Substitution effect on phenalenyl backbone in the rate of organozinc catalyzed ROP of cyclic esters

Abstract

A series of zinc complexes (1–6) supported by substituted phenalenyl ligands was synthesized by reacting the phenalenyl ligands with diethyl zinc under ethane evolution. The solid state structures of these complexes (1–6) were determined by single crystal X-ray crystallography. Furthermore, the organozinc complexes (4–6) were tested for the polymerization of cyclic esters as efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) and rac-lactide (rac-LA) in the presence of benzyl alcohol (BnOH) as initiator. Complex 4 exhibited remarkably higher rate of polymerization under identical reaction condition than complexes 5 and 6. The polymerization of ε-caprolactone produced polymer with narrow polydispersities (M_w/M_n = 1.06 to 1.22), while the polymerization of lactide monomers afforded polylactides with polydispersity values ranging from 1.08 to 1.8. The kinetic experiments unravelled a controlled polymerization. The controlled nature of polymerization was further utilized in the preparation of the block copolymer poly(CL)block-poly(rac-LA).