Suppressing Cyclic Polymerization for Isoselective Synthesis of High-Molecular-Weight Linear Polylactide Catalyzed by Sodium/Potassium Sulfonamidate Complexes

Abstract

A new sodium/potassium crown ether complex system with a series of bichelating sulfonamides as ligands was developed for the ring-opening polymerization (ROP) of rac-lactide. In this system, the side reaction of cyclic polymerization can be suppressed very well because of very different ROP rates initiated by BnOH and sulfonamide anion. The synthesis of high molecular weight linear polylactide with molecular weight high up to 107 kg/mol was successful. The best isoselectivity also can reach to a high value of P m = 0.84. The NMR analysis of the reaction mixture of rac-lactide and complex 3 together with kinetic studies suggests the mechanism of ROP in the absence of alcohol is a coordination–insertion mechanism. After addition of BnOH, the ROP rate can increase remarkably due to the cooperation interaction of alcohol and complex 3.

Tetradentate iminophenolate copper complexes in rac-lactide polymerization

“…show the same general polymerization behaviour as 1-5 ( Fig. 9, Tables 2 and S1, entries [42][43][44]. Coordination/dissociation of the 3 rd amino group is thus not responsible for the existence of two active species.…”

“…In a series of excellent publications, Wu and coworkers employed this concept in lactide polymerizations with phenolate complexes of group 1 metals, mostly sodium and potassium. 36, [39][40][41][42][43][44] They could show that phenolate is not incorporated in the polymer chain and acts (mostly) as spectator ligand. The bulky environment (crown-ether coordination around the metal center, highly substituted phenolates) constricts the environment sufficiently to allow stereocontrol, remarkably toward isotactic PLA.…”

Synthesis of lactide/ɛ‐caprolactone quasi‐random copolymer by using rationally designed mononuclear aluminum complexes with modified β‐ketiminato ligand

“…So far, a great variety of organometallics have been used as the catalysts for polymerizations of LA and ɛ ‐CL, which range from traditional stannous catalysts to main group catalysts (Na,Mg, Al, and Ca) and transition metal (Zn and Ti) as well as rare earth catalysts . Nonetheless, seldom catalysts can strictly produce random copolymer poly(LA‐ r ‐CL), with the approximately equal in average length of lactidyl and caproyl sequence ( L LA = L CL = 2) .…”

Ring-opening polymerization of rac-lactide catalyzed by crown ether complexes of sodium and potassium iminophenoxides

“…93 Recently Wu and co-workers reported that crown ether complexes of sodium and potassium mono-phenoxides exhibited high catalytic activity and high iso-selectivity for the ROP of rac-lactide. [94][95][96][97][98][99][100][101] However, the phenoxide ligands are required to have very bulky ortho-substituents on the aromatic rings to achieve good selectivity. [94][95][96][97][98][99][100][101] It is interesting to design simpler ligands to get high catalytic selectivity of complexes.…”

“…A plausible reason could be the presence of transesterication side reaction in the process of polymerization. [94][95][96][97][98][99][100][101] The relatively wide molecular weight distributions (1.18 to 1.39) and MALDI-TOF MS analysis ( The sodium and potassium complexes 1 and 4 were selected for a more detailed study on their catalysis. At rst, higher monomer loadings were tested using 1/BnOH and 4/BnOH, respectively (Table 1, entries 8-11 and 14-17).…”