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71.
The thermal degradation of thermosetting materials prepared by cationic copolymerization of mixtures of different proportions of diglycidylether of bisphenol A (DGEBA) with 6,6-dimethyl (4,8-dioxaspiro[2.5]octane-5,7-dione) (MCP) initiated by ytterbium or lanthanum triflate or using a conventional initiator, BF3·MEA was investigated. To study the thermal degradation, several techniques were used such as thermogravimetry (TGA), infrared spectroscopy (FTIR) and calorimetry (DSC) and the volatiles evolved during degradation were identified by mass spectrometry. The materials prepared possess the characteristics of thermally degradable thermosets, due to the presence of ester groups in the polymer chain, which are broken at the beginning of degradation. The degradability increased when lanthanide triflates were used in the curing, especially the ytterbium salt and when the proportion of MCP in the material increased. 相似文献
72.
Ramis X. Salla J. M. Cadenato A. Morancho J. M. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):707-718
The curing of a thermosetting powder coating was studied by means of differential scanning calorimetry (DSC). The isothermal
cure was simulated by non-isothermal experiments. The results of the simulation were compared with experimental isothermal
data. From non-isothermal isoconversional procedures (free model), it was concluded that these permit simulation of the isothermal
cure but do not enable us to determine the complete kinetic triplet (A preexponential factor, E activation energy, f(a) and/or g(a) function of conversion). Non-isothermal procedures based on a single heating rate or on master curves present difficulties
for determination of all the kinetic parameters, due to the compensation effect between preexponential factor and activation
energy. The kinetic triplet can be determined by a combination of various non-isothermal methods or by using experimental
isothermal data in addition to non-isothermal data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
73.
We report an analysis of the pH-dependent dissociation of a multimeric metalloprotein, xylose isomerase from Streptomyces rubiginosus (XI), by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Xylose isomerases are industrially significant enzymes that catalyze interconversion of aldose and ketose sugars. XI is biologically active as a approximately 173-kDa tetrameric complex, comprised of four identical approximately 43-kDa subunits and eight metal cations, unequivocally identified as the Mg(2+) cations in this work. ESI FT-ICR mass spectra of XI measured in the pH range of 3.0-6.9 indicated that the dissociation of the intact holo-tetramer is initiated by the loss of all eight Mg(2+) cations at pH 相似文献
74.
Silvestri Siara Stefanello Nádia da Silveira Salla Julia Foletto Edson Luiz 《Research on Chemical Intermediates》2019,45(9):4299-4313
Research on Chemical Intermediates - In this work, different synthesis methods of zinc stannate (Zn2SnO4–ZTO) were proposed in order to obtain a material with a... 相似文献
75.
Thermoset Cure Kinetics by Isoconversional Methods 总被引:1,自引:0,他引:1
J. M. Salla A. Cadenato X. Ramis J. M. Morancho 《Journal of Thermal Analysis and Calorimetry》1999,56(2):771-781
The curing kinetics of thermosets based on unsaturated polyester resin crosslinked with styrene was studied by differential
scanning calorimetry (DSC). The isoconversional kinetic analysis was applied to non-isothermal data. The results obtained
show a dependence of the activation energy (Eα) on conversion (α) that proves the existence of a multistep process and a complex kinetic scheme that must be interpreted
in terms of chemical and physical mechanisms. The interrelationship of the Arrhenius parameters obtained from the isoconversional
kinetic data has been used as a tool to investigate the production of free radicals by the action of a promoter (cobalt octoate)
and the temperature on the initiator (methyl ethyl ketone peroxide). An optimum promoter/initiator ratio has been found.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
76.
Giliandro Farias Cristian A. M. Salla Murat Aydemir Ludmilla Sturm Pierre Dechambenoit Fabien Durola Bernardo de Souza Harald Bock Andrew P. Monkman Ivan H. Bechtold 《Chemical science》2021,12(45):15116
Halogenation of a twisted three-fold symmetric hydrocarbon with F, Cl or Br leads to strong modulation of triplet–triplet annihilation and dual phosphorescence, one thermally activated and the other very persistent and visible by eye, with different relative contributions depending on the halide. The room temperature phosphorescence is highly unusual given the absence of lone-pair-contributing heteroatoms. The interplay between the spin–orbit coupling matrix elements and the spatial configuration of the triplet state induces efficient intersystem crossing and thus room temperature phosphorescence even without relying on heteroatomic electron lone pairs. A ninefold increase of the ISC rate after introduction of three bromine atoms is accompanied by a much higher 34-fold increase of phosphorescence rate.Twisted π-systems investigation showed a very unusual HAE, influencing independently the ISC and the dual phosphorescence emission, one being very persistent at room temperature and visible by eye in powder. 相似文献
77.
The Isothiocyanato Moiety: An Ideal Protecting Group for the Stereoselective Synthesis of Sialic Acid Glycosides and Subsequent Diversification 下载免费PDF全文
Appi Reddy Mandhapati Dr. Salla Rajender Jonathan Shaw Prof. Dr. David Crich 《Angewandte Chemie (International ed. in English)》2015,54(4):1275-1278
The preparation of a crystalline, peracetyl adamantanyl thiosialoside donor protected by an isothiocyanate group is described. On activation at ?78 °C in the presence of typical carbohydrate acceptors, this donor gives high yields of the corresponding sialosides with exquisite α‐selectivity. The high selectivity extends to the 4‐O‐benzyl‐protected 3‐OH acceptors, which are typically less reactive and selective than galactose 3,4‐diols. Treatment of the α‐sialosides with tris(trimethylsilyl)silane or allyltris(trimethylsilyl)silane results in replacement of the C5? N5 bond by a C? H or a C? C bond. The reaction of the isothiocyanate‐protected sialosides with thioacids generates amides, while reaction with an amine gives a thiourea, which can be converted into a guanidine. The very high α‐selectivities observed with the new donor and the rich chemistry of the isothiocyante function considerably extend the scope for optimization at the sialoside 5‐position. 相似文献
78.
Xavier Ramis Josep María Salla Jordi Puiggalí 《Journal of polymer science. Part A, Polymer chemistry》2005,43(6):1166-1176
A potassium salt of N‐chloroacetyl‐11‐aminoundecanoate was thermally polymerized to obtain the corresponding poly(glycolic acid‐alt‐11‐aminoundecanoic acid). A kinetic study was then performed that was based on isothermal and nonisothermal polymerizations performed in a differential scanning calorimeter. The complete kinetic triplet was determined (the activation energy, pre‐exponential factor, and integral function of the degree of conversion). A kinetic analysis was performed with an integral isoconversional procedure (free model), and the kinetic model was determined both with the Coats–Redfern method (the obtained isoconversional value being accepted as the effective activation energy) and through the compensation effect. The polymerization followed a three‐dimensional growth‐of‐nuclei (Avrami) kinetic mechanism. Isothermal polymerization was simulated with nonisothermal data. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1166–1176, 2005 相似文献
79.
Cristina Mas Xavier Ramis Josep Maria Salla Ana Mantecn Angels Serra 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1711-1721
Mixtures of the diglycidylether of bisphenol A (DGEBA) and phthalide (PT) or 3,3′‐diphthalide (DPT) were cured using ytterbium or lanthanum triflate as catalyst. The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and quantify the evolution of the epoxide and lactone groups. The Tg of the crosslinked materials increased when the proportion of lactone in the curing mixture decreased. The kinetics was studied with DSC experiments and isoconversional procedures. The differences in the reactivity of the systems were related to the Lewis acidity of the lanthanide salt used as initiator. The increase in the proportion of lactone leads to an increase in the reaction rate. The shrinkage was determined from the densities before and after curing and its evolution was studied by thermomechanical analysis. The materials obtained were characterized by thermogravimetry and dynamic mechanical thermal analysis. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1711–1721, 2006 相似文献
80.
Roser Cervellera Xavier Ramis Josep Maria Salla Angels Serra Ana Mantecn 《Journal of polymer science. Part A, Polymer chemistry》2006,44(15):4546-4558
Ytterbium and lanthanum triflates were used as initiators to cure a mixture of diglycidylether of bisphenol A (DGEBA) and 5,5‐dimethyl‐1,3‐dioxane‐2‐one (DMTMC). The evolution of the curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing process. We observed the formation of a five‐membered cyclic carbonate, which remains unreacted at the chain ends because of an equilibrium process between the spiroortho carbonates that had formed as intermediate species and also the loss of CO2, which was quantified by thermogravimetry. The kinetics were studied by DSC and analyzed by isoconversional procedures. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the thermosets obtained. The phenomenological changes that take place during curing were studied and represented in a time‐temperature‐transformation (TTT) diagram. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4546–4558, 2006 相似文献