INQUISUR   21779
INSTITUTO DE QUIMICA DEL SUR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Living Ring Opening Polymerization of e-Caprolactone Mediated by Lithium Silanolates.
Autor/es:
SATTI A.J.; FREITAS, A.G.; VILLAR, M.A.; VALLÉS, E.M.; GIACOMELLI, C.; CIOLINO A.E.
Lugar:
Sitges
Reunión:
Simposio; Frontiers in Polymer Science; 2013
Institución organizadora:
Elsevier
Resumen:
Anionic ring-opening polymerization (AROP) of epsilon-caprolactone (epsilon-CL) was performed by using lithium silanolates (LS) as initiators, and high vacuum techniques. LS were obtained by reaction between hexamethyl(cyclotrisiloxane) (D3) and freshly prepared sec - Bu-Li+, in a molar ratio equal to 1:1, in whole sealed reactors, under continuous stirring during 24 hs. After this first step, epsilon-CL monomer was added and the homopolymerization proceed during 24 hs. A narrow PCL homopolymer was obtained (Mn = 11,000 Da, PD = 1.14). In another experience, living poly(dimethylsiloxanil)lithium was employed as macroinitiator in order to obtain poly(dimethylsiloxane)-block-poly(epsilon-caprolactone) copolymer (PDMS-b-PCL) by sequential addition of monomers. In order to check the efficiency of the last synthetic procedure, another PDMS-b-PCL copolymer with similar composition was synthesized by conventional ring-opening polymerization (ROP) using tin(II) 2-ethylhexanoate as catalyst, and an anionic hydroxyl terminated PDMS as initiator. All the polymers obtained were subsequently characterized by size exclusion chromatography (SEC), 1H nuclear magnetic resonance (1H-RMN), and Fourier transform infrared spectroscopy (FTIR). According to the results, the LS are efficient initiators for the ROP of ε-CL monomer, which is an unexpected result as for the controlled living polymerization of methyl methacrylate mediated by LS previously reported by the group of Jérôme in 1998. A temperature-promoted nucleophilic attack of the macrosilanolate initiator to the carbonyl group of the e-CL ring was proposed in order to explain the mechanism for the AROP of the cyclic monomer.