Browsing by Autor "Meribary Monsalve"

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    Evaluación de la actividad de complejos de samario(III) con ácido L-aspártico, ácido L-glutámico, glicina y o-fenantrolina, como iniciadores en la polimerizacion de carbonatos cíclicos
    (Universidad de Los Andes, 2016) Meribary Monsalve; Jesús Contreras; Eduardo Cardozo; R. Contreras
    Se estudió el comportamiento catalítico del acetato de samario (III) (SmOAc) y varios complejos de samario (III) tipoSm(o-phen)(Ln)3 (o-phen = orto-fenantrolina, L1 = ácido L-aspártico; L2= ácido L-glutámico y L3 = glicina), comoiniciadores en la polimerización de los carbonatos cíclicos trimetilén carbonato (TMC), 1-metil-trimetilén carbonato(MTMC) y el 2,2-dimetil-1,3-trimetilén carbonato (DMTC). Los resultados obtenidos indican que la actividad de losiniciadores depende fuertemente del aminoácido enlazado al átomo de samario (III). Los productos obtenidos fueroncaracterizados mediante espectroscopia de resonancia magnética nuclear y cromatografía de exclusión por tamaño. Losresultados de RMN-1H indican que la polimerización por apertura de anillo procede a través de un mecanismo decoordinación inserción con la ruptura selectiva del enlace acil-oxígeno.
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    Ring-opening copolymerization of (R,S)-β-butyrolactone and ε-caprolactone using sodium hydride as initiator
    (Budapest University of Technology and Economics, 2010) Meribary Monsalve; Jesús Contreras; E. Laredo; Francisco López‐Carrasquero
    Copolymers of racemic -butyrolactone ((R,S)-BL) and -caprolactone (CL), were synthesized by ring-opening polymerization initiated by sodium hydride (NaH). The initiator exhibited a satisfactory catalytic activity, producing copolymers whose yields are greatly influenced by the feed monomer ratio, CL/BL. All polymers obtained were characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and wide angle X-rays scattering, WAXS. The molar composition of copolyesters determined by 1 H-NMR spectra, showed that the incorporation of CL is favoured over the incorporation of (R,S)-BL. Gel permeation chromatography and 13 C-NMR spectra indicated that CL/BL copolymers had block sequence distribution. The TGA analysis of copolymers showed that these copolymers are stable up to temperatures near 200C, followed by a decomposition process in two steps; the first one is attributed to the (R,S)-BL block degradation and the second to the remaining PCL block. The crystallization process of these copolymers was studied by DSC and WAXS showing that the amorphous (R,S)-BL segments chains did not affect the crystallinity of the PCL blocks.