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101.
NMR parameters for bis(trimethyltin) oxide, sulphide, selenide and telluride have been measured by 1H{13C}, 1H{77Se}, 1H{119Sn}, 1H{125Te}, and 1H{117Sn} double resonance. Theories of 119Sn magnetic shielding and one-bond coupling constants are summarised and discussed in terms of the measured parameters. It is concluded that theoretical approximate expressions often used to estimate these parameters are inadequate when the tin atom is bound to selenium or tellurium. 相似文献
102.
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
103.
The aim of this research was to develop a quantitative treatment of the consequences of relatively slow initiation on M n and N (the number of molecules formed, Wp/M n , where Wp =weight of polymer formed) in living carbocationic polymerizations, particularly for the case of the incremental monomer addition (IMA) technique. This has been achieved by analysis of the effect of initiator efficiency (Ieff (%) = 100N/[I 0], where [I 0] = initiator input) on M n versus Wp , and N versus Wp plots. Three types of systems have been discerned: 1) Ieff equal to 100%; 2) Ieff constant but less than 100%; and 3) Ieff less than 100% but increasing with increasing number of monomer increments j by the IMA technique. Thus conditions can be found under which slowly initiating systems yield close to “ideal” product, i.e., one with M n = [M0 ]/[I0 ] and narrow molecular weight distribution (M w /M n ≈ 1.1). The corresponding equations and plots can be used to diagnose the mechanism. Subsequently, this quantitative analysis was used to describe a novel living system, trans‐2,5‐diacetoxy‐2,5‐dimethyl‐3‐hexene (DiOAcDMH6)/BCI3/isobutylene/CH3CI. This system produces linear t‐chlorine‐telechelic polyisobutylenes under homogeneous conditions. Surprisingly, cationation seems to be rate determining. This conclusion is illustrated by chemical equations. 相似文献
104.
J. P. Kennedy 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):885-895
Abstract The polymerization of styrene with the cationic initiator system AlR2Cl/RCl was investigated further. Earlier conclusions [1] were corroborated and expanded by an analysis of the number and weight average molecular weights. Alkyl halides with low (high) R?Cl bond dissociation energies are efficient (poor) coinitiators of the polymerization of styrene. In the presence of efficient RCl coinitiators, the molecular weights strongly decrease and the molecular weight distributions strongly increase with increasing conversions (Fig. 1). With poor cointiators, only low conversions are obtained even in the presence of large amounts of AlEt2Cl. The data are discussed in terms of a previously proposed mechanism [1]. 相似文献
105.
Ewa Dabek-Zlotorzynska Maria Piechowski Fang Liu Scott Kennedy Joseph F. Dlouhy 《Journal of chromatography. A》1997,770(1-2):349-359
Capillary electrophoresis (CE) with indirect UV detection utilizing a pyromellitate-based electrolyte was used for the routine analysis of major anions in atmospheric aerosols collected on filters with high-volume (Hi-Vol) samplers. The long-term reliability of the CE system was checked over an 8-month period during which over 2900 samples were analyzed. In addition, approximately 1100 samples were analyzed in parallel by ion chromatography (IC). It has been shown that acceptable analytical performance can be routinely obtained. The agreement between the CE and IC results is good, generally better than 20% at concentrations larger than 1 mg l−1. 相似文献
106.
Zhengjie Pi Joseph P. Kennedy James W. Summers 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3644-3651
The tertiary chlorine (Clt) content of vinyl chloride/2‐chloropropene copolymers [P(VC‐co‐2CP)] was determined by NMR spectroscopy. Copolymers containing 6.8–47.0 Clt's per P(VC‐co‐2CP) chain were used to initiate the cationic grafting of α‐methylstyrene, norbornadiene, indene, and norbornene with Et2AlCl under various conditions. Grafting was demonstrated by selective solvent extraction, and the effect of the experimental conditions on the grafting efficiency was examined. Select rheological and thermal characteristics of P(VC‐co‐2CP) grafts, including the glass‐transition temperature, heat deflection temperature, and discoloration upon heating, were studied. P(VC‐co‐2CP) carrying 7–11 poly(α‐methylstyrene) or polynorbornadiene branches per chain raised the glass‐transition temperature to, or above, that of a blend control. P(VC‐co‐2CP)s fitted with polyindene or polynorbornene branches were less effective in raising the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3644–3651, 2002 相似文献
107.
The nickel and zinc complexes of 2-aminomethylaniline (AMA) are reported. Both metals form the octahedral complex [M(AMA)2(ONO2)2] (M = Ni, Zn) where the aromatic ligands lie in the meridial plane with the anilino donors trans to one another. The remaining nitrates coordinate axially. A simple comparison with the nitrogen donor disposition (cis/trans) in nickel complexes of tetradentate N4 donor ligands derived from symmetric Schiff base ligands is presented. The discussion is extended to interrogate the bonding motifs of the nitrate ligands viz –ONO2 in the nickel complexes of AMA compared to the two motifs (viz O2NO and ONO2) that are isolated for the nickel complexes of the macrocycle hexamethyltetraazacyclotetradecane. 相似文献
108.
Regulatory problems caused by contamination, a frequently overlooked cause of veterinary drug residues 总被引:5,自引:0,他引:5
The occurrence of violative residues of veterinary medicines and other, unauthorised, drugs in food of animal origin is an issue of popular concern within the European Union. Violations can occur as a result of improper use of a licensed product or through the illegal use of an unlicensed substance. However, a "violative" analytical result does not necessarily mean that abuse has occurred. Contamination of animal feedingstuffs, environmental contamination and animal-to-animal transfer of drugs can also cause residue violations. This paper reviews these inadvertent causes of residues violations in food, and includes data generated using chromatographic and non-chromatographic methods of analysis. 相似文献
109.
The enantiospecific and regioselective rhodium-catalyzed allylic alkylation of a series of chiral nonracemic allylic carbonates, followed by ozonolysis and reductive lactonization, provides a convenient route to optically active gamma-lactones. Sequential alkylation and reductive alkylation furnished the alpha-quaternary-beta-ternary substituted gamma-lactone derivative as a >/=10:1 mixture of diastereoisomers. 相似文献
110.
David J. Kennedy Paul Todd Sam Logan Matthew Becker Klearchos K. Papas Lee R. Moore 《Journal of magnetism and magnetic materials》2007
Quadrupole magnetic flow sorting (QMS) is being adapted from the separation of suspensions of single cells (<15 μm) to the isolation of pancreatic islets (150–350 μm) for transplant. To achieve this goal, the critical QMS components have been modeled and engineered to optimize the separation process. A flow channel has been designed, manufactured, and tested. The quadrupole magnet assembly has been designed and verified by finite element analysis. Pumps have been selected and verified by test. Test data generated from the pumps and flow channel demonstrate that the fabricated channel and peristaltic pumps fulfill the requirements of successful QMS separation. 相似文献