Mechanistic study of Sn(Oct)2‐catalyzed ε‐caprolactone polymerization using Sn(Oct)2/BF3 dual catalyst

Abstract A novel method was used to investigate the mechanism of Sn(Oct) 2 ‐catalyzed ε‐caprolactone polymerization by using Sn(Oct) 2 /BF 3 dual catalyst. The bulk polymerization was conducted at 110 and 130°C with different Sn(Oct) 2 /BF 3 ratios. The polymerization kinetics was followed using gel permeation chromatography, and the molecular structures of the low‐molecular weight polymers were examined using 1 H‐nuclear magnetic resonance (NMR). A polymerization induction period was observed in polymerizations containing the Sn(Oct) 2 catalyst, but it was not observed in the system containing only BF 3 . After the induction period, BF 3 and Sn(Oct) 2 initiated the polymerization separately. For Sn(Oct) 2 catalyst with no purposely added alcohol, the actual initiation species is a tin hydroxide species formed in situ by the reaction of Sn(Oct) 2 and adventitious water. For BF 3 catalyst, the active species is the protonic acid formed by the reaction of BF 3 with the adventitious water. When mixed, the Sn(Oct) 2 reacts with the adventitious water faster than the BF 3 , preventing the BF 3 catalyzing any polymerizations during the induction period. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009