Ring‐opening polymerization of rac‐ and meso‐lactide initiated by indium bis(phenolate) isopropoxy complexes

Abstract

Ring-opening polymerization of rac-and meso-lactide initiated by indium bis(phenolate) isopropoxides {1,4-dithiabutanediylbis(4,6-di-tert-butylphenolate)}(isopropoxy)indium (1) and {1,4-dithiabutanediylbis(4,6-di(2-phenyl-2-propyl)phenolate)}(isopropoxy)indium (2) is found to follow first-order kinetics for monomer conversion. Activation parameters DH ‡ and DS ‡ suggest an ordered transition state. Initiators 1 and 2 polymerize meso-lactide faster than rac-lactide. In general, compound 2 with the more bulky cumyl ortho-substituents in the phenolate moiety shows higher polymerization activity than 1 with tert-butyl substituents. meso-Lactide is polymerized to syndiotactic poly(meso-lactides) in THF, while polymerization of rac-lactide in THF gives atactic poly(rac-lactides) with solvent-dependent preferences for heterotactic (THF) or isotactic (CH 2 Cl 2 ) sequences. Indium bis(phenolate) compound rac-(1,2-cyclohexanedithio-2,2 0 -bis{4,6-di(2-phenyl-2-propyl)phenolato}(isopropoxy)indium (3) polymerizes mesolactide to give syndiotactic poly(meso-lactide) with narrow molecular weight distributions and rac-lactide in THF to give heterotactically enriched poly(rac-lactides).

Transesterification in Alcohol‐Initiated ROPs of l‐ and meso‐Lactide Catalyzed by Sn(II) and Sn(IV) Compounds at Low Temperatures

“…The lower melting temperature of m ‐lactide/rac‐lactide mixture used in this work (40–44 °C) allowed for polymerizations at 80 °C and even at 60 °C in bulk. A mixture of m‐lactide with a smaller amount of rac‐lactide was not only desirable to lower the melting point, it was also favorable to achieve a nearly random stereo sequence, because neat m‐lactide may have a considerable tendency to generate syndiotactic blocks . At first, three ethanol‐initiated polymerizations were performed with a relatively high In/Cat ratio (10/1) to suppress intermolecular transesterification and thus, formation of odd‐numbered chains.…”

“…Additional polymerization experiments were performed with a higher catalyst concentration (In/Cat = 1.25/1,) to find out to what extent cyclization may occur in alcohol‐initiated ROPs of meso ‐lactide. In a previous study of alcohol‐initiated and SnOct 2 ‐catalyzed polymerizations of l ‐lactide no cyclization was observed at temperatures below 120 °C . Therefore, four analogous polymerizations of m ‐lactide were performed at 100 and 80 °C, and the time was varied from 22 to 44 h. The MALDI‐TOF mass spectra revealed the formation of cycles even at 100 °C and 22 h (Figure B).…”

High activity of an indium alkoxide complex toward ring opening polymerization of cyclic esters

“…2 Of the numerous pre-catalysts developed toward this end, indium complexes have demonstrated high activity and stereoselectivity for a number of monomers. [3][4][5][6][7][8][9][10][11][12][13] Lactide polymerizations have been particularly well examined, but many of the precatalysts [14][15][16][17][18][19][20] often require initiators. β-butyrolactone, 8,21 ε-caprolactone, 20 and trimethylene carbonate 22 polymerizations have also been achieved by indium catalysts.…”

Synthesis and characterization of rare-earth metal complexes supported by a new pentadentate Schiff base and their application in heteroselective polymerization of rac-lactide

“…The measured molecular weights (M n ) of the resulting polymers increased linearly with the monomer conversion and the molecular weight distribution (PDI) of the polymers kept almost unchange (1.02-1.09) (Fig. 4), indicating the polymerization of rac-LA initiated by complex 2 proceeds in a 85 living fashion at 0 ºC. °C.…”

“…The structures were solved by direct methods and refined by full-matrix least-squares procedures based on |F| 2 . The hydrogen 85 atoms in these complexes were generated geometrically, assigned appropriate isotropic thermal parameters, and allowed to ride on their parent carbon atoms. All of the hydrogen atoms were held stationary and included in the structure factor calculation in the final stage of full-matrix least-squares refinement.…”