Dielectric spectra of composites of poly(ethylene oxide), PEO, in polystyrene, PS, have been obtained, as a function of frequency and temperature. The dispersion of a high-dielectric constant, ...low-glass transition temperature, semicrystalline polymer (PEO) in an amorphous, lower dielectric constant, high-T g continuum (PS) has enabled the dielectric observation of four molecular relaxation processes in PEO. They are the α relaxation associated with the crystalline melt of PEO; two WLF type relaxations, β and β‘, which we speculate to be respectively associated with the onset of segmental motion and free-volume expansion of unrestricted amorphous PEO chains and with amorphous PEO chain segments tethered in crystallites; and a sub-T g, γ relaxation associated with localized motions in the crystalline chain segments. The relaxations associated with the α and β‘ processes have not been previously observed dielectrically. In pure, neat PEO, the α and β‘ relaxations are obscured by dc losses. The dispersion of PEO as micron-sized and submicron phases in PS enables its full relaxation spectrum to be observed.
In the present study, a neutral crown ether dye (NCED), 4-Nitrophenyl)(4-(4,7,10,13,16-pantaoxa-1 azacyclooctadecyl)phenyl diazen and an ionic crown ether dye (ICED), ...1-Methyl-{2-4-(4,7,10,13,16-pentaoxa-1 azacyclooctadecyl)phenylethenyl}pyridinium-iodide were synthesized and immobilized on sulfonated hydrocarbon-based block copolymer ionomer to determine Ba
2+
and Cu
2+
ions in aqueous solution. 5.0×10
−2
M ion solutions were used since the best absorbance increase was obtained with this concentration. The increases in absorbances after treating the NCED-immobilized thick polymer membranes (0.20 mm thickness) with Ba
2+
and Cu
2+
solutions were 0.1488 and 0.2446 in 120 minutes, respectively. The absorbance increases were 0.1664 and 0.3710 during the same time-interval with ICED-immobilized membranes.
The response time decreased and absorbance values increased when thin polymer membranes (0.04 mm thickness) were used. The absorbance increases were 0.5088 and 0.8761, respectively in one minute with the ICED-immobilized thin membranes. These results are in agreement with shrinking in polymer dimensions. Dye-immobilized polymeric membranes can be used as sensors practically for both of the ions but sensitivity is higher towards Cu
2+
ions.
Four-arm, poly(methyl methacrylate) star polymers having cyclic siloxane cores were prepared by group-transfer polymerization (GTP). In this core-first approach, a cyclic hydromethylsiloxane tetramer ...was hydrosilated with a terminal olefin bearing a silyl ketene acetal, and methyl methacrylate polymerization was initiated in THF using acetate ion as a catalyst. Star polymers having between 20-150 methyl methacrylate repeat units per arm were prepared, and had polydispersities of approx 1.2-1.3, as determined by gel permeation chromatography (GPC). The polymerizations were quantitative. The star topology was confirmed by cleavage of the cyclic siloxane cores with triflic acid in the presence of an excess of hexamethyldisiloxane. The number-average molecular weights of the resulting arms were determined relatively by GPC with PMMA standards and absolutely by end group analysis via exp 1 H NMR of the heptamethyltrisiloxane termini. The results are in reasonable agreement with the predicted arm molecular weights based on the ratios of methyl methacrylate to silyl ketene acetal employed during synthesis.
We report the development of a one-semester lecture and laboratory course in inorganic chemistry that focuses on industrially relevant topics. It provides the students—both chemistry and chemical ...engineering majors—with a realistic perspective and appreciation for this important branch of chemistry and chemical technology, thus better preparing them for future careers in industry. We summarize the topics considered in the lecture part of the course, the learning objectives and organization of the course, and the underlying teaching philosophy. A summary of the associated laboratory, which both illustrates and complements the lecture topics, is included. The course is team-taught by faculty from chemistry and chemical engineering. We found this partnership to represent a great strength, since fundamental issues of chemistry (bonding, reactivity, physical properties) and fundamental aspects of chemical engineering (material and energy balances, process design) are interlocked, and each aspect is presented by an instructor in that field.
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