Group 4 Metal Complexes of Phenylene–Salalen Ligands in rac‐Lactide Polymerization Giving High Molecular Weight Stereoblock Poly(lactic acid)

Abstract

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-tBu) ] 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 ≤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.

Ring-opening polymerisation of l- and rac-lactide using group 4 permethylpentalene aryloxides and alkoxides

“…6) 67 and to some zirconium complexes bearing phenylene-salalen ligands where up to 99% conversion was achieved after 24 hours at 70°C with [LA] 0 /[M] 0 of 300. 68 In contrast to the ROP of L-lactide, 2 shows a faster rate of polymerisation than 3 for the ROP of rac-lactide, which suggests that 2 may have a more preferential ligand environment for D-lactide monomer insertion than 3. Similar to the polymerisation of L-lactide, 6 shows a slower rate of polymerisation than 2 and 3, which may be due to its increased steric bulk or the reduction in the number of aryloxide groups.…”

Iron(III) Salalen Complexes for the Polymerisation of Lactide

“…For this system, stereocontrol was dictated by aryl substituents with both chain end and enantiomorphic site control mechanisms being operational. Salalen complexes of other metals {Ti IV , Zr IV , Hf IV , Y III , Sm III and Nd III } have also been successfully applied to the ROP of lactide , . Recently, Lamberti and co‐workers have reported the first example of an Fe III salalen {Fe( 1 )Cl} .…”

Polymerization of rac‐Lactide Using Achiral Iron Complexes: Access to Thermally Stable Stereocomplexes

“…As imilar behavior for PLA stereoblocks obtained from rac-LA had already been observed by the groups of Nomura (whose data are also shown in Figure S16), Du, Chen, and Kol. [25] We also observed ac orrelation between the degree of stereoregularity and the glass-transition temperature.Indeed, al inear relationship between T g and P m is apparent in Figure 3. [26] An influence of polymer tacticity on T g was already shown for PLAs, [27] and T g values ranging from 34 8 8C and 49 8 8Cf or syndiotactic [28] and hetereotactic PLAs, [29] respectively,w ere described.…”