Ring-opening polymerization of ε-caprolactone by means of mono- and multifunctional initiators:: Comparison of chemical and enzymatic catalysis

Protected polyglycidols with a linear or star-shaped architecture were obtained via anionic ring-opening polymerization of protected glycidol in diglyme with potassium as counterion. Removal of the protecting groups lead to polyglycidols, which were used as multifunctional macroinitiators for the chemically and enzymatically catalyzed ring-opening polymerization of is an element of-caprolactone. For the chemically catalyzed polymerization zinc(II) 2-ethylhexanoate was used, while Novozyme 435 (Lipase B from Candida antarctica immobilized on a macroporous resin) was used for the enzymatically catalyzed polymerization. To determine the characteristics of the two differently catalyzed polymerizations, monofunctional macroinitiators based on poly(ethylene glycol) were applied. The main difference observed was the initiator efficiency, which was explained by the different polymerization mechanism. By using multifunctional macroinitiators the difference in the initiation efficiency lead to different polymer architectures. For the chemically catalyzed polymerization, all hydroxy groups of the polyglycidols initiated polymerization, and core-shell polymers with a hydrophilic polyether core and a hydrophobic polyester shell were obtained. For the enzymatically catalyzed polymerization only 15-20% of the hydroxyl groups initiated the polymerization of is an element of-caprolactone with the result of a different polymer architecture; these polymers have a hydrophilic polyglycidol head coil with hydrophobic poly(is an element of-caprolactone) tails.