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891.
Siripon Anantawaraskul João B.P. Soares Paula M. Wood-Adams 《Macromolecular Symposia》2004,206(1):57-68
Crystallization analysis fractionation (Crystaf) is a new technique used to estimate the chemical composition distribution (CCD) of semi-crystalline copolymers. In this study, the effect of chain microstructure and operation parameters on Crystaf profiles was investigated using a series of ethylene/1-hexene copolymers and their blends. The Crystaf profiles were also modeled via stochastic simulation based on the distribution of average ethylene sequence lengths. 相似文献
892.
Olefinic thermoplastic elastomers can be prepared by incorporating semi‐crystalline macromonomers (e.g. isotactic or syndiotactic poly(propylene), high‐density polyethylene) onto amorphous backbones (e.g. atactic poly(propylene), ethylene/α‐olefin copolymers). The macromonomer incorporation reaction can be carried out in semi‐batch reactors by adding previously synthesized macromonomers to the reactor (ex situ approach), or by generating and incorporating the macromonomers in a single step (in situ approach). The differences in the microstructure of copolymers synthesized by in situ and ex situ techniques are explored herein through a mathematical model that can predict the concentration of linear and branched chains, their average molecular weights, polydispersity indices, and molecular weight distributions. In both cases linear chains predominate, but the ex situ approach produces a larger amount of branched chains with thermoplastic elastomer properties. Furthermore, for the in situ strategy, a significant amount of branched chains is only formed after the macromonomer concentration reaches a critical value.
893.
Siripon Anantawaraskul Joo B. P. Soares Paula M. Wood‐Adams 《Macromolecular theory and simulations》2003,12(4):229-236
The number and weight chemical composition distributions in random terpolymers were derived using a statistical approach. The solution was then generalized to comprise higher multicomponent copolymers. The analytical solution was verified with Monte Carlo simulations and by considering limiting cases. Chemical composition distributions for fractions of random terpolymers of various kinetic chain lengths were also investigated. In a similar way to the results for binary copolymers described by Stockmayer's distribution, broadening of the distribution is observed for low‐molecular‐weight chains.
894.
Fernanda S. Soares Raissa T. E. Ramalho Amanda C. Silva Mario C. U. Araujo 《Electroanalysis》2023,35(7):e202200486
A sensitive, simple, fast, and inexpensive method for determining diuron in water using square wave voltammetry and a glassy carbon electrode is presented. This method was developed to evaluate diuron contamination in river waters close to sugarcane cultivation, located in the metropolitan region of João Pessoa, in the state of Paraíba, Brazil. An analytical curve with a linear response ranging from 38.5–115.0 nmol L−1 (r2 = 0.993), a LOD equal 0.2 nmol L−1, and recovery rates from 88.0 to 108.0 %. The proposed method does not require any previous chemical treatment of the sample, thus contributing to green analytical chemistry. 相似文献
895.
Sanhueza Luis Garrido Karla Celis Freddy García Macarena Cáceres Cesar Moczko Ewa Díaz Ramiro J. Aguirre María García Camilo 《Journal of Solid State Electrochemistry》2023,27(6):1511-1521
Journal of Solid State Electrochemistry - Screen-printed electrodes (SPEs) have the advantage of being considered electrochemical cells that can be implemented in portable sensor applications. With... 相似文献
896.
897.
We show an approximation theorem of Runge type for solutions of the generalized Vekua equation , where L belongs to a class of degenerate elliptic planar vector fields and . To prove the theorem, we make use of an integral representation for the solutions of the generalized Vekua equation valid on relatively compact sets. As an application, we study the global solvability of the equation with and some of its consequences. 相似文献
898.
Emilay B. T. Diogo Dr. Fábio G. Delolo Gabriela A. P. Graça Esther R. S. Paz Ícaro A. O. Bozzi Prof. Dr. Renata Diniz Juliano P. Passos Prof. Dr. Tulio Matencio Dr. Liane K. Soares Prof. Dr. Diego Alves Pedro M. S. Costa Prof. Dr. Claudia Pessoa Prof. Dr. Cynthia L. M. Pereira Prof. Dr. Lutz Ackermann Prof. Dr. Eufrânio N. da Silva Júnior 《European journal of organic chemistry》2023,26(38):e202300506
Undivided electrochemical cells enable economical preparation of sulphur-containing naphthoquinones through electrochemical sulphenylation of quinoidal compounds. The environmentally friendly and efficient protocol eliminates the use of chemical oxidants and facilitates the synthesis of the desired molecules. This approach offers an efficient and versatile method to synthesize quinones that exhibit cytotoxicity against cancer cell lines. 相似文献
899.
Marcia G. Oliveira Bluma G. Soares Cludia M. F. Santos Milton F. Diniz Rita C. L. Dutra 《Macromolecular rapid communications》1999,20(10):526-531
Ethylene-propylene-diene rubber (EPDM) was reacted with thioacetic acid in the presence of 2,2′-azoisobutyronitrile (AIBN), giving rise to thioacetate-modified EPDM (EPDMTA). The extent of the incorporation was studied as a function of both thioacetic acid and AIBN concentration and reaction time. The products were analyzed by FTIR spectroscopy, sulfur content, and 1H NMR spectroscopy. The hydrolysis of EPDMTA in a NaOH methanolic solution resulted in mercapto-modified EPDM (EPDMSH). The addition of 5 wt.-% of this functionalized copolymer to a sulfur-vulcanized nitrile rubber (NBR)/EPDM (70 : 30 wt.-%) blend accelerated the vulcanization process as indicated by oscillating disk rheometer analysis. In addition, an improvement of mechanical and ageing properties was also observed. 相似文献
900.
Xianglin Zhu Huibin Zong Camilo J. Viasus Pérez Honghai Miao Wei Sun Zhimin Yuan Shenghua Wang Guixin Zeng Hui Xu Zaiyong Jiang Geoffrey A. Ozin 《Angewandte Chemie (International ed. in English)》2023,62(22):e202218694
To overcome the thermodynamic and kinetic impediments of the Sabatier CO2 methanation reaction, the process must be operated under very high temperature and pressure conditions, to obtain an industrially viable conversion, rate, and selectivity. Herein, we report that these technologically relevant performance metrics have been achieved under much milder conditions using solar rather than thermal energy, where the methanation reaction is enabled by a novel nickel-boron nitride catalyst. In this regard, an in situ generated HOB⋅⋅⋅B surface frustrated Lewis's pair is considered responsible for the high Sabatier conversion 87.68 %, reaction rate 2.03 mol gNi−1h−1, and near 100 % selectivity, realized under ambient pressure conditions. This discovery bodes well for an opto-chemical engineering strategy aimed at the development and implementation of a sustainable ‘Solar Sabatier’ methanation process. 相似文献