Ring-opening polymerization of ϵ-caprolactone initiated by rare earth complex catalysts

The polymerization of caprolactone (ϵ‐CL) was initiated by yttrium triisopropoxide {Y(OPir)3}, bimetallic isopropoxide of yttrium and aluminum {Y[Al(OPis)4]3}, yttrium and tin(II) {Y[Sn(OPir)3]3}, and tin(II) and yttrium {Sn[Y(OPir)4]2}, respectively. The polymerization was carried out through coordinative insertion of a monomer into the free metal‐oxygen bond. The molecular weight and yield of poly(ϵ‐caprolactone) (PCL) were affected drastically by the mol % of the initiator to the monomer (Co/Mo). The results showed that Y(OPir)3 and Sn[Y(OPir)4]2 were more effective than were {Y[Al(OPir)4]3} and {Y[Sn(OPir)3]3} for the polymerization of ϵ‐CL. When polymerization was conducted at 5°C using Y(OPir)3 as the initiator or at 10°C using Sn[Y(OPir)4]4 as the initiator, polymers with a molecular weight of 45.9 × 103 or 54.0 × 103 and high yield resulted in 30 or 5 min, respectively. The polymer was characterized by FTIR, H‐NMR, and GPC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1295–1299, 1997