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41.
Bla Ivn Joseph P. Kennedy Tibor Kelen Ferenc Tüdos 《Journal of polymer science. Part A, Polymer chemistry》1981,19(3):679-685
Colorless poly(vinyl chloride)s (PVC) containing up to 1.6 allylic chlorines per molecule have been prepared by controlled random dehydrochlorination with a strong base. The effect of temperature in the ?50 to +24°C range on the number of allylic chlorines and color of PVC has been investigated by ozonization experiments and UV–visible spectroscopy. A two-parameter kinetic model has been developed which quantitatively accounts for the observations and points the way for further research. 相似文献
42.
Yasuo Tsunogae J. P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1994,32(3):403-412
Preparatory to triblock synthesis experiments, the cationic polymerization of α-methylstyrene (αMeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCl4 initiating system in the presence of triethylamine (Et3N) as electron donor (ED) and CH3Cl/n-hexane mixed solvent in the ?80 to ?40°C range. Conversions are influenced by temperature, [TiCl4], [Et3N], and [αMeSt]. The polymerization of αMeSt is living at ?80°C: Both termination and chain transfer to monomer are frozen out, however, initiation is slow relative to propagation. Highly syndiotactic (>94%) Pα Mest was obtained. At?60deg;C initiator efficiency is ca. 100%, but termination becomes evident. Et3N may act both as Ed and as proton scavenger. Novel poly(α-methystyrene-b-isobutylene-b-α-methylstyrene) (PαMeSt-PIB-PαMeSt) triblocks have been synthesized by adding αMeSt to biliving polyisobutylene carbocations (⊕PIB⊕) in the ?80 to ?40°C range. The effects of temperature, solvent polarity, and [Et3N] on the block copolymerization have been investigated. At ?80°C, the rate of crossover from ⊕PIB⊕ to αMeSt is lower than that of propagation of PαMeSt⊕, so that the triblock is contaminated by PIB and PIB-b-PαMeSt. At ?60°C, crossover occurs preferentially. The rate of propagation relative to that of crossover is also reduced by lowering the solvent polarity and increasing the [Et3N]. High crossover efficiency and blocking efficiency can be obtained under optimum blocking conditions. The triblocks are novel thermoplastic elastomers (TPEs). © 1994 John Wiley & Sons, Inc. 相似文献
43.
Baseski HM Watson CJ Cellar NA Shackman JG Kennedy RT 《Journal of mass spectrometry : JMS》2005,40(2):146-153
In vivo microdialysis sampling was coupled to capillary liquid chromatography (LC)/electrospray ionization quadrupole ion trap mass spectrometry (MS) to monitor [Met]enkephalin and [Leu]enkephalin in the striatum of anesthetized and freely-moving rats. The LC system utilized a high-pressure pump to load 2.5 microl samples and desalt the 25 microm i.d. by 2 cm long column in 12 min. Samples were eluted with a separate pump at approximately 100 nl min(-1). A rapid gradient effectively separated the endogenous neuropeptides in 4 min. A comparison was made for operating the mass spectrometer in the MS2 and MS3 modes for detection of the peptides. In standard solutions, the detection limits were similar at 1-2 pM (2-4 amol injected); however, the reproducibility was improved with MS3 as the relative standard deviation was <5% compared with 20% for MS2 for 60 pM samples. For dialysate solutions, reconstructed ion chromatograms and tandem mass spectra had much higher signal-to-noise ratios in the MS3 mode, resulting in more confident detection at in vivo concentrations. The method was successfully used to monitor the peptides under basal conditions and with stimulation of peptide secretion by infusion of elevated K+ concentration. 相似文献
44.
Joseph P. Kennedy Tung-Ping Liao Suhas Guhaniyogi Victor S. C. Chang 《Journal of polymer science. Part A, Polymer chemistry》1982,20(11):3219-3227
β-Pinene was polymerized with H2O/BCl3 (protic) and p-dicumyl chloride and sym-tricumyl chloride (nonprotic) inifer systems in CH2Cl2 or CH2Cl2/n-C6H14 solvents from ?10 to ?70°C. The effect of solvent polarity, temperature, and monomer and inifer concentration on conversions and molecular weights was investigated. Low conversions and molecular weights, M?n = 1300–2500, obtained under these conditions suggest rapid termination. 相似文献
45.
Microscale sample deposition onto hydrophobic target plates for trace level detection of neuropeptides in brain tissue by MALDI-MS 总被引:1,自引:0,他引:1
Wei H Dean SL Parkin MC Nolkrantz K O'Callaghan JP Kennedy RT 《Journal of mass spectrometry : JMS》2005,40(10):1338-1346
A sample preparation method that combines a modified target plate with a nanoscale reversed-phase column (nanocolumn) was developed for detection of neuropeptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). A gold-coated MALDI plate was modified with an octadecanethiol (ODT) self-assembled monolayer to create a hydrophobic surface that could concentrate peptide samples into a approximately 200-500-microm diameter spot. The spot sizes generated were comparable to those obtained for a substrate patterned with 200-microm hydrophilic spots on a hydrophobic substrate. The sample spots on the ODT-coated plate were 100-fold smaller than those formed on an unmodified gold plate with a 1-microl sample and generated 10 to 50 times higher mass sensitivity for peptide standards by MALDI-TOF MS. When the sample was deposited on an ODT-modified plate from a nanocolumn, the detection limit for peptides was as low as 20 pM for 5-microl samples corresponding to 80 amol deposited. This technique was used to analyze extracts of microwave-fixed tissue from rat brain striatum. Ninety-eight putative peptides were detected including several that had masses matching neuropeptides expected in this brain region such as substance P, rimorphin, and neurotensin. Twenty-three peptides had masses that matched peaks detected by capillary liquid chromatography with electrospray ionization MS. 相似文献
46.
S. P. Nielsen A. Aarkrog P. A. Colgan E. McGee H. J. Synnott K. J. Johansson A. D. Horrill V. H. Kennedy N. Barbayiannis 《Journal of Radioanalytical and Nuclear Chemistry》1993,171(2):303-317
An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of137Cs, deposition of137Cs in three soil layers, biomass densities, concentrations of137Cs in pasture, and activity ratios (134Cs/137Cs) in soil and vegetation. The determination of total deposition of137Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other. 相似文献
47.
Irada S. Isayeva Alan N. Gent Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2002,40(12):2075-2084
A series of amphiphilic hydrogel tubules have been prepared by copolymerizing/crosslinking hydrophilic poly(dimethylacrylamide) segments with hydrophobic di‐, tri‐, and octamethacrylate‐telechelic polyisobutylene crosslinkers, and their elastic modulus and burst strength in the water‐swollen state were investigated. Because the burst characteristics of hydrogels have not yet been quantitatively investigated, equipment was designed and built to generate fundamental insight into the burst properties of thin‐walled (200–250 μm) narrow lumen (2–3 mm i.d.) water‐swollen tubules. The theory developed to describe quantitatively the inflation behavior of thin‐walled rubber tubules was adapted to treat our experimental observations. Changes in the burst strength, elastic modulus, and expansion during the inflation of hydrogel tubules were interpreted in terms of the molecular weight of the hydrophilic segments between crosslinking sites (Mc,hydrophilic), which in turn was calculated according to the rubber elasticity theory. According to these investigations, the burst strength of our water‐swollen amphiphilic tubules is in the 0.2–0.5 MPa range, which is sufficient for implantation and immunoisolatory applications. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2075–2084, 2002 相似文献
48.
Johnston AM Scrimgeour CM Kennedy H Handley LL 《Rapid communications in mass spectrometry : RCM》2003,17(11):1099-1106
The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil. 相似文献
49.
The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF2O + F2→ CF3OF. The list of catalysts for this process has now been enlarged to include NaF, MgF2, CaF2, SrF2, BaF2 and LaF3. Lithium fluoride and thorium fluoride also give CF3OF but are less active. Perhaps the substances CsF·HF, KAgF4 and NiF2 should be included in this list. Silver fluoride, usually as a mixture of AgF2 with AgF, has been known to catalyze the reaction of CF2O with F2 to give both CF3OF and CF3OOCF3. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF3OOCF3 is very high. It has now been shown that TIF3 behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF3OOCF3 than of CF3OF but require higher temperatures than AgF2 (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed. 相似文献
50.
He X Allan JF Noll BC Kennedy AR Henderson KW 《Journal of the American Chemical Society》2005,127(19):6920-6921
The reactions of magnesium and calcium bis(hexamethyldisilazide) with propiophenone have been studied with a view to determine the utility of these bases in the stereoselective enolization of ketones and to uncover the nature of the metal enolate intermediates produced. Both base systems are highly Z-selective when the reactions are conducted in the presence of polar solvents. However, in situ monitoring of the magnesium system in arene solution revealed a preference for E-enolate formation, which was confirmed by silyl enol ether trapping studies. Solution NMR studies of the magnesium system in toluene-d8 show the presence of a monomer-dimer equilibrium for the intermediate amidomagnesium enolates. This assignment is supported by the characterization of a disolvated amidomagnesium enolate dimer by crystallographic analysis. Comparative studies of the calcium system show distinctly different behavior. This is exemplified by the characterization of a novel solvent-separated ion pair complex and a monomeric amidocalcium enolate in the solid state. Solution NMR studies of the calcium system in pyridine-d5 reveal the co-existence of the heteroleptic amidocalcium enolate, the bisamide, the bisenolate and the ion pair complex. 相似文献