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81.
Andrew J. D. Magenau Todd R. Hartlage Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2010,48(23):5505-5513
Thiol‐terminated polyisobutylene (α,ω‐PIB‐SH) was synthesized from thiourea and α,ω‐bromine‐terminated PIB in a three‐step, one‐pot procedure, using a cosolvent system of 1:1 (v:v) heptane:dimethylformamide. The initial alkylisothiouronium salt was produced at 90 °C. Aqueous base hydrolysis at 110 °C resulted in thiolate chain ends, which were re‐acidified to form telechelic PIB‐SH. 1H and 13C NMR confirmed thiol functionality and complete terminal halogen conversion. Thiol‐based “click” reactions were used to demonstrate PIB‐SH utility. Alkyne‐terminated PIB was synthesized by a phosphine‐catalyzed thiol‐ene Michael addition with propargyl acrylate. Reaction of this product with 6‐mercaptohexanol produced tetrahydroxy‐functional PIB by a sequential thiol‐ene/thiol‐yne procedure. 1H NMR confirmed the structures of both products. PIB‐SH was reacted with isocyanates in the presence of base to produce polythiourethanes. A model reaction used phenyl isocyanate in THF with catalytic triethylamine. Similar conditions were used to produce PIB‐based thiourethanes with and without a small‐molecule chain extender. Increased molecular weights and thiol group conversion were observed with GPC and 1H NMR, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
82.
Brian D. Mullen Chau N. Tang Robson F. Storey 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):1978-1991
The synthesis, characterization, and ring‐opening polymerization of a new cyclic carbonate monomer containing an allyl ester moiety, 5‐methyl‐5‐allyloxycarbonyl‐1,3‐dioxan‐2‐one (MAC), was performed for the first time. MAC was synthesized in five steps in good yield beginning from the starting material, 2,2‐bis(hydroxymethyl)propionic acid. Subsequent polymerization and copolymerizations of the new cyclic carbonate with rac‐lactide (rac‐LA) and ?‐caprolactone (CL) were attempted. Rac‐LA copolymerized well with MAC, but CL copolymerizations produced insoluble products. Oligomeric macroinitiators of MAC and rac‐LA were synthesized from stannous ethoxide, and both macroinitiators were used for the controlled ring‐opening polymerization of rac‐LA. The polymerization kinetics were examined by monitoring the disappearance of the characteristic C? O ring stretch of the monomer at 1240 cm?1 with real‐time in situ Fourier transform infrared spectroscopy. Postpolymerization oxidation reactions were conducted to epoxidize the unsaturated bonds of the MAC‐functionalized polymers. Epoxide‐containing polymers may allow further organic transformations with various nucleophiles, such as amines, alcohols, and carboxylic acids. NMR was used for microstructure identification of the polymers, and size exclusion chromatography and differential scanning calorimetry were used to characterize the new functionalized poly(ester‐carbonates). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1978–1991, 2003 相似文献
83.
In this paper, a new variable-metric method based on a rational, rather than a quadratic, model is proposed. A switching algorithm is also introduced which selects either the standard quadratic model or the new rational model, depending on which has the smallest condition number. Several functions are used to test the new method, and it is concluded that it is as efficient as the standard model in general and is superior for problems of high dimensionality. Considerable improvement is also obtained for high-dimensional problems when the switching algorithm is used. 相似文献
84.
The structural phase transition in RbCaF3 has been examined by observing super lattice points by means of neutron diffraction. There is one structural phase transition with the R25x soft mode phonon condensation up to 4.2 K. The rotation angle of CaF6 octahedra, Ø, is calculated as 8.64 degrees at 60 K. The temperature dependence of Ø is also given. 相似文献
85.
Stevie Brown Dr. Ewan Cruickshank Prof. John M. D. Storey Prof. Corrie T. Imrie Prof. Damian Pociecha Dr. Magdalena Majewska Dr. Anna Makal Prof. Ewa Gorecka 《Chemphyschem》2021,22(24):2506-2510
Liquid-crystal materials exhibiting up to three nematic phases are reported. Dielectric response measurements show that while the lower temperature nematic phase has ferroelectric order and the highest temperature nematic phase is apolar, the intermediate phase has local antiferroelectric order. The modification of the molecular structure by increasing the number of lateral fluorine substituents leads to one of the materials showing a direct isotropic-ferronematic phase transition. 相似文献
86.
Graham R. Rideal Jamie Storey Thomas R. Morris 《Particle & Particle Systems Characterization》2000,17(2):77-82
This paper describes the preparation, measurement and use of microspheres for calibrating individual test sieves. Using a 63 µm sieve as an example, 2.5 million apertures, or 80% of the surface is examined in under 2 minutes. Because of the narrowness of the size distribution, a 5% difference in percent passing only results in a mean aperture difference of 1 µm, indeed, the measurement uncertainty for all 24 tests performed was only 0.7 µm. The calibration is independent of the method of shaking and can be used for most sieves. 相似文献
87.
In this paper, low-order Newton methods are proposed that make use of previously obtained second-derivative information by suitable preconditioning. When applied to a particular 2-dimensional Newton method (the LS method), it is shown that a member of the Broyden family of quasi-Newton methods is obtained. Algorithms based on this preconditioned LS model are tested against some variations of the BFGS method and shown to be much superior in terms of number of iterations and function evaluations, but not so effective in terms of number of gradient evaluations. 相似文献
88.
89.
Classical molecular dynamics modelling has been used to obtain new models of 50CaO·50P2O5 and 50MgO·50SiO2 glasses and, together with previously published models of 63CaO·37Al2O3, and 50CaO·50SiO2 glasses, these have been inspected to evaluate structural features. For the first time, models of glasses near the eutectic in three systems, aluminate, silicate, and phosphate, with the same modifier, Ca, have been compared. All have short range order which is similar to that in crystals of the same composition, 5CaO·3Al2O3, CaSiO3 and Ca(PO3)2. There is a clear trend in bonding of bridging oxygen to Ca, which is dominant in aluminate glass, common in silicate glass, and absent in phosphate glass. Preliminary results for 50MgO·50SiO2 glass show unusual behaviour because ~ 5% of oxygen is present as “non-network” oxygen, i.e. bonded only to Mg. The models show broader Qn distributions than seen in NMR experiments, and this remains an area for improvement of MD modelling of glasses. The distributions of Ca in the models have been studied using the pair distribution function TCaCa(r) which is found to be similar in the three glasses, and also similar to the previous experimental measurement for 50CaO·50SiO2 glass. The distributions of Ca are markedly different in the glasses compared to the crystals, being isotropic in the former and anisotropic in the latter, which should be a factor in glass forming ability. 相似文献
90.
Daniel A Paterson Jordan P Abberley William TA Harrison John MD Storey 《Liquid crystals》2017,44(1):127-146
ABSTRACTThe synthesis and characterisation of several members of the 1,ω-bis(4-cyanobiphenyl-4′-yl) alkane (CBnCB) and the 1-(4-cyanobiphenyl-4′-yloxy)-ω-(4-cyanobiphenyl-4′-yl) alkane (CBnOCB) homologous series are reported. The new odd members described CB5CB, CB13CB, CB4OCB, CB8OCB and CB10OCB all exhibit twist-bend nematic and nematic phases. The members of these series already reported in literature, CB7CB, CB9CB, CB11CB and CB6OCB, were also prepared in order to allow for a direct comparison of their transitional properties. The properties of these dimers are also compared to those of the corresponding members of the 1,ω-bis(4-cyanobiphenyl-4,-yloxy) alkanes (CBOnOCB). For any given total spacer length, for odd members of these series, the nematic–isotropic transition temperatures and associated entropy changes are greatest for the CBOnOCB dimer and lowest for the CBnCB dimer. These trends are understood in terms of molecular shape. For short spacer lengths, the twist-bend nematic–nematic transition temperature (TNTBN) is higher for the CBnOCB series than for the CBnCB series but this is reversed as the spacer length increases. Of the CBOnOCB dimers, a virtual value of TNTBN was estimated for CBO3OCB and TNTBN was measured for CBO5OCB. These values are considerably lower than those observed for the corresponding members of the CBnCB or CBnOCB series. The dependence of TNTBN on molecular structure is discussed not only in terms of the molecular curvature but also in the ability of the molecules to pack efficiently. As the temperature range of the preceding nematic phase increases, so the twist-bend nematic–nematic transition entropy change decreases and the transition approaches second order for the longer spacers. For comparative purposes, the transitional behaviour of the even-membered dimers CB6CB, CB5OCB and CBO4OCB is reported and differences accounted for in terms of molecular shape. 相似文献