Effect of the phenyl ring substituent on stereoselectivity in the ring-opening polymerization of the rac-lactide initiated by salen aluminum complexes

Abstract

A number of unreported salen aluminum complexes bearing Schiff base ligands starting from (R,R)-1,2-diammoniumcyclohexane mono-(+)-tartrate salt were synthesized. These complexes were characterized by 1 H, 13 C NMR, and elemental analysis. These complexes were employed as initiators for the ring-opening polymerization (ROP) of Llactide and rac-lactide. Complex 3 (R = Br) showed the highest activity for the ROP of L-lactide among these complexes, and complex 2 (R = i Pr) possessed the highest stereoselectivity for the ROP of rac-lactide among these aluminum isopropoxides. The kinetics studies of the polymerization employed complex 2 as initiator indicated that the polymerization rate was first-ordered in lactide and initiator.

Electron rich (salen)AlCl catalysts for lactide polymerisation: Investigation of the influence of regioisomers on the rate and initiation efficiency

“…Bulky electron-donating ortho-substituents (e.g. t Bu) typically display reduced activities but improved stereocontrol, [11,26,[44][45][46][47] whereas electron-withdrawing groups (e.g. Cl) generally increase the activity but reduce stereocontrol.…”

Nanoporous PLA/(Chitosan Nanoparticle) Composite Fibrous Membranes with Excellent Air Filtration and Antibacterial Performance

“…Most of them are petroleum-based polymers, the application of which has been found to coincide with serious environmental pollution. Additionally, fossil resources are gradually being depleted [19].…”

Cooperative Heterometallic Catalysts for Lactide Ring-Opening Polymerization: Combining Aluminum with Divalent Metals

“…Previously reported Al-salen catalysts have been tested under a range of conditions, with reported kobs values typically ranging from 1.9 x 10 -6 to 6.9 x 10 -3 s -1 . 19,20,28,35,63,[69][70][71][72] While the different conditions limit direct comparison, to the best of our knowledge the incorporation of Mg within complex C1c gives the fastest (salen)Al-chloride catalyst reported for rac-LA ROP to date (kobs = 8.8 x 10 -3 s -1 , Figures S55 and S56). While these heterometallic (salen)Al catalysts are Entry Catalyst Time (min) % Conversion [b] Mn,calc / Da [c] Mn,obs / Da [d] Ɖ [d] 1 S64, Table S4), and provide insight into the features underpinning heterometallic cooperativity.…”