Discrete yttrium catalysts for the controlled polymerization of cyclic esters

A discrete yttrium (III) catalyst was used to control the polymerization of lactide and caprolactone. The catalyst used is an alkoxo-bridged triyttrium (III) complex with a novel cluster structure that is retained in the solution. The cluster is capable of polymerizing both lactide and caprolactone in a controlled manner. The catalyst was modified by adding benzyl alcohol to a dimer. This leads to changes in the catalytic activity but does not disrupt the dimeric structure previously seen in either the solid or solution state.