Investigation of copolymers of styrene and ethyl methacrylate by size exclusion chromatography and gradient HPLC

Summary Copolymers of styrene and ethyl methacrylate have been separated according to composition by gradient HPLC on silica columns or CN bonded phase columns. This mode of separation according to composition was applied to fractions obtained by size exclusion chromatography (SEC). From viscosity and molecular mass data of copolymers with a styrene content ranging from 7.5 to 95.3 mass-% it can be concluded that SEC separates mainly by molecular mass even in this copolymer system. Thus, chromatographic cross-fractionation is possible by prefractionation by SEC and subsequent separation according to composition by gradient HPLC.

---

Untersuchung von Copolymeren von Styrol und Ethylmethacrylat durch Ausschluß-Chromatographie und Gradienten-HPLC

     

Polymerization of methyl methacrylate up to high degrees of conversion: Experimental investigation of the diffusion-controlled polymerization

The kinetic model given by Marten and Hamielec that describes the bulk polymerization of methyl methacrylate (MMA) and accounts for diffusion-controlled termination and propagation was modified to include termination by combination and reaction diffusion and was then tested using isothermal conversion/time and molecular weight data obtained dilatometrically at various temperatures and with three different initiators. For each series of measurements two adjustable parameters were fitted to the conversion/time data. Excellent fits were obtained and the adjustable parameters were found to be the same for all concentration levels of the three initiators and to vary in a simple manner with temperature. The predicted molecular weight averages and molecular weight distributions were in satisfactory agreement with those found experimentally considering the difficulty of measuring high molecular weight PMMA by GPC. This model thus satisfies the specifications for a polymer reactor model that can be used to optimize commercial production systems.     

Herstellung und Eigenschaften von Au2P3 und seine Identifizierung in diffundierten Si-Scheiben

Zusammenfassung In Au-diffundierten, Phosphor-dotierten Si-Scheiben wurden durch Transmissionselektronenmikroskopie feine Ausscheidungsteilchen beobachtet, von denen angenommen wurde, daß sie aus einer Au–P-Verbindung bestehen. Um die für eine Identifizierung dieser Ausscheidung mittels Elektronenbeugung notwendigen Daten der Kristallstruktur zu eihalten, wurde eine geringe Menge von Au₂P₃-Einkristallen durch eine Gasphasentransportreaktion der Elemente hergestellt. Die erhaltenen Kristalle wurden chemisch und durch Röntgenbeugung untersucht. Weiters wurden Aussagen über die Morphologie und die Stabilität der Au₂P₃-Kristalle erhalten.

---

Formation and properties ofAu ₂ P ₃ and its identification in diffusedSi-wafers

Fine precipitate particles assumed to consist of a Au–P compound were observed by transmission electron microscopy in Au-diffused phosphorus-doped Si-wafers. To obtain crystal structure data required for an electron diffraction identification of this precipitate, a small amount of Au₂P₃ single crystals was grown from the elements by a vapor transport method and analyzed by chemical and X-ray diffraction methods. In addition, information on the morphology and stability of Au₂P₃ crystals was obtained.

---

---

Mit 5 Abbildungen

---

Herrn Prof. Dr.Hans Nowotny gewidmet.

---

Teilweise bei der Annual Pittsburgh Diffraction Conference in Pittsburgh im November 1965 vorgetragen.     

The thermal response of a metal slab to a class of radially dependent heat inputs

Summary The temperature fields are deduced for an infinite metal slab of finite thickness produced by a heat flux input which depends on the radial coordinate. The formal solution is obtained by means of transform techniques.Several representations of the Green's function are obtained as well as two approximate representations. One of these approximations converges well for time large the other for time small.A small time asymptotic expansion is given for input flux densities which satisfy certain smoothness requirements.Two inputs have been considered in detail. One is the uniform spot and the other is the Gaussian. An extension of the results obtained by Oosterkamp³) has been obtained along with an estimate of the validity.The work reported in this paper was supported in part by Contract AF 30(602)-2305 between The Ohio State University Research Foundation and Rome Air Development Center, Griffiss Air Force Base, New York.     

Size exclusion chromatography of cationic polyelectrolytes

Molecular weight distributions of the cationic polyelectrolyte poly(2-trimethylammonium ethyl methacrylate chloride) were determined via size exclusion chromatography (SEC) for a very broad molecular weight range ($\text{7.7 × 10}{}^3\text{?}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{? 1.1 × 10}{}_7$). Non-size exclusion effects (ion inclusion, ion exclusion, adsorption) were controlled by special surface treatment of the stationary phase (DMAE-Fractosil^R, E. Merck) and by proper selection of the mobile phase. A non-linear effective molecular weight calibration procedure was applied to account for the high polydispersity of the polyelectrolyte standard polymers. $\text{M}{}_{\mathrm{w}}$ data from SEC experiments agree with results from light scattering, and the molecular weight distributions obtained from SEC and sedimentation velocity analysis compare well.     

Investigation of copolymers of styrene and ethyl methacrylate by size-exclusion chromatography and gradient HPLC

Summary Copolymers of styrene and ethyl methacrylate (SEMA) have been separated according to composition by reversed-phase chromatography on C18 columns. The starting eluent was methanol, in which the copolymers are insoluble, and an elution gradient was formed by the addition of tetrahydrofuran, which is less polar than methanol yet a good solvent for SEMA copolymers. The method was applied to fractions obtained by size exclusion chromatography of model mixtures, and yielded a separation superior to that obtained in normal-phase mode on polar columns using gradients of increasing polarity.

---

Untersuchung von Copolymeren von Styrol und Ethylmethacrylat durch Größenausschluß-Chromatographie und Gradient-HPLCII. Gradient-HPLC unter Umkehrphasen-Bedingungen

---

Part I: see [1]     

Persistency of linear programming relaxations for the stable set problem

The Nemhauser–Trotter theorem states that the standard linear programming (LP) formulation for the stable set problem has a remarkable property, also known as (weak) persistency: for every optimal LP solution that assigns integer values to some variables, there exists an optimal integer solution in which these variables retain the same values. While the standard LP is defined by only non-negativity and edge constraints, a variety of other LP formulations have been studied and one may wonder whether any of them has this property as well. We show that any other formulation that satisfies mild conditions cannot have the persistency property on all graphs, unless it is always equal to the stable set polytope.