Controlled Ring-Opening Polymerization of ϵ-Caprolactone Using Polymer-Supported Scandium Trifluoromethanesulfonate in Organic Solvent and Ionic Liquids

Abstract

In this article, we described the ring-opening polymerization (ROP) of ϵ-caprolactone using a polymer-supported scandium(III) trifluoromethanesulfonate [Sc(OTf)3] catalyst (PS−Sc) under mild conditions. In this system, it is possible to synthesize poly(ϵ-caprolactone) PCL (Mn = 4.1−10.8 × 103) with low polydispersity (Mw/Mn = 1.12−1.16). The Arrhenius equation was used to investigate the reaction kinetics. Furthermore, in two-step polymerization, the molecular weight increased without broadening of the molecular weight distributions. A plot of Mw/Mn versus conversion and the reaction time showed that Mw/Mn was constant during polymerization and had no relation to the increase of molecular weight. A plot of Mn versus conversion showed that Mn increased linearly as a function of conversion. These results indicate that PS−Sc catalyzed living polymerizations of ϵ-caprolactone as well as did Sc(OTf)3. After polymerization, the catalyst was easily recovered quantitatively, and no loss of Sc was observed after use. Next, we used ionic liquids instead of toluene, and found that [bmim][PF6] and [emim][PF6] accelerated the ROP of ϵ-caprolactone in this system. The ROP in some ionic liquids also made it possible to chemically modify cellulose using grafting from technique.