numbers) states at strong coupling, we extend these findings by computing specific contributions to four‐point correlators of four heavy BMN operators in �� = 4 supersymmetric Yang–Mills theory.     

Synthesis and Properties of Hydrophilized Tertiaryamine Polymers Obtained by Graphitide-Initiated Anionic Copolymerization of a N,N-Disubstituted Aminothiirane with Oxiranes

Abstract

New functional aliphatic copolymers have been synthesized by an-ionic ring opening polymerization of N-methyl-N-sec-butyl-N-(thii-rane-2-ylmethyl) amine (Me-sBu, ESA) with either trimethylsilyl protected glycidol (TMSGE) or ethylene oxide (EO) using potassium graphitide KC₂₄ or sodium metal as initiators. Whenever TMSGE was present, TMSGE chain growing was perturbed by transfer reactions. Branched TMSGE homopolymers and Me-sBu, ESA/TMSGE copolymers were obtained with both the expected 1–3 polyglycidol and the unusual 1-4 poly(3-hydroxyoxetane) enchainments, as shown by ¹³C NMR. Copolymers of different compositions obtained by varying the Me-sBu, ESA/TMSGE feed composition from 85/15 to 35/65 or the Me-sBu, ESA/EO one from 76/24 to 64/36 were amorphous and random, as shown by DTA and ¹³C NMR studies. Copolymers with less than 20% of EO or TMSGE-derived units in the chain were soluble in water at pH < 4. Potentiometric titration curves showed the presence of a plateau (for the degree of neutralization α in the range 0.15 < α < 0.9) due to phase separation, as in the case of Me-sBu, ESA homopolymers. Copolymers with more than 50% of TMSGE units in the chain were soluble in water at pH < 7 and exhibited normal potentiometric titration curves with pH increasing progressively in the range 0.15 < α < 0.9. From these data, it is concluded that TMSGE- or EO-derived hydrophilic repeat units are unable to promote globular structure, in contrast to quaternary ammonium repeat units.     

N,N,N-trimethylchitosan iodide complexes with a weak or a strong polyacid and nanoparticles thereof

Polyelectrolyte complexes (PECs) were prepared from N,N,N-trimethylchitosan iodide (TMCh) of different molar mass and a weak polyacid-poly(acrylic acid) (PAA) or a strong polyacid-poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS). The quaternization of the amino groups of chitosan enabled the formation of water-insoluble PECs in a broad pH range—from 3 to 12 and from 1 to 12 for TMCh/PAA and TMCh/PAMPS, respectively. Whereas the stoichiometry of the TMCh/PAA complex was pH dependant, the stoichiometry of the TMCh/PAMPS complex did not depend on pH. The stoichiometry and the yield of the complexes were influenced by the molar mass of TMCh. PEC nanoparticles were produced by mixing dilute solutions of the oppositely charged polyelectrolytes as revealed by dynamic light scattering analyses. The size of the particles was in the range of 135–924 nm and depended on the polyelectrolyte molar mass, the initial polyelectrolyte concentration, and the molar fraction of the TMCh units. Microbiological screening against Staphylococcus aureus and Escherichia coli revealed that PECs between TMCh and PAA or PAMPS have a good antibacterial effect, which is more slowly pronounced than that of the starting TMCh of different molar mass.     

Darstellung von isotaktischem Polystyrol auf bin?ren K- Graphit-Inklusions-Verbindungen

Ohne Zusammenfassung     

Electrospun chitosan-coated fibers of poly(L-lactide) and poly(L-lactide)/poly(ethylene glycol): preparation and characterization

Fibrous poly(L-lactide) (PLLA) and bicomponent PLLA/poly(ethylene glycol) mats were prepared by electrospinning and then were coated with chitosan. The presence of chitosan coating was proved by scanning electron microscopy and by fluorescence microscopy. On contact with blood, the chitosan coating led to changes in erythrocyte shape and in their aggregation. The haemostatic activity of the mats increased with increasing chitosan content. Microbiological studies against Staphylococcus aureus revealed that the chitosan coating imparts antibacterial activity to the hybrid mats. The combined haemostatic and antibacterial activities render these novel materials suitable for wound-healing applications.     

Novel electrospun poly(ε-caprolactone)-based bicomponent nanofibers possessing surface enriched in tertiary amino groups

For the first time preparation of electrospun poly(ε-caprolactone) (PCL) based nanofibers possessing surface enriched in tertiary amino groups is shown. For that purpose the pair PCL and poly(ε-caprolactone)-b-poly[(2-dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) diblock copolymers was used. PCL-b-PDMAEMA copolymers were synthesized using a combination of ring-opening polymerization and atom transfer radical polymerization (ATRP). Nanofibers with mean diameters ranging from 400 to 800 nm were obtained. Their morphology was evaluated by scanning electron (SEM) and atomic force microscopy (AFM). It was found that the morphology of the fibers depended on the weight ratio between the partners and the length of the PDMAEMA-block in the copolymers. The enrichment of the fiber surface in tertiary amino groups was studied by X-ray photoelectron spectroscopy (XPS). Increasing the copolymer content and the length of the PDMAEMA-block led to increase of the amount of tertiary amino groups on the fiber surface. The AFM analyses of the mechanical properties of the fiber surface showed that increasing the copolymer content led to decrease of the surface stiffness. The increase of the copolymer content led also to decrease of the melting temperature and the crystallinity degree in respect to PCL from the (co)polymer as determined by differential scanning calorimetry.     

FT-IR microscopy characterization of sol–gel layers prior and after glucose oxidase immobilization for biosensing applications

Micro-Attenuated Total Reflection (ATR) Fourier Transform Infrared spectroscopy was used to investigate sol–gel layers for biosensing applications prior and after glucose oxidase (GOD) immobilization. The changes occurring in sol–gel infrared spectrum after GOD immobilization were clearly evidenced confirming the retaining of the enzyme activity. Moreover, micro-ATR experimental technique allowed us to investigate the spatial distribution of enzyme concentration. The non-destructive nature of our approach also enabled to monitor the time stability of sol–gel layers and of embedded GOD. The temporal evolution of some peaks in infrared spectra of these sol–gel layers was compared with absorption and steady-state fluorescence measurements. The results reported here confirm that micro-ATR infrared spectroscopy can be usefully employed for a non- or minimally invasive detailed characterization of supports for enzyme immobilization.     

Spectrophotometric study of competitive complexation equilibria involving overlapped spectral responding species: Determination of the stability constant of bismuth-pyrophosphate complex

Spectrophotometric study of competitive complex formation equilibria involving overlapped spectral responding species applying a simple and versatile algorithm was carried out. The algorithm involves multivariable regression for calculation of equilibrium concentrations from multiwavelength data and mass action law for the stability constant calculation. The used regression functions are part of common statistical software. Stability constants and complex stoichiometry of competing equilibria were simultaneously determined. The species concentration profiles at several spectral overlapping and ??-coefficient of competing reaction were obtained. Non-absorbing bismuth ?? pyrophosphate (PPh) system was studied as a competitive reaction of bismuth ?? 4-(2-Pyridylazo) resorcinol (PAR) complex. The formation of Bi-PPh complex with 1:1 stoichiometry was proved in the studied concentration region (C_Bi = 1×10^?5 mol L^?1; C_PPh = 5×10^?6 ? 1×10^?4 mol L^?1). The stability constant of the complex at pH 1 and ?? = 1.0 have been determined: log?? = 4.2±0.2.