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Search Results: 1 - 10 of 35150 matches for " MARIO RODRíGUEZ-BAEZA "
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OBTENTION OF POWDERED CERAMIC MATERIAL BY PYROLYSIS OF POLY [(DIMETHYLSILOXANE)-CO-(DIMETHYLSILAZANE)] COPOLYMERS AS PRECURSORS
RODRíGUEZ-BAEZA,MARIO; TRUJICHETT BRITO,MARíA JOSé;
Journal of the Chilean Chemical Society , 2006, DOI: 10.4067/S0717-97072006000200015
Abstract: a series of new poly(siloxane) and poly(silazane) derivates were synthesized by cationic ring opening mass copolymerization of the cyclic monomers octamethylcyclotetrasiloxane and hexamethylcyclotrisilazane, obtaining poly[(dimethylsiloxane)-co-(dimethylsilazane) ] copolymers with different concentrations of the comonomer units. the molar masses of the soluble fractions of the copolymers and of the macrocycles generated in the copolymerization reaction medium, were determined by gel permeation chromatography. thermogravimetric analysis shows that poly(dimethylsiloxane) is more stable than the copolymers and the homopolymer poly(dimethylsilazane). differential scanning calorimetry of poly(dimethylsilazane) presents a melting endotherm, indicating that this homopolymer is crystalline. the copolymers were characterized by ft-ir and 1h and 13c nmr spectroscopy.. the polymers were thermally cured and pyrolysed, obtaining ceramic powder. the morphology of the ceramic powder, studied by scanning electronic microscopy, corresponds to highly uniform spherical particles. the ceramic material was characterized by ft-ir. it was shown that these cyclic monomers copolymerize and that they constitute pre-polymer precursors of the powdered ceramic material since the products have si, c, n and o atoms
OBTENTION OF POWDERED CERAMIC MATERIAL BY PYROLYSIS OF POLY [(DIMETHYLSILOXANE)-CO-(DIMETHYLSILAZANE)] COPOLYMERS AS PRECURSORS
MARIO RODRíGUEZ-BAEZA,MARíA JOSé TRUJICHETT BRITO
Journal of the Chilean Chemical Society , 2006,
Abstract: A series of new poly(siloxane) and poly(silazane) derivates were synthesized by cationic ring opening mass copolymerization of the cyclic monomers octamethylcyclotetrasiloxane and hexamethylcyclotrisilazane, obtaining poly[(dimethylsiloxane)-co-(dimethylsilazane) ] copolymers with different concentrations of the comonomer units. The molar masses of the soluble fractions of the copolymers and of the macrocycles generated in the copolymerization reaction medium, were determined by gel permeation chromatography. Thermogravimetric analysis shows that poly(dimethylsiloxane) is more stable than the copolymers and the homopolymer poly(dimethylsilazane). Differential scanning calorimetry of poly(dimethylsilazane) presents a melting endotherm, indicating that this homopolymer is crystalline. The copolymers were characterized by FT-IR and 1H and 13C NMR spectroscopy.. The polymers were thermally cured and pyrolysed, obtaining ceramic powder. The morphology of the ceramic powder, studied by scanning electronic microscopy, corresponds to highly uniform spherical particles. The ceramic material was characterized by FT-IR. It was shown that these cyclic monomers copolymerize and that they constitute pre-polymer precursors of the powdered ceramic material since the products have Si, C, N and O atoms
THERMOGRAVIMETRIC STUDY OF THE FORMATION OF CROSS-LINKED STRUCTURES IN THE SYNTHESIS OF POLY(METHYLSILOXANE)
Rodríguez-Baeza,Mario; Neira C.,Andrónico; Aguilera J.,Carlos;
Journal of the Chilean Chemical Society , 2003, DOI: 10.4067/S0717-97072003000200013
Abstract: the thermogravimetric analysis resulted to be an analytical technique, very illustrative that allowed us to determine the thermal stability, molecular structure and the formation process of cross-linked structures, in the synthesis of poly(methylsiloxane). poly(methylsiloxane) was synthesized by cationic ring-opening polymerization of the cyclic monomer 1, 3, 5, 7-tetramethylcyclotetrasiloxane. a series of polymers were obtained by varying polymerization times. the initial and maximum decomposition temperatures increase to higher polymerization time until constant values are reached. at short polymerization time mainly linear polymers are formed with small fraction of cross-linked structures. at higher polymerization time partial and total cross-linked polymers are obtained. formation of cross-linked structures stabilizes thermically the whole polymeric matrix, being the stability proportional to the cross-linking degree. the thermogravimetric analysis allowed us to formulate a method to determine the cross-linking degree of these polymers. ft-ir analysis showed the existence of the absorption band of variable intensity, corresponding to the vibration of the si-h bond, in all the studied polymers. ft-ir spectra of the residual ceramic powder obtained by pyrolysis showed the typical absorption bands of these materials. the characterization of the polymers was also carried out by thermomechanical analysis. kinetic decomposition parameters such us pre-exponential factors, decomposition reaction orders and activation energies were determined by thermogravimetry.
THERMOGRAVIMETRIC STUDY OF THE FORMATION OF CROSS-LINKED STRUCTURES IN THE SYNTHESIS OF POLY(METHYLSILOXANE)
Mario Rodríguez-Baeza,Andrónico Neira C.,Carlos Aguilera J.
Journal of the Chilean Chemical Society , 2003,
Abstract: The thermogravimetric analysis resulted to be an analytical technique, very illustrative that allowed us to determine the thermal stability, molecular structure and the formation process of cross-linked structures, in the synthesis of poly(methylsiloxane). Poly(methylsiloxane) was synthesized by cationic ring-opening polymerization of the cyclic monomer 1, 3, 5, 7-tetramethylcyclotetrasiloxane. A series of polymers were obtained by varying polymerization times. The initial and maximum decomposition temperatures increase to higher polymerization time until constant values are reached. At short polymerization time mainly linear polymers are formed with small fraction of cross-linked structures. At higher polymerization time partial and total cross-linked polymers are obtained. Formation of cross-linked structures stabilizes thermically the whole polymeric matrix, being the stability proportional to the cross-linking degree. The thermogravimetric analysis allowed us to formulate a method to determine the cross-linking degree of these polymers. FT-IR analysis showed the existence of the absorption band of variable intensity, corresponding to the vibration of the Si-H bond, in all the studied polymers. FT-IR spectra of the residual ceramic powder obtained by pyrolysis showed the typical absorption bands of these materials. The characterization of the polymers was also carried out by thermomechanical analysis. Kinetic decomposition parameters such us pre-exponential factors, decomposition reaction orders and activation energies were determined by thermogravimetry.
Inclusion complex of the antiviral drug acyclovir with cyclodextrin in aqueous solution and in solid phase
Rossel, Carlos von Plessing;Sepúlveda Carre?o, Jacqueline;Rodríguez-Baeza, Mario;Alderete, Joel Bernabé;
Química Nova , 2000, DOI: 10.1590/S0100-40422000000600007
Abstract: complexation between acyclovir (acv), an antiviral drug used for the treatment of herpes simplex virus infection, and b-cyclodextrin (b-cd) was studied in solution and in solid states. complexation in solution was evaluated using solubility studies and nuclear magnetic resonance spectroscopy (1h-nmr). in the solid state, x-ray diffraction, differential scanning calorimetry (dsc), thermal gravimetric analysis (tga) and dissolution studies were used. solubility studies suggested the existence of a 1:1 complex between acv and b-cd. 1h-nmr spectroscopy studies showed that the complex formed occurs with a stoichiometry ratio of 1:1. powder x-ray diffraction indicated that acv exists in a semicrystalline state in the complexed form with b-cd. dsc studies showed the existence of a complex of acv with b-cd. the tga studies confirmed the dsc results of the complex. solubility of acv in solid complexes was studied by the dissolution method and it was found to be much more soluble than the uncomplexed drug.
Inclusion complex of the antiviral drug acyclovir with cyclodextrin in aqueous solution and in solid phase
Rossel Carlos von Plessing,Sepúlveda Carre?o Jacqueline,Rodríguez-Baeza Mario,Alderete Joel Bernabé
Química Nova , 2000,
Abstract: Complexation between acyclovir (ACV), an antiviral drug used for the treatment of herpes simplex virus infection, and beta-cyclodextrin (beta-CD) was studied in solution and in solid states. Complexation in solution was evaluated using solubility studies and nuclear magnetic resonance spectroscopy (1H-NMR). In the solid state, X-ray diffraction, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and dissolution studies were used. Solubility studies suggested the existence of a 1:1 complex between ACV and beta-CD. 1H-NMR spectroscopy studies showed that the complex formed occurs with a stoichiometry ratio of 1:1. Powder X-ray diffraction indicated that ACV exists in a semicrystalline state in the complexed form with beta-CD. DSC studies showed the existence of a complex of ACV with beta-CD. The TGA studies confirmed the DSC results of the complex. Solubility of ACV in solid complexes was studied by the dissolution method and it was found to be much more soluble than the uncomplexed drug.
La ense?anza de las ciencias de la información en el currículum de los estudiantes de medicina y de otras especialidades afines
Nodarse Rodríguez,Mario;
ACIMED , 2005,
Abstract: in order to determine the present tendencies toward the incorporation of the teaching of information science to the curriculum of the medical students and other related specialties, it was made a review of the literature available in the biomedical databases -bibliographical or complete text style- and of multiple web sites with information related to the theme, starting from different search engines -general and thematic. the current world tendency is the information literacy to all the society, at all levels of eduation, especially at the university. an increasing importance is given to the introduction of courses or subjects on information sciences to the curriculum of the medical students and of other health professions at the world level. the curriculum design, in effect in cuba for the career of medicine and other related disciplines, lacks a program, subject or course that contributes to the knowledge and creation of the necessary skills among the students of these disciplines to use the resources and the information associated with their specialties.
DOS METONIMIAS DE NERUDA Y PARRA: EL BOLERO Y LA CUECA
Rodríguez,Mario;
Revista chilena de literatura , 2011, DOI: 10.4067/S0718-22952011000200008
Abstract: "la cueca" and "el bolero" are musical forms proposed as metonymies of a poetic prosody and syntax in neruda's veinte poemas de amor y una canción desesperada, and in parra's la cueca larga and artefactos. this work focuses mainly on the rhythmic and melodic substance of the verses, thus surpassing a division between language and music.
OíR Y NO LEER A BOLA?O "LA ENTONACIóN ORAL DE LA PROSA"
Rodríguez,Mario;
Universum (Talca) , 2009, DOI: 10.4067/S0718-23762009000200009
Abstract: this research suggests that spoken language, the oral mode used to narrate los detectives salvajes, with the strategies pertaining naturally to orality such as ellipsis, innuendo and anacoluthon, produces the basic structural mechanisms of the novel and helps to make it bola?o?s best work. the novel can be imagined as a laboratory in which a dual experiment is being conducted: the listening to a story that can be written/ the writing of a story that can be recited. the above proposition de-ritualizes the act of reading. the experiment is based on the fact that the simulation of oral production in the writing, when it functions together with what is inherent to it (major innuendoes between the speaker and the listener) produces a tension that is never dispelled, which captures the reader, who has occupied the place of the listener, with multiple conjectures that are impossible to resolve. the most important of these refers to evil. are its origins contingent or causal? thus it is that the riddle and its inseparable partner, the sphinx (cesárea tinajero, in this case) provide the novel with one of its key dimensions, that of a great mediation on evil.
The diplomatic battle between Beijing and Taipei in Central America and the Caribbean
Mario Esteban Rodríguez
Revista CIDOB d'Afers Internacionals , 2008,
Abstract: Half of the 23 countries that maintain official diplomatic relations with Taiwan are in Central and South America. One of the main objectives of China’s growing presence in this region is to achieve diplomatic recognition from these countries. This article examines the factors that are taken into consideration by Latin American and Caribbean countries when deciding whether to establish official diplomatic relations with China or with Taiwan. In this analysis,the author claims that over the short-term, there will not be a rapid, sharp drop in the number of Taiwan’s political allies in the region, in spite of the fact that Costa Rica decided to establishdiplomatic relations with Beijing in June 2007.
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