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排序方式: 共有95条查询结果,搜索用时 46 毫秒
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Neda Felorzabihi Jeffrey C. Haley Ghasem R. Bardajee Mitchell A. Winnik 《Journal of Polymer Science.Polymer Physics》2007,45(17):2333-2343
We measured the fluorescence decays of seven different amino‐coumarin dyes in polymer films of poly(methyl methacrylate) (PMMA), poly(styrene) (PS), and ethylene‐butene rubber (EBR); as well as in the small molecule analogs ethyl acetate and toluene. Many of the dye‐solvent and dye‐polymer combinations exhibited single exponential decays with lifetimes ranging from 2.3 to 3.9 ns. Small deviations from single exponential behavior occurred for most of the dyes in EBR. Significant deviations from single exponential behavior occurred for 7‐(diethylamino)‐2‐oxo‐2H‐1‐benzopyran‐3‐carboxylic acid (coumarin‐3) in ethyl acetate and in all polymer matrices and 2,3,6,7‐tetrahydro‐11‐oxo‐1H,5H,11H‐[1]benzopyrano[6,7,8‐ij]quinolizin‐10‐carboxylic acid (coumarin‐343) in all of the polymer matrices. Time‐resolved fluorescence spectra indicated the presence of two different excited states for coumarin‐3 and coumarin‐343 in PMMA; these spectra were qualitatively different from the time‐resolved spectra of coumarin‐3 in ethyl acetate. We rationalize these results in terms of the chemical functionalities of the various dyes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2333–2343, 2007 相似文献
64.
Roderic P. Quirk Deanna L. Gomochak Chrys Wesdemiotis Mark A. Arnould 《Journal of polymer science. Part A, Polymer chemistry》2003,41(7):947-957
The functionalization of polymeric organolithiums (PLi) with 3,4‐epoxy‐1‐butene (EPB) in a hydrocarbon solution yielded the corresponding hydroxybutene‐functionalized polymers in high yields (>95%). Three modes of addition of PLi to EPB were observed (1,4, 3,4, and 4,3). The products and chain‐end structures were characterized by 1H NMR, 13C NMR, attached‐proton‐test 13C NMR, calculated 13C NMR chemical shifts, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). The regioselectivity of the addition depended on the PLi chain‐end structure, the reaction conditions, and the addition of lithium salts or Lewis bases. In the absence of additives, the functionalization of poly(styryl)lithium (PSli) produced equal amounts of 1,4‐, 3,4‐, and 4,3‐addition, as determined by quantitative 13C NMR analysis. The use of a low temperature (6 °C), inverse addition, the addition of triethylamine (TEA; [TEA]/[PSLi] = 20) as a Lewis base, or dienyllithium chain ends produced polymers with only the 1,4‐addition product. Mild dehydration of the hydroxybutene‐functionalized polymer with p‐toluenesulfonic acid produced the corresponding diene‐functionalized macromonomer, as shown by MALDI‐TOF MS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 947–957, 2003 相似文献
65.
采用连续固定床反应器,考察了几种具有不同酸性和孔道尺寸的分子筛催化剂上丁烯-2齐聚反应的性能,并与固体磷酸(SPA)催化剂进行了对比.结果表明,分子筛催化剂的酸性和孔道尺寸是影响丁烯-2齐聚反应活性和选择性的重要因素.具有八元环孔道的分子筛的扩散阻力大,反应活性很低;十二元环分子筛的孔道降低了扩散阻力,有利于提高催化剂的低温活性和C9= 选择性;十元环分子筛的孔道尺寸和强酸中心可以提高催化剂的活性,促进C9= 生成.SPA催化剂上C9= 选择性低于30%,而具有强酸中心的十元环ZSM-5和ZSM-22分子筛,以及十二元环β分子筛催化剂上可高达50%以上,这说明分子筛催化剂具有更好的齐聚催化性能. 相似文献
66.
M. Fleisher V. Stonkus L. Leite E. Lukevics 《International journal of quantum chemistry》2002,88(5):670-675
Cyclodehydration of 1,4‐butanediol and 2‐butene‐1,4‐diol to the corresponding cyclic ethers was studied using the AM1 semiempirical method. It was established that the cyclodehydration reaction of 1,4‐butenediol and 2‐butene‐1,4‐diol is effected by converting of semicyclic conformers in the presence of acidic and basic active centers. The calculation results indicate that a concerted mechanism is probably realized in the cyclodehydration of both diols, while the sequences of the predicted steps in the cyclodehydration reaction for 1,4‐butanediol and 2‐butene‐1,4‐diol are different. The calculated reaction heats for 1,4‐butanediol and 2‐butene‐1,4‐diol transformations are ?184.029 and ?308.746 kcal/mol, respectively. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
67.
Quantum chemical modeling of but-1-ene isomerization to cis-but-2-ene and trans-but-2-ene in the presence of a gold atom has been carried out in the framework of the density functional theory with an extended
basis set, the PBE functional, and a pseudopotential with relativistic corrections included. Two possible mechanisms have
been considered, viz., with the formation of an intermediate σ-complex with one C(sp2)—Au bond and with gold insertion into the C—H bond. In the former case, the calculated energy barriers to two isomerization
stages are higher than 30 kcal mol−1. In the latter case, the reaction involves three stages and proceeds via a metal hydride complex with low barriers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1330–1337, July, 2008. 相似文献
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MoO3/ZrO2纳米固体强酸催化剂的制备及其在异丁烷-丁烯烷基化反应中的应用 总被引:1,自引:0,他引:1
利用AOT/异辛烷反胶束体系制备了MoO3/ZrO2纳米粒子.TEM结果表明,反胶束法制得粒子的粒径均匀,95%以上处于38~60nm之间.将此纳米粒子负载于γ-Al2O3上,呈现高度分散状态.NH3-TPD和烷基化反应的测定结果表明,其酸量和反应活性明显高于浸渍法和溶胶-凝胶法制备的样品,烷基化产物中C8的含量在79%左右. 相似文献
70.
在负载H3PO4的固体上3,3,4-三甲基-4-戊烯-2-酮的催化合成 总被引:1,自引:0,他引:1
3,3,4-Trimethyl-4-penten-2-one has been synthesized by the acylation of 2,3-dimethyl-2-butene with acetic anhydride in the presence of soild-supported H3PO4.By comparison of the acylation reactions of 2,3-dimethyl-2-butene with acetic anhydride over various soilds-supported H3PO4,it was found that K10 clay,silicagel,HY zeolite and HMordenite were good supports.The results obtined indicate that the soild-supported small amounts of H3PO4 possessed higher catalytic activities,For obatining a higher yield of 3,3,4-trimethyl-4-penten-2-one different supports required different modification methods. 相似文献