Living Ring Opening Polymerization of e-caprolactone Mediated by Lithium Silanolates

A.J. SATTI; A. FREITAS; M.A VILLAR; E.M. VALLÉS; C. GIACOMELLI; A.E. CIOLINO

Sitges

Simposio; Third International Symposium Frontiers in Polymer Science; 2013

Elsevier

Anionic ring-opening polymerization (AROP) of ε-caprolactone (ε-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, ε-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(ε-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 ε-CL ring was proposed in order to explain the mechanism for the AROP of the cyclic monomer.