Properties of polystyrene-poly(methylmethacrylate) random and diblock copolymers in dilute and semidilute solutions

Solution properties for random and diblock copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA) have been measured by dynamic and total intensity light scattering in solvents of differing quality. The results are compared with the corresponding properties for PS and PMMA homopolymers of similar molecular weight, in order to determine if interactions between unlike monomers are significant. The hydrodynamic radius (R_h) and diffusion second virial coefficient (k_d) for the random copolymer are found to be larger than the corresponding values for the homopolymers in a solvent which is near-theta for the two homopolymers, whereas no such effect is observed for the block copolymer. This suggests that most intrachain interactions occur a relatively short distance along the chain backbone. In a mutual good solvent R_h and k_d of the random copolymer are comparable to the average of the values for the homopolymers, indicating that in a good solvent monomer/solvent interactions dominate over monomer/monomer interactions. For an isolated diblock copolymer in a mutual good solvent, there is no evidence that interactions between unlike monomers lead to additional expansion of the entire molecule, as measured by R_h, nor expansion of the individual blocks as probed by light scattering with one block optically masked. However, at low but finite concentration there is evidence (the coefficients of the binary interaction terms in the viscosity and the mutual diffusion coefficient, and the second and third virial coefficients) that a weak ordering effect may exist in block copolymer solutions, far from the conditions where microphase separation occurs. Finally, measurements of ternary polymer-polymer-solvent solutions show no dependence on monomer composition or monomer distribution for the tracer diffusion of probe PS-PMMA copolymers in a PMMA/toluene matrix. This indicate that the frictional interaction is largely unaffected by interactions between unlike monomers. However, there is evidence that the thermodynamic interaction is more unfavorable between a random copolymer and the homopolymer matrix than between a diblock and the matrix. © 1994 John Wiley & Sons, Inc.     

Domain size equilibration in sphere‐forming block copolymers

The kinetics of domain size equilibration were studied for asymmetric poly(ethylene‐alt‐propylene)‐b‐poly(dimethyl siloxane) (EPDMS) and polyisoprene‐b‐poly(dimethyl siloxane) (IDMS) block copolymers in the body‐centered cubic ordered phase. Small‐angle X‐ray scattering measurements of the principal peak position (q*) were made as a function of time after temperature jumps within the ordered state. The equilibration times were remarkably long, especially on cooling and for temperatures below 100 °C. For example, after a quench to 40 °C, q* for EPDMS had not fully equilibrated even after several weeks of annealing; IDMS required several days to equilibrate at the same temperature. In contrast, a lamella‐forming EPDMS sample was able to adjust q* within the timescale of the measurements (i.e., minutes) with both heating and cooling over the same temperature range. Measurements of tracer diffusion indicated that chain mobility was not the rate‐limiting step, although differences in mobility did account for the differences between EPDMS and IDMS. Rather, the limiting step was the required reduction in the number density of spheres on cooling; the disappearance of spheres, either by evaporation or by fusion, provided a large kinetic barrier. Lamellae, however, could adjust domain dimensions simply by local displacements of individual chains. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 715–724, 2003     

The isotropy of Gaussian molecular networks and the stress-birefringence relations for rubberlike materials cross-linked in stressed states

Summary Using the model and some results of theJames andGuth theory of rabberlike elasticity, the relations between stress, birefringence, and strain (measured from the unstressed state) are re-derived by an argument which does not make use of certain assumptions used in previous derivations concerning the isotropy of the distribution of vectors joining junction mean positions and the fixing of junctions in their mean positions. It is proved that in the Gaussian approximation a rubberlike material is necessarily isotropic in the sense that the relations between the stress, strain, and refractive index involve no anisotropic constant tensors. The argument is applicable to networks whose junctions are introduced when the material is in different states of stress, and furnishes strong reasons for regarding the relations between flow birefringence and stress, previously derived on the basis of a network theory for concentrated polymer solutions, as being no longer restricted to solutions of constant viscosity.

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Zusammenfassung Unter Verwendung des Modells und einiger Ergebnisse der Theorie vonJames undGuth für Gummielastizit?t wurden die Beziehungen zwischen Spannung Doppelbrechung und Verformung (gemessen gegen den unbelasteten Zustand) erneut abgeleitet. Es wurde kein Gebrauch gemacht von den in früheren Ableitungen enthaltenen Annahmen über die Fixierung der Bindungen in mittleren Positionen und über die Isotropie der Verteilung der Vektoren, die diese Positionen verbinden. Es wird gezeigt, da? in derGauss-N?herung eines gummiartigen Materials Isotropie in dem Sinne erforderlich ist, da? die Beziehungen zwischen Spannung, Verformung und Brechungsindex keine anisotropen Tensoren der Konstanten enthalten. Diese Ableitung ist anwendbar auf Netzwerke, deren Bindungen eingeführt werden, w?hrend das Material in verschiedenen Spannungszust?nden vorliegt, und liefert eine gute Grundlage für die Annahme, da? die Beziehungen zwischen Str?mungsdoppelbrechung und Spannung, die früher auf Grund der Netzwerktheorie für konzentrierte Polymerenl?sungen abgeleitet wurden, nicht mehr auf L?sungen konstanter Viskosit?t beschr?nkt sind.

     

Development of a liquid chromatographic time-of-flight mass spectrometric method for the determination of unlabelled and deuterium-labelled alpha-tocopherol in blood components

A method is described for the analysis of deuterated and undeuterated alpha-tocopherol in blood components using liquid chromatography coupled to an orthogonal acceleration time-of-flight (TOF) mass spectrometer. Optimal ionisation conditions for undeuterated (d0) and tri- and hexadeuterated (d3 or d6) alpha-tocopherol standards were found with negative ion mode electrospray ionisation. Each species produced an isotopically resolved single ion of exact mass. Calibration curves of pure standards were linear in the range tested (0-1.5 microM, 0-15 pmol injected). For quantification of d0 and d6 in blood components following a standard solvent extraction, a stable-isotope-labelled internal standard (d3-alpha-tocopherol) was employed. To counter matrix ion suppression effects, standard response curves were generated following identical solvent extraction procedures to those of the samples. Within-day and between-day precision were determined for quantification of d0- and d6-labelled alpha-tocopherol in each blood component and both averaged 3-10%. Accuracy was assessed by comparison with a standard high-performance liquid chromatography (HPLC) method, achieving good correlation (r(2) = 0.94), and by spiking with known concentrations of alpha-tocopherol (98% accuracy). Limits of detection and quantification were determined to be 5 and 50 fmol injected, respectively. The assay was used to measure the appearance and disappearance of deuterium-labelled alpha-tocopherol in human blood components following deuterium-labelled (d6) RRR-alpha-tocopheryl acetate ingestion. The new LC/TOFMS method was found to be sensitive, required small sample volumes, was reproducible and robust, and was capable of high throughput when large numbers of samples were generated.     

Dynamics of a poly(ethylene oxide) tracer in a poly(methyl methacrylate) matrix: remarkable decoupling of local and global motions

The tracer diffusion coefficient of unentangled poly(ethylene oxide) (PEO, M=1000 gmol) in a matrix of poly(methyl methacrylate) (PMMA, M=10 000 gmol) has been measured over a temperature range from 125 to 220 degrees C with forced Rayleigh scattering. The dynamic viscosities of blends of two different high molecular weight PEO tracers (M=440 000 and 900 000 gmol) in the same PMMA matrix were also measured at temperatures ranging from 160 to 220 degrees C; failure of time-temperature superposition was observed for these systems. The monomeric friction factors for the PEO tracers were extracted from the diffusion coefficients and the rheological relaxation times using the Rouse model. The friction factors determined by diffusion and rheology were in good agreement, even though the molecular weights of the tracers differed by about three orders of magnitude. The PEO monomeric friction factors were compared with literature data for PEO segmental relaxation times measured directly with NMR. The monomeric friction factors of the PEO tracer in the PMMA matrix were found to be from two to six orders of magnitude greater than anticipated based on direct measurements of segmental dynamics. Additionally, the PEO tracer terminal dynamics are a much stronger function of temperature than the corresponding PEO segmental dynamics. These results indicate that the fastest PEO Rouse mode, inferred from diffusion and rheology, is completely separated from the bond reorientation of PEO detected by NMR. This result is unlike other blend systems in which global and local motions have been compared.     

Specific method for the determination of ozone in the atmosphere

A simple, sensitive and specific method for the determination of ozone in the atmosphere is described. Reactions of ozone with several 1-alkenes were studied at room temperature (25°). Eugenol(4-allyl-2-methoxyphenol), when reacted with ozone, was found to produce relatively large amounts of formaldehyde compared to other 1-alkenes tested. The method described was compared with alkaline iodide method for the determination of various concentrations of ozone in the range 0.05–2.0 p.p.m. Hydrogen peroxide, peracetic acid, sulfur dioxide and various reducing agents commonly present in the air, do not interfere. Formaldehyde when present in the air, must be determined simultaneously and the concentration of formaldehyde subtracted from that of the ozone. Any formaldehyde monitoring equipment can be easily adapted for the determination of ozone.     

Detection of pollen flavonoids by fluorescence on impregnated papers

Summary Limits of detection of some pollen flavonoids are recorded. The flavonoids were detected by aluminum, beryllium, and zirconium ions. Paper chromatography revealed dactylin and isoquercitrin to be present in extracts of orchard grass pollen. Only dactylin was found in timothy pollen extracts.

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Zusammenfassung Die Erfassungsgrenzen der Tüpfelproben einiger Pollenflavone auf mit Aluminium-, Beryllium- und Zirkoniumsalz imprägniertem Papier werden angegeben. Papierchromatographie zeigte die Gegenwart von Dactylin und Isoquercitrin in Extrakten der Pollen vonDactylis glomerata L. an. Pollenextrakt vonPhleum pratense L. enthielt nur Dactylin.

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Résumé Les auteurs indiquent les limites de détection de quelques flavonoïdes de pollen. Les flavonoïdes sont décelés par les ions aluminium, glucinium et zirconium. La Chromatographie sur papier a montré que la dactyline et l'isoquercitine étaient présentes dans les extraits de dactyle. Seule la dactyline a été trouvée dans les extraits de fléole des prés.

     

Micellar shape change and internal segregation induced by chemical modification of a tryptych block copolymer surfactant

We report the detailed characterization of micelles formed by two nonionic, amphiphilic ABC triblock copolymers. Poly(ethylene oxide)-b-poly(styrene)-b-1,2-poly(butadiene) (PEO-b-PS-b-PB) triblock copolymer "OSB" forms core-corona spherical micelles in aqueous solution, and the two hydrophobic blocks S and B are mixed homogeneously within the micelle core. PEO-b-PS-b-PB:C6F13I triblock copolymer "OSF" was prepared by selective fluorination of the B block in OSB with n-perfluorohexyl iodide. Fluorination of the B block induces internal segregation into an inner F core and an intermediate S shell. Furthermore, the strong incompatibility that results from fluorination drives a shape change into an oblate ellipsoid. These micellar morphologies are confirmed by combined light, neutron, and X-ray scattering measurements, as well as TEM imaging.