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Group 4 Metal Complexes of Phenylene–Salalen Ligands in rac ‐Lactide Polymerization Giving High Molecular Weight Stereoblock Poly(lactic acid)
Author(s) -
Stopper Ayellet,
Rosen Tomer,
Venditto Vincenzo,
Goldberg Israel,
Kol Moshe
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201701007
Subject(s) - tacticity , polymer chemistry , lactide , copolymer , polymerization , imine , polymer , chemistry , amine gas treating , differential scanning calorimetry , monomer , condensation polymer , phenylene , materials science , organic chemistry , catalysis , physics , thermodynamics
Phenylene–salalens—sequential tetradentate dianionic {ONNO}‐type ligands that include an ortho ‐phenylene group bridging between an imine and amine internal donors bound to phenol arms with a broad variety of substitution patterns are described. Zirconium and hafnium complexes of the type [{ONNO}M(O‐ t Bu) 2 ] were formed as single diastereomers, which, according to crystallographic structures, featured the fac (around the amine)‐ mer (around the imine) wrapping mode. The reactivity and stereoselectivity in rac ‐lactide ( rac ‐LA) polymerizations were found to depend on the substitution pattern: complexes featuring small groups on the imine‐side phenol and bulky groups on the amine‐side phenol exhibited the favorable combination of high activity and high isoselectivity ( P m ≤0.91). Isotactic stereoblock copolymers of high molecular weights were prepared. The polymers crystallized in the stereocomplex phase according to thermal (differential scanning calorimetry) and crystallographic analysis.