Phosphines: Nucleophilic organic catalysts for the controlled ring-opening polymerization of lactides

A new metal-free synthetic approach to the controlled ring-opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)3, PhPMe2, Ph2PMe, PPh3, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α-end group upon ROP. A likely polymerization pathway is through a monomer-activated mechanism, with minimal active species, facilitating narrow molecular weight distributions.