Uniting Group-Transfer and Ring-Opening Polymerization-Block Copolymers from Functional Michael-Type Monomers and Lactones

Herein, the consecutive group-transfer polymerization (GTP) of the Michael-type monomer 2-vinylpyridine (2VP) and ring-opening polymerization (ROP) of epsilon-caprolactone (CL) or (-)-menthide (M) using a monometallic and a bimetallic 2-methoxaminethylamino-bis(phenolate) yttrium catalyst for the synthesis of AB- and BAB-type block copolymers (P2VP-b-PCL and P2VP-b-PM) are reported. Using the more demanding (-)-menthide, further insights into the catalytic nature of this combinatorial polymerization approach were gained using a kinetic copolymerization approach. These investigations revealed a living-type polymerization, for the initial GTP sequence as well as the subsequent ROP. To show the influence of the coordination strength of the monomers to the metal center, the addition sequence is alternated, uncovering a lower coordination strength of Michael-type monomer 2VP to the metal than that of lactones. Quenching of the active propagating chain end during ROP chain growth showed a coordination-insertion mechanism for the polymerization of CL and M initiated by an acyl-oxygen cleavage of lactones by the active P2VP chain. The AB- and BAB-type block copolymers of P2VP with PCL or PM showed the formation of precisely defined micelles in an acidic medium, and thermal transitions of the copolymers were shown to be microphase separation-influenced.