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31.
Lothar Thiele 《Monatshefte für Chemie / Chemical Monthly》1992,123(10):865-874
Summary The kinetics of the reaction of phenylisocyanate with 1-butanol have been studied at low concentrations in carbon tetrachloride solution at three temperatures. The present paper describes the relation between the reaction rate and the concentration of the alcohol dimer and the 1:1 alcoholurethane associate. Therefrom we conclude that the monomeric alcohol does not play any significant part in the reaction. We explain the observed rate equation with the second-order term of the reactants with the equality of the productsk
AA
K
AA andk
AU
K
AU (rate constant and association constant of alcohol dimer and 1:1 alcohol-urethane associate).For the reaction of alcohol dimer H
=45.4 kJ mol–1 and S
=– 142J mol–1K–1. We interpret this result in terms of a six-cyclic transition state. 相似文献
32.
Molecular recognition and fluorescent sensing of Group 2A carcinogen-urethane was achieved in aqueous solution with endo-functionalized molecular tubes. The syn-configured molecular tube was found to be a good fluorescent sensor for urethane in water (concentration range:6.2-60 μmol/L) and in beer (concentration range:22.9-60 μmol/L). 相似文献
33.
Metal-free catalysts are preferred during these days in organic synthesis or in polymerizations.Sulfonic acid is reported to be efficient in catalyzing reactions between isocyanates and alcohols.In this work,synthesis of sulfonic acid immobilized organic nanoparticles (nanoacid) and its application in catalyzing urethane formation,are elaborated.The nanoacid can be simply prepared by miniemulsion polymerization with a reactive surfactant,namely sodium 4-((perfluoronon-8-en-1-yl) oxy) benzenesulfonate,followed by an acidification.From the images of scanning electron microscope,the nanoacid obtained is found to be narrowly dispersed and the average diameter is around 90 nm.The measured sulfur content is 0.5%,from which the content of sulfonic acid in the nanoparticles is calculated to be 0.16 mmol/g.When catalyzing urethane formation based on hexamethylene diisocyanate and n-butanol,the nanoacid catalyst exhibits considerable efficiency. 相似文献
34.
Urethane acrylate anionomer (APUA) as a kind of new type polymerizable emulsifier was synthesized using 2,4-toluene diisocyanate (TDI), polypropylene glycol (PPG), 2-hydroxyethyl methacrylate (HEMA) and dimethylolpropionic acid (DMPA). The critical micelle concentration (CMC) of APUA was measured by the methods of conductance and surface tension. The comparative studies between polymerizable emulsifier AUPA and conventional emulsifier sodium dodecyl sulfate (SDS) were carried out in the emulsion polymerization of methyl methacrylate (MMA). Polymerization kinetics,stability, size and morphology of the latex particles were investigated. It was found that in APUA both water soluble initiator potassium persulfate (KPS) and oil soluble initiator 2,2'-azobisisobutyronitrile (AIBN) can start the reaction of MMA, and the polymerization rate and yield were very high. On using AIBN as an initiator, the conversion-time behavior of MMA with APUA as emulsifier was different to that of SDS as emulsifier, signifying a different nucleation mechanism of the polymer latex particle. The average size of the two kinds of particles is about 50 nm. The particle size decreases with increasing emulsifier concentration. On using KPS as the initiator, APUA as emulsifier, cross-linking hydrogel of PMMA would be formed, but SDS was used as emulsifier and the hydrogel of PMMA was not present. 相似文献
35.
Monodisperse micron-sized polystyrene particles crosslinked using urethane acrylate were produced by dispersion polymerization
in ethanol solution and the effect of the crosslinked network structure on the polymerization procedure was studied. The influences
of the concentrations of the initiator and urethane acrylate on the particle diameter (D
n), the particle number density (N
p), and the polymerization rate (R
p) were found to obey the approximate relationships D
n ∝ [initiator]0.43 [urethane acrylate]0.05, N
p ∝ [initiator]−1.30 [urethane acrylate]0.19, and R
p ∝ [initiator]0.24 ± 0.02. The power-law dependence of D
n and N
p on the initiator concentration showed a similar trend to that of linear polystyrene reported in the literature. Especially,
it was found that urethane acrylate does not have a serious effect on D
n and N
p of the particles produced. The dependence of R
p on the initiator concentration was observed to be higher than that of linear polystyrene, suggesting that there is still
competition between heterogeneous polymerization and solution polymerization because of the crosslinked network structure
of the primary particle.
Received: 1 April 1999 Accepted in revised form: 29 June 1999 相似文献
36.
Mark H. Russell William R. Berti Bogdan Szostek Ning Wang Robert C. Buck 《Polymer Degradation and Stability》2010,95(1):79-7104
This study is the first to evaluate the rate of formation of perfluorooctanoate (PFO) from the aerobic biodegradation of a fluorotelomer-based urethane polymer and to use this information to assess the global environmental significance of this source. A fluorotelomer-based urethane polymer product test substance was studied in four aerobic soils over two years to determine the rate at which the fluorotelomer side-chains covalently bonded to the polymer backbone were cleaved and subsequently transformed to form the anions of perfluorocarboxylic acids including PFO. Over the two year duration of the experimental study, a polymer biodegradation half-life of 102 years (range: 28-241) was calculated for the urethane polymer based on regression analysis of the rate of PFO formation in four test soils. When this half-life was applied to the estimated total historic production, use and disposal of fluorotelomer-based urethane polymer, the annual potential global generation of PFO was estimated to be less than one tonne per year. 相似文献
37.
Isabelle Dez Lydie Pemberton Roger Dejaeger 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Synthesis of new urethane-phosphazene polymers: reaction of cyclotriphosphazenes containing hydroxyl functions with diisocyanates. 相似文献
38.
Yong Jin Kim 《Tetrahedron letters》2004,45(39):7205-7208
A microwave-assisted facile method for the preparation of various ureas, cyclic ureas, and urethanes has been developed that affords nearly quantitative yield of products at 120 °C (150 W), 71 kPa within 10 min using ZnO as a catalyst. The enhanced selectivity in this reaction is attributed to the deployment of ZnO whose absence results in poor yield and the generation of byproducts. 相似文献
39.
Lothar Thiele 《Monatshefte für Chemie / Chemical Monthly》1992,123(10):875-882
Summary The reaction between aromatic isocyanate and alcohol in nonpolar solvents at different alcohol and isocyanate concentrations and the effect of the presence of urethane in this solution at the start of the reaction have been examined. The results indicate that the rate constants of the observed second-order equation are dependent on the concentration of the reactants and of the urethane. 相似文献
40.
Dr. Youwei Ma Prof. Dr. Xuesong Jiang Prof. Dr. Zixing Shi Dr. José Augusto Berrocal Prof. Dr. Christoph Weder 《Angewandte Chemie (International ed. in English)》2023,62(36):e202306188
Devising energy-efficient strategies for the depolymerization of plastics and the recovery of their structural components in high yield and purity is key to a circular plastics economy. Here, we report a case study in which we demonstrate that vinylogous urethane ( VU ) vitrimers synthesized from bis-polyethylene glycol acetoacetates ( aPEG ) and tris(2-aminoethyl)amine can be degraded by water at moderate temperature with almost quantitative recovery (≈98 %) of aPEG . The rate of depolymerization can be controlled by the temperature, amount of water, molecular weight of aPEG , and composition of the starting material. These last two parameters also allow one to tailor the mechanical properties of the final materials, and this was used to access soft, tough, and brittle vitrimers, respectively. The straightforward preparation and depolymerization of the aPEG -based VU vitrimers are interesting elements for the design of polymer materials with enhanced closed-loop recycling characteristics. 相似文献