ROLE OF CHLORINE AND ALKALI PROMOTERS IN ETHYLENE EPOXIDATION OVER SINGLE CRYSTAL SILVER SURFACES.

Experiments with N//2O were carried out with a view to obtaining additional information about the reactivity of oxygen surface species. On clean Ag, N//2O decomposition was found to be an activated process which led exclusively to the deposition of O(a) species. The presence of preadsorbed oxygen or subsurface oxygen served to enhance the deposition rate of O(a). Subsequent dosing with ethylene at 300 K of such an oxygen-populated surface followed by TPR examination showed it to be active for ethylene oxide formation. Control experiments established that adventitious decomposition of N//2O at the reactor walls or specimen supports followed by possible re-absorption of O//2(a) was an entirely negligible process. ) The oxidation activity of N//2O was also investigated at elevated pressures in the batch reactor.

Mechanism And Selectivity In The Epoxidation Of Ethylene Over Silver: The Results Of Single Crystal Measurements

The silver-catalysed oxidation of ethylene has been examined on the (III) face of a single crystal by a combination of electron spectroscopy and kinetic measurements at pressures of up to 50 Torr. The necessary and sufficient conditions for ethylene oxide formation are established, reaction intermediates are identified, kinetic isotope effects are observed and the role of Cs in modifying reaction selectivity is examined. It is shown that surface alkali exhibits opposite effects on the reactions which lead to the further oxidation of ethylene oxide and on the direct combustion of ethylene. © 1984.

Probing the micellization of diblock and triblock copolymers of poly(L-lactide) and poly(ethylene glycol) in aqueous and NaCl salt solutions

The micelle formation of a series of amphiphilic block copolymers in aqueous and NaCl solutions was studied by a fluorescent probe technique using pyrene as a 'model drug'. These copolymers were synthesized from poly (ethylene glycol) (PEG) and L-lactide by a new calcium ammoniate catalyst. They had fixed PEG block lengths (44, 104 or 113 ethylene oxide units) and various poly(L-lactide) (PLLA) block lengths (15-280 lactide units). The critical micelle concentration (cmc) was found to decrease with increasing PLLA content. The distinct dissimilarity of the cmc values of diblock and triblock copolymers based on the same block length of PEG provided evidence for the different configurations of their micelles. It was also observed that the introduction of NaCl salt significantly contributed to a decrease in the cmcs of the copolymers with short PEG and PLLA blocks, while it had less influence on the cmcs of copolymers with long PEG or PLLA blocks. The dependence of partition coefficients ranging from 0.2x10(5) to 1.9x10(5) on the PLLA content in the copolymer and on the micelle configuration was also discussed.

Liquid-liquid phase behavior of toluene/polyethylene oxide/poly(ethyleneoxide-b-dimethylsiloxane) polymer-containing ternary mixtures

The experimental data of phase diagrams for both polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) binary and toluene/polyethylene oxide/poly(ethylene oxide-b-dimethylsiloxane) ternary polymer-containing systems was obtained at atmosphere pressure by light scattering method. The critical points for some pre-selected compositions and the pressure effect on the phase transition behavior of ternary system were investigated by turbidity measurements. The chosen system is a mixture of ternary which is one of the very few abnormal polymer-containing systems exhibiting pressure-induced both miscibility and immiscibility. This unusual behavior is related to the toluene concentration in the mixtures. The effect of toluene on the phase transition behavior of the ternary polymer-containing mixture was traced. Such behavior can make it possible to process composite materials from incompatible polymers.

Poly(ethylene glycol)-block-poly(butyl acrylate). II. Characterization and properties

Poly(ethylene glycol)-block-poly(butyl acrylate) synthesized by radical polymerization in a one-step procedure were characterized by gel permeation chromatography, infrared, IH-NMR spectroscopy, and differential scanning calorimetry (DSC). The crystalline property, emulsifying property, and phase transfer catalytic effect in the Williamson reaction were studied. It was found that the crystallinity of the copolymer increased with an increase in both the content and molecular weight of poly( ethylene oxide) (PEO) sequences. DSC curves showed two distinct crystallization temperature due to the heterogeneous nucleation and homogeneous nucleation crystallization. The casting solvent significantly affected the morphology and crystallinity of the solvent cast films. Both the emulsifying volume and the phase transfer catalytic efficiency in the Williamson reaction increased with the amount and PEO content of the block copolymers used, but decreased with an increase in the molecular weight of PEO sequences. (C) 1998 John Wiley & Sons, Inc.

Poly(ethylene glycol) block poly(butyl acrylate) .1. Synthesis

Prepolymers of poly(ethylene oxide) (Pre-PEG) were synthesized by reacting azoisobutyronitrile (AIBN) with poly(ethylene glycol) (PEG), and their structures were characterized by IR and UV. The molecular weight of pre-PEG was related to the feed ratio and reaction time. These prepolymers can be used to prepare block copolymers - poly(ethylene oxide)-block-poly(butyl acrylate) (PEO-b-PBA) by radical polymerization in the presence of butyl acrylate (BA). Solution polymerization was a suitable technique for this step. The yield and the molecular weight of the product were related to the ratio of the prepolymer to BA, the reaction time, and temperature. GPC showed that the molecular weight increased with a higher ratio of BA to pre-PEO. The intrinsic viscosity of the copolymers was only slightly dependent on reaction time, but decreased at higher reaction temperatures, as did the amount of PEA homopolymer. (C) 1997 John Wiley & Sons, Inc.

Study of ion solvation and ion association in polymer gel electrolyte with polyethylene oxide-co-polypropylene oxide as a plasticizer

Using a molal conductance method, ion solvation and ion association in polytriethylene glycol dimethacrylate (PTREGD)-LiClO4 gel electrolytes with amorphous ethylene oxide-co-propylene oxide (EO-co-PO, <(M)over bar (n)>, = 1750) as the plasticizer were investigated. It was found that the fraction of solute existing as single ions (alpha(i)) and ion pairs (alpha(p)) decreases, while that of triple ions (alpha(t)) increases linearly with increasing salt concentration. The dependence of these fractions on molecular weight of plasticizer was also examined. It was shown that alpha(i) and alpha(t) increase and alpha(p) decreases with increasing molecular weight. The result of temperature dependence of these fractions was very interesting: when the temperature is lower than 55 degrees C, alpha(i) increases while alpha(p) and alpha(t) decrease with increasing temperature; however, when the temperature is higher than 55 degrees C, the reverse is true.

Association Behavior of Biotinylated and Non-Biotinylated PolyEthylene Oxide-b-Poly(2-(Diethylamino)Ethyl Methacrylate)

Biotinylated and non-biotinylated copolymers of ethylene oxide (EO) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were synthesized by the atom transfer radical polymerization technique (ATRP). The chemical compositions of the copolymers as determined by NMR are represented by PEO₁₁₃PDEAEMA₇₀ and biotin-PEO₁₀₄PDEAEMA₉₃ respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (Rh) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with Rh of about 6-7 nm. However, at a physiological salt concentration (cs) of about 0.16M NaCl and a pH of 7-8, the copolymers form large loosely packed Guassian chains, which were not present at the low cs of 0.001M NaCl. The critical micelle concentrations (CMC) and the cytotoxicity of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical CMC values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05mg/g (> 83% cell survival at this concentration).

NMR study of ion-conducting organic-inorganic nanocomposites poly(ethylene glycol) - Silica - LiClO4

Hybrid organic-inorganic ionic conductors, also called ormolytes, were obtained by dissolution of LiClO4 into silica/poly(ethylene glycol) matrices. Solid-state nuclear magnetic resonance (NMR) was used to probe the inorganic phase structure (Si-29) and the effects of the temperature and composition on the dynamic behavior of the ionic species (Li-7) and the polymer chains (H-1 and C-13). The NMR results between -100 and +90 degrees C show a strong correlation with ionic conductivity and differential scanning calorimetry experiments. The results also demonstrate that the cation mobility is assisted by segmental motion of the polymer, which is in agreement with the results previously reported for pure poly(ethylene oxide), PEG, electrolytes.

Expanding the scope of poly(ethylene glycol)s for bioconjugation to squaric acid-mediated PEGylation and pH-sensitivity

Poly(ethylene glycol) (PEG) is used in a broad range of applications due to its unique combination of properties and is approved use in formulations for body-care products, edibles and medicine. This thesis aims at the synthesis and characterization of novel heterofunctional PEG structures and the establishment of diethyl squarate as a suitable linker for the covalent attachment to proteins. Chapter 1 is an introduction on the properties and applications of PEG as well as the fascinating chemistry of squaric acid derivatives. In Chapter 1.1, the synthesis and properties of PEG are described, and the versatile applications of PEG derivatives in everyday products are emphasized with a focus on PEG-based pharmaceuticals and nonionic surfactants. This chapter is written in German, as it was published in the German Journal Chemie in unserer Zeit. Chapter 1.2 deals with PEGs major drawbacks, its non-biodegradability, which impedes parenteral administration of PEG conjugates with polyethers exceeding the renal excretion limit, although these would improve blood circulation times and passive tumor targeting. This section gives a comprehensive overview of the cleavable groups that have been implemented in the polyether backbone to tackle this issue as well as the synthetic strategies employed to accomplish this task. Chapter 1.3 briefly summarizes the chemical properties of alkyl squarates and the advantages in protein conjugation chemistry that can be taken from its use as a coupling agent. In Chapter 2, the application of diethyl squarate as a coupling agent in the PEGylation of proteins is illustrated. Chapter 2.1 describes the straightforward synthesis and characterization of squaric acid ethyl ester amido PEGs with terminal hydroxyl functions or methoxy groups. The reactivity and selectivity of theses activated PEGs are explored in kinetic studies on the reactions with different lysine and other amino acid derivatives, followed by 1H NMR spectroscopy. Further, the efficient attachment of the novel PEGs to a model protein, i.e., bovine serum albumin (BSA), demonstrates the usefulness of the new linker for the PEGylation with heterofunctional PEGs. In Chapter 2.3 initial studies on the biocompatibility of polyether/BSA conjugates synthesized by the squaric acid mediated PEGylation are presented. No cytotoxic effects on human umbilical vein endothelial cells exposed to various concentrations of the conjugates were observed in a WST-1 assay. A cell adhesion molecule - enzyme immunosorbent assay did not reveal the expression of E-selectin or ICAM-1, cell adhesion molecules involved in inflammation processes. The focus of Chapter 3 lies on the syntheses of novel heterofunctional PEG structures which are suitable candidates for the squaric acid mediated PEGylation and exhibit superior features compared to established PEGs applied in bioconjugation. Chapter 3.1 describes the synthetic route to well-defined, linear heterobifunctional PEGs carrying a single acid-sensitive moiety either at the initiation site or at a tunable position in the polyether backbone. A universal concept for the implementation of acetal moieties into initiators for the anionic ring-opening polymerization (AROP) of epoxides is presented and proven to grant access to the degradable PEG structures aimed at. The hydrolysis of the heterofunctional PEG with the acetal moiety at the initiating site is followed by 1H NMR spectroscopy in deuterium oxide at different pH. In an exploratory study, the same polymer is attached to BSA via the squarate acid coupling and subsequently cleaved from the conjugate under acidic conditions. Furthermore, the concept for the generation of acetal-modified AROP initiators is demonstrated to be suitable for cholesterol, and the respective amphiphilic cholesteryl-PEG is cleaved at lowered pH. In Chapter 3.2, the straightforward synthesis of α-amino ω2-dihydroxyl star-shaped three-arm PEGs is described. To assure a symmetric length of the hydroxyl-terminated PEG arms, a novel AROP initiator is presented, who’s primary and secondary hydroxyl groups are separated by an acetal moiety. Upon polymerization of ethylene oxide for these functionalities and subsequent cleavage of the acid-labile unit no difference in the degree of polymerization is seen for both polyether fragments.

Poly(hydroxyether of phenolphthalein) and its blends with poly(ethylene oxid)

Poly(hydroxyether of phenolphthalein) (PPH) was synthesized through the polycondensation of phenolphthalein with epichlorohydrin. It was characterized by Fourier transform infrared (FTIR) spectroscopy, NMR spectroscopy, and differential scanning calorimetry (DSC). The miscibility of the blends of PPH with poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. DSC showed that the PPH/PEO blends prepared via casting from N,N-dimethylformamide possessed single, composition-dependent glass-transition temperatures. Therefore, the blends were miscible in the amorphous state for all compositions. FTIR studies indicated that there were competitive hydrogen-bonding interactions with the addition of PEO to the system, which were involved with (OHO)-O-. . .=C

Growth of boehmite nanofibers by assembling nanoparticles with surfactant micelles

It is known that boehmite (AlOOH) nanofibers formed in the presence of nonionic poly(ethylene oxide) (PEO) surfactant at 373 K. A novel approach is proposed in this study for the growth of the boehmite nanofibers: when fresh aluminum hydrate precipitate was added at regular interval to initial mixture of boehmite and PEO surfactant at 373 K, the nanofibers grow from 40 to 50 nm long to over 100 nm. It is believed that the surfactant micelles play an important role in the nanofiber growth: directing the assembly of aluminum hydrate particles through hydrogen bonding with the hydroxyls on the surface of aluminum hydrate particles. Meanwhile a gradual improvement in the crystallinity of the fibers during growth is observed and attributed to the Ostwald ripening process. This approach allows us to precisely control the size and morphology of boehmite nanofibers using soft chemical methods and could be useful for low temperature, aqueous syntheses of other oxide nanomaterials with tailorable structural specificity such as size, dimension and morphology.

Combining electrospun scaffolds with electrosprayed hydrogels leads to three-dimensional cellularization of hybrid constructs

A common problem in the design of tissue engineered scaffolds using electrospun scaffolds is the poor cellular infiltration into the structure. To tackle this issue, three approaches to scaffold design using electrospinning were investigated: selective leaching of a water-soluble fiber phase (poly ethylene oxide (PEO) or gelatin), the use of micron-sized fibers as the scaffold, and a combination of micron-sized fibers with codeposition of a hyaluronic acid-derivative hydrogel, Heprasil. These designs were achieved by modifying a conventional electrospinning system with two charged capillaries and a rotating mandrel collector. Three types of scaffolds were fabricated: medical grade poly(epsilon-caprolactone)/collagen (mPCL/Col) cospun with PEO or gelatin, mPCL/Col meshes with micron-sized fibers, and mPCL/Col microfibers cosprayed with Heprasil. All three scaffold types supported attachment and proliferation of human fetal osteoblasts. However, selective leaching only marginally improved cellular infiltration when compared to meshes obtained by conventional electrospinning. Better cell penetration was seen in mPCL/Col microfibers, and this effect was more pronounced when Heprasil regions were present in the structure. Thus, such techniques could be further exploited for the design of cell permeable fibrous meshes for tissue engineering applications.

Formation of nanoporous materials via mild retro-Diels–Alder chemistry

Poly(styrene)-block-poly(ethylene oxide) copolymers synthesized via the combination of reversible addition fragmentation chain transfer (RAFT) polymerization and hetero Diels–Alder (HDA) cycloaddition can be cleaved in the solid state by a retro-HDA reaction occurring at 90 °C. Nanoporous films can be prepared from these polymers using a simple heating and washing procedure.