Synthesis,characterization, and polymerization activity of [bis(4,4'-bis(neophyldimethylsilylmethyl)-2,2'-bipyridyl)copper(I)]+CuBr2- and Implications for copper(I) catalyst structures in atom transfer radical polymerization

A series of 4,4'-disilyl-substituted-2,2'-bipyridine ligands were prepared using a metathesis reaction of the dianion of 4,4'-dimethyl-2,2'-bipyridine with several trialkylsilyl chlorides: 4,4'bis(tert-butyldimethylsilylmethyl)-2,2'-bipyridine (dTBDMSbipy), 4,4'-bis(dimethylthexylsilylmethyl)-2,2'-bipyridine (dTHEXbipy), and 4,4'-bis(neophyldimethylsilylmethyl)-2-2'-bipyridine (dNEObipy). It was observed that the side chain length correlated with the ability of the ligand to form hydrocarbon soluble complexes of copper(I) bromide, with dNEObipy forming the most soluble and easily crystallized complexes. The atom transfer radical polymerization (ATRP) of styrene using dNEObipy as the ligand displayed molecular weight control equivalent to other ATRP systems in which solubilizing ligands, such as 4,4'-di-5-nonyl-2,2'-bipyridine or 4,4'-di-n-heptyl-2,2'-bipyridine, were used. The one-to-one complex of dNEObipy with CuBr was prepared and its crystal structure was determined. The resulting complex had the ionic formulation [(dNEObipy)2Cu]+[CuBr2]- and displayed similar activities in styrene ATRP as the standard 2 dNEObipy/CuBr catalyst system. These and other polymerization results in addition to NMR experiments suggest that the predominant copper(I) species formed in ATRP solutions is the 2-to-1 ligand-to-copper(I) cation, [(dNEObipy)2Cu]+, with either a dihalocuprate or halide counteranion, depending upon the conditions.     

Collocation Methods for Weakly Singular Second-kind Volterra Integral Equations with Non-smooth Solution

Collocation type methods are studied for the numerical solutionof the weakly singular Volterra integral equation of the secondkind: where the solution (t) is assumedto have the form f(t) = x(t)+r^?(t), x and being sufficientlysmooth. The solution is approximated near zero by a linear combinationof powers of t?, and away from zero by the usual polynomialrepresentation. Convergence is proved and many numerical experimentsare carried out with examples from the literature. A comparisonis made with a method of Brunner & Norsett (1981), originallydeveloped for (1) with a smooth solution. Special attentionis paid to the numerical approximation of the so-called momentintegrals which emerge in the collocation scheme.     

Versatile Organometallic Initiators for the Living Polymerization of Isocyanates

Shashoua and Sweeney first demonstrated that isocyanates could by polymerized via an anionic mechanism to form high molecular weight materials. We have sought to eliminate the problems associated with the anionic procedure by developing transition metal complexes which are capable of catalyzing the living polymerization of isocyanates. Recently, we reported the living polymerization of alkyl isocyanates using TiCl₃OCH₂CF₃, I. Using I, polyisocyanates with controlled molecular weights and narrow polydispersities can be obtained at room temperature. ε⁵-CpTiCl₂N(CH₃)₂ (Cp = cyclopentadienyl), III, is also an excellent catalyst for the polymerization of isocyanates, and in terms of ease of handling and purification and tolerance toward monomer functionality, superior to I. In order to prepare triblock copolymers containing amorphous segments sandwiched between two isocyanate segments, we have prepared bimetallic initiators comprised of titanium alkoxides con- nected by flexible linkers. These linkers may be a small molecule (1,4- dihydroxycyclohexane, V) or a polymer (polydimethylsiloxane, PDMS, VI). Complexes V and VI can be used to initiate the living polymerization of isocyanates to yield polymers possessing central cyclohexyl bends (ldquo;broken worms rdquo;) or PDMS segments (triblock copolymers), respectively. Finally, cyclopolymerizations of 1,2-diisocyanates using these or- ganometallic initiators are reported.     

A stripe-to-droplet transition driven by conformational transitions in a binary lipid-lipopolymer mixture at the air-water interface

We report the observation of an unusual stripe-droplet transition in precompressed Langmuir monolayers consisting of mixtures of poly(ethylene) glycol (PEG) amphiphiles and phospholipids. This highly reproducible and fully reversible transition occurs at approximately zero surface pressure during expansion (or compression) of the monolayer following initial compression into a two-dimensional solid phase. It is characterized by spontaneous emergence of an extended, disordered stripe-like morphology from an optically homogeneous phase during gradual expansion. These stripe patterns appear as a transient feature and continuously progress, involving gradual coarsening and ultimate transformation into a droplet morphology upon further expansion. Furthermore, varying relative concentrations of the two amphiphiles and utilizing amphiphiles with considerably longer ethylene glycol headgroups reveal that this pattern evolution occurs in narrow concentration regimes, values of which depend on ethylene oxide headgroup size. These morphological transitions are reminiscent of those seen during a passage through a critical point by variations in thermodynamic parameters (e.g., temperature or pressure) as well as those involving spinodal decomposition. While the precise mechanism cannot be ascertained using present experiments alone, our observations can be reconciled in terms of modulations in competing interactions prompted by the pancake-mushroom-brush conformational transitions of the ethylene glycol headgroup. This in turn suggests that the conformational degree of freedom represents an independent order parameter, or a switch, which can induce large-scale structural reorganization in amphiphilic monolayers. Because molecular conformational changes are pervasive in biological membranes, we speculate that such conformational transition-induced pattern evolution might provide a physical mechanism by which membrane processes are amplified.     

Bestimmung des Nitrations und des Nitritions

Ohne Zusammenfassung     

Identification of acidic phosphorus-containing ligands involved in the surface chemistry of CdSe nanoparticles prepared in tri-N-octylphosphine oxide solvents

The surface ligand composition of CdSe nanoparticles prepared using technical grade tri-n-octylphosphine oxide (TOPO) was investigated using a nucleophilic ligand displacement methodology and (31)P {(1)H} NMR spectroscopy. 4-(N,N-Dimethylamino)pyridine (DMAP) and benzyltrimethylammonium propionate were added to tetrahydrofuran solutions of CdSe nanoparticles prepared in technical grade TOPO. DMAP was shown to be a sufficiently strong nucleophile to displace the more weakly coordinating ligands, TOPO, TOPSe, di-n-octylphosphinate, and n-octylphosphonate (OPA). Benzyltrimethylammonium propionate was shown to be a stronger nucleophile than DMAP in that it could displace all the aforementioned surface-bound ligands as well as a previously unidentified surface-bound phosphorus species. Independent synthesis and (31)P {(1)H} NMR spectral matching confirmed that the new species was P,P'-(di-n-octyl) dihydrogen pyrophosphonic acid (PPA). The PPA was shown to form during the nanoparticle synthesis via the dehydrative condensation of OPA. CdSe nanoparticle syntheses were performed using pure TOPO and added OPA, and subsequent displacement experiments showed that OPA and PPA were the predominant surface-bound ligands. CdSe nanoparticle syntheses were performed using pure TOPO and added PPA, and subsequent displacement experiments showed that PPA was the predominant surface-bound ligand. PPA was also shown to have the greatest affinity for the nanoparticle surface of all the ligands investigated. Thus, a model for the surface ligand composition could be developed for nanoparticles prepared using technical grade TOPO or other high-boiling solvents with added acidic phosphorus compounds.     

无机酸洗脱对胜利褐煤微晶结构及其自燃倾向性的影响

利用XRD、Raman、XPS和FT-IR表征技术,研究无机酸洗脱(HCl、H2SO4、HCl-HF)处理的胜利褐煤微晶结构的变化,采用自行设计的表面吸附仪-GC联用装置,对样品进行不同温度的低温脉冲氧化实验,考察了煤样在不同温度下氧吸附量的变化规律,通过低温脉冲氧吸附规律与TG/DTG和固定床燃烧实验关联,考察了煤样的自燃倾向。结果表明,无机酸洗脱对矿物质的脱除使得煤结构的有序度增加,石墨化程度提高,无机酸洗脱煤样与原煤相比吸氧量明显下降。随着吸附温度的升高,各煤样吸氧量明显增加,且随着脱除矿物质程度的增加,吸氧量呈减小的趋势,导致自燃倾向降低。     

Simultaneous spectrophotometric flow-through measurements of pH, carbon dioxide fugacity, and total inorganic carbon in seawater

An autonomous multi-parameter flow-through CO₂ system has been developed to simultaneously measure surface seawater pH, carbon dioxide fugacity (fCO₂), and total dissolved inorganic carbon (DIC). All three measurements are based on spectrophotometric determinations of solution pH at multiple wavelengths using sulfonephthalein indicators. The pH optical cell is machined from a PEEK polymer rod bearing a bore-hole with an optical pathlength of ∼15 cm. The fCO₂ optical cell consists of Teflon AF 2400 (DuPont) capillary tubing sealed within the bore-hole of a PEEK rod. This Teflon AF tubing is filled with a standard indicator solution with a fixed total alkalinity, and forms a liquid core waveguide (LCW). The LCW functions as both a long pathlength (∼15 cm) optical cell and a membrane that equilibrates the internal standard solution with external seawater. fCO₂ is then determined by measuring the pH of the internal solution. DIC is measured by determining the pH of standard internal solutions in equilibrium with seawater that has been acidified to convert all forms of DIC to CO₂. The system runs repetitive measurement cycles with a sampling frequency of ∼7 samples (21 measurements) per hour. The system was used for underway measurements of sea surface pH, fCO₂, and DIC during the CLIVAR/CO₂ A16S cruise in the South Atlantic Ocean in 2005. The field precisions were evaluated to be 0.0008 units for pH, 0.9 μatm for fCO₂, and 2.4 μmol kg⁻¹ for DIC. These field precisions are close to those obtained in the laboratory. Direct comparison of our measurements and measurements obtained using established standard methods revealed that the system achieved field agreements of 0.0012 ± 0.0042 units for pH, 1.0 ± 2.5 μatm for fCO₂, and 2.2 ± 6.0 μmol kg⁻¹ for DIC. This system integrates spectrophotometric measurements of multiple CO₂ parameters into a single package suitable for observations of both seawater and freshwater.     

XPS characterisation of core-shell silica-polymer composite particles synthesised by atom transfer radical polymerisation in aqueous media

Near-monodisperse, siloxane-functionalised silica particles are used as a colloidal substrate for the surface-initiated polymerisation of various hydrophilic methacrylates: oligo(ethylene glycol) methacrylate (OEGMA), 2-(N-morpholino)ethyl methacrylate (MEMA), and ammonium 2-sulfatoethyl methacrylate (SEM) by atom transfer radical polymerisation in aqueous media at room temperature. The bulk and surface compositions of the resulting composite particles were assessed using various techniques. Thermogravimetric analysis of the resulting silica-polymer composites indicated polymer loadings of 5.4-8.6%, depending on the nature, structure and target degree of polymerisation (D_p). Dynamic light scattering studies indicate increases in hydrodynamic diameter of 14-87 nm compared to the reference silica particles. FT-IR spectroscopy confirmed additional features characteristic of the carbonyl group and pendant end-chain functionalities of the methacrylic polymer chains. The elemental and chemical surface compositions of the initial silica particles and final polymer-grafted composite particles were extensively investigated by X-ray photoelectron spectroscopy (XPS). The composite particles had appreciably higher C/Si atomic ratios, compared to the original initiator-functionalised silica particles, and these ratios increased with increasing target D_p. In addition, close inspection revealed that the relative intensities of the various components of the peak-fitted C1s envelopes varied significantly, depending on the target degree of polymerisation and the chemical structure of the methacrylic monomer. Moreover, in the case of the MEMA and SEM polymerisations, new nitrogen (MEMA) and sulfur (SEM) XPS signals were detected. This XPS study confirmed the presence of a thin outer layer of grafted polymer chains surrounding the silica particles.