Novel low energy hydrogen–deuterium isotope breakthrough separation using a trapdoor zeolite

AbstractCs-chabazite, a type of zeolite with caesium counter-cations, possesses interesting gas separation properties due to a highly selective molecular “trapdoor” effect. Herein the use of this material for H2/D2 isotope separation is demonstrated. Isotope separation was achieved using breakthrough separation with a single pass through a packed bed at moderate temperatures (293K) and pressures (0.17MPa) when one species was in a sufficiently low concentration. The breakthrough separation curves were successfully modelled using the Thomas kinetic breakthrough model and the Yoon and Nelson kinetic breakthrough model, where working transferable kinetic rate constants were developed. Use of this material for hydrogen isotope separation would significantly lower the total energy demand compared with current hydrogen isotope separation techniques such as cryogenic distillation and is applicable to separating out low concentrations of D2 (0.0156%) present in standard grade H2

Synthesis of high molecular weight near-monodisperse poly(4-methylstyrene) by anionic polymerization

The synthesis of high molecular weight near-monodisperse poly(4-methylstyrene) is described. The polymerizations were conducted using sec-butyllithium as initiator and benzene as solvent. Chain transfer involving the p-methyl group is effectively prevented by the combination of low polymerization temperature (0°C) and limited (<60%) conversion. © 1989 Springer-Verlag

Solvent and Temperature Influences on Polystyrene Unperturbed Dimensions

The unperturbed chain dimensions of near-monodisperse atactic polystyrenes were evaluated from intrinsic viscosity measurements in 12 different solvents under θ or near-θ conditions over the temperature range 8.5-75.0 °C. In consonance with the indications of other workers, larger values of unperturbed dimensions were found in cyclic hydrocarbon solvents than in other ideal solvents at similar temperatures. Negative values for the temperature coefficient of chain dimensions were found within the three solvent series examined. Under conditions where specific solvent effects are eliminated or minimized, measurements yielded results in excellent agreement with the theoretical predictions for atactic polystyrene, i.e., d In (r2)0/dt = -1.1 X 10-3 deg-1. © 1985, American Chemical Society. All rights reserved

Acetylene-functionalized lithium initiators for anionic polymerization. Powerful precursors for "click" chemistry

Two novel anionic acetylene-functionalized initiators, 5-trimethylsilyl-4- pentynyllithium (TMSPLi) and 5-triethylsilyl-4-pentynyllithium (TESPLi), were synthesized and characterized by 1H NMR, 13C NMR, and GC-MS. TMSPLi was successfully used for the polymerization of styrene, but not for the polymerization of isoprene and butadiene. On the other hand, TESPLi exhibited all characteristics of an anionic initiator for the (co)polymerization of styrene, isoprene, and butadiene. TESPLi is ideal for the synthesis of living well-defined (co)polymers with acetylene end groups, perfect candidates for "click" reactions and at the same time possessing all the potential of living anionic polymerization for the synthesis of well-defined complex macromolecular architectures. © 2011 American Chemical Society

Association of End-Functionalized Block Copolymers. Light Scattering and Viscometric Studies

The dilute solution properties of diblock and triblock copolymers of styrene and isoprene with one dipolar sulfobetaine group at either or both ends of the chain were examined in carbon tetrachloride by static and dynamic light scattering as well as by viscometry. The copolymers were prepared by anionic polymerization techniques using [3-(dimethylamino)propyl] lithium as initiator. The tertiary amine groups were converted to sulfobetaines by reaction with cyclopropanesultone. Aggregation numbers derived from static and dynamic methods are in good agreement and decrease with increasing molecular weight of the polymeric tail. Aggregates seem to be polydisperse and stable for long periods of time. Although aggregation is reduced when small amounts of 2-methylcyclohexanol are added, in CCl4 solutions, it persists even at concentrations of alcohol as high as 5% (v/v). Gels, formed by the difunctional species, are also destroyed by addition of alcohol. There is evidence for intramolecular association in very dilute solutions of the difunctional species. The hydrodynamic behavior of the aggregates, formed by the monofunctional species, resembles that of star polymers in general. Comparisons with theoretical predictions show that the behavior of the aggregates is best described by the linear head-packing model. © 1994, American Chemical Society. All rights reserved

Solution properties and characteristic ratio of near-monodisperse poly(tert-butyl methacrylate)

The dilute solution properties of six near-monodisperse samples of poly(tert-butyl methacrylate) covering the molecular weight range {Mathematical expression} are reported. Unperturbed chain dimensions were derived from a combination of light scattering and intrinsic viscosity data. A characteristic ratio (C∞) of 12.0 was obtained in the theta solvent cyclohexane at 10°C. This C∞ value is considerably larger than the value of 8.8 reported previously for poly(n-butyl methacrylate) and reflects the greater bulkiness of the tert-butyl substituent and also, possibly, tacticity effects. © 1990 Springer-Verlag

Synthesis and unperturbed dimensions of poly(diphenylmethyl methacrylate)

The synthesis, fractionation, and characterization of poly(diphenylmethyl methacrylate) (PDPMM) are described. Analysis of tacticity by 13C nuclear magnetic resonance (NMR) revealed a high (25%) isotactic content. Results of low‐angle light scattering and intrinsic viscosity measurements in toluene indicate that PDPMM chains behave as random coils and that toluene is a thermodynamically good solvent. The characteristic ratio C∞ of the chains was determined from viscosity measurements in a near‐theta solvent, 3‐heptanone at 45°C. The corresponding value of C∞ = 14.0 is consistent with previous work on poly(triphenylmethyl methacrylate), C∞ = 20.3, and poly(benzyl methacrylate), C∞ = 10.0, and reflects the bulkiness of the side group and the increase in isotactic content of the chains with increasing substitution. Copyright © 1990 John Wiley & Sons, Inc

Model mono-, di-, and tri-ω-functionalized three-arm star polybutadienes. Association behavior in dilute solution by dynamic light scattering and viscometry

The dilute solution properties of three-arm star polybutadienes with one, two, and three dimethylamino or sulfobetaine end groups were studied in tetrahydrofuran (THF) and cyclohexane by dynamic light scattering and viscometry. The polymers were prepared by anionic polymerization techniques using [3-(dimethylamino)propyl]lithium or sec-BuLi as initiator and methyltrichlorosilane as linking agent. The dimethylamino groups were converted to highly polar sulfozwitterion groups by reaction with cyclopropanesultone. In the case of the amine-capped polybutadienes, the hydrodynamic behavior in cyclohexane and THF was almost the same, meaning the absence of any appreciable association in cyclohexane. For the zwitterionic polymers, the hydrodynamic, RH, and viscometric radii, Rv, in cyclohexane are larger than those for the corresponding amine-capped samples, showing the existence of aggregation. The difference decreases as the number of functional groups increases, which is in agreement with previous static methods results. The micelles formed by the monofunctional species behave hydrodynamically as star polymers with functionality equal to 2Nw, where Nw is the weight-average degree of association. The Rv/RH ratio is lower than unity (0.51-0.89), meaning that during the flow in the viscometer there is some disassociation of the aggregates

End-functionalized block copolymers of styrene and isoprene. A d.s.c. study

The influence of the end groups on the glass transition temperature, Tg, of the polyisoprene block of styrene-isoprene diblocks was studied by differential scanning calorimetry. The end-functionalized styrene-isoprene diblock samples used have dimethylamino and sulfobetaine groups attached on the polyisoprene chain end. An increase in the low temperature (polyisoprene-type) Tg value was observed for the lower molecular weight zwitterion capped polymers. This effect is attributed to restricted segmental mobility of the polyisoprene chains found in the proximity of the ionic aggregates. Copyright © 1996 Elsevier Science Ltd