Transesterification, ring-opening polymerization catalysts

Lipase Transesterification and direct esterification (inch polyester synthesis) Ring-opening polymerization of 8-caprolactone Hydrolysis alcoholysis acetylation Higher stability of enzyme greater activity catalyst recyclable sometimes higher enantio- and regio-selectivity compared with VOCs... 

For transesterification of ethyl acetate with various alcohols promoted by mixed organotin oxides, more detailed studies have been carried out on the structure and catalytic properties of supported tin dichloride and trichloride precursors, and on mixed organotin oxides of the type [P—(CH2) —SnBuCl]20. " " It was found that ring opening polymerization of e-caprolactone using the supported mixed organotin oxide, in the presence of propanol, required lengthy spacers (11 carbon atoms was found to be the best) between the polystyrene matrix and tin, in order to avoid the collapse of the resin beads (as observed for a six carbon spacer). The tin contamination could be reduced to <5 ppm in the final products when these types of catalysts were used in the transesterification of ethyl acetate and various alcohols. " ... 

Other step-polymerization reactions of large cyclic monomers by entropically driven ring-opening polymerization have been reviewed (Hall and Hodge, 1999). An important example is the heating of cyclic bisphenol-A carbonates over a titanium isopropoxide transesterification catalyst to yield a polycarbonate with a relative molar mass of about 250000. This has also been performed under conditions of reaction injection moulding (Hall and Hodge, 1999). 

Appropriate macrodiols are produced via ring opening polymerization of cyclic diesters or lactones initialized by low molecular weight diols (see Fig. 16.4). The sequence structure of cooligomers can be influenced by application of a transesterification catalyst. The molecular weight of the oligomers can be controlled by the monomer/initiator ratio. Typically, the molecular masses Mn being obtained are between 500 g mol and 10 000 g mol T The net... 

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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