Ring-opening polymerization organic catalysts

As an alternative approach, polycarbosilanes 2.31 bearing pendant zirconocene moieties have also been prepared by ring-opening polymerization of the spirocyc-lic monomer 2.30 (Eq. 2.13) [62], In this case, the materials were structurally characterized, but the soluble fraction was of low molecular weight (M < ca. 3000) and the high molecular weight fraction was insoluble in organic solvents. In the presence of activators, both fractions functioned as ethene polymerization catalysts with moderate activity [62]. 

A last example to be mentioned here is the case of peculiar abnormal NHC (143) in which the carbene centre is no longer located between the nitrogen atoms but between nitrogen and carbon atoms. Compound (143) has been established as an efficient organocatalyst for ring-opening polymerization of cyclic esters.This report represents the first use of an abnormal NHC as catalyst in an organic transformation. 

Myers, M. Connor, E. F. Glauser, T Mock, A. Nyce, G Hedrick, J. L. Phosphines Nucleophilic organic catalysts for the controlled ring-opening polymerization of lactides. 7. Polym. ScL, Part A Polym. Chem. 2002,40,844-851. 

For example Kumar, A., and Gross, R. A., 2000, Candida antarctica Lipase B-Catalyzed Transesterification New Synthetic Routes to Copolyesters. J. Am. Chem. Soc. 122 11767-11770 Kumar, A., and Gross, R. A., 2000, Candida antartica lipase B catalyzed polycaprolactone synthesis effects of organic media and temperature. Biomacromolecules 1 133-138 Kobayashi, S, Uyama, H., Namekawa, S., and Hayakawa, H., 1998, Enzymic Ring-Opening Polymerization and Copolymerization of 8-Octanolide by Lipase Catalyst. Macromolecules 31 5655. 

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