Thermodynamic and stereochemical aspects of the polymerizability of glycolide and lactide |
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Authors: | Carlos Alemán Oscar Bertran K N Houk Anne Buyle Padías and Henry K Hall |
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Institution: | (1) Departament d’Enginyeria Qu?mica, E.T.S. d’Enginyers Industrials de Barcelona, Universitat Polit?cnica de Catalunya, Diagonal 647, 08028 Barcelona, Spain;(2) Center for Research in Nano-Engineering, Universitat Polit?cnica de Catalunya, Campus Sud, Edifici C’, C/Pasqual i Vila s/n, 08028 Barcelona, Spain;(3) Departament d’Enginyeria Qu?mica, EUETII, Universitat Polit?cnica de Catalunya, P?a Rei 15, 08700 Igualada, Spain;(4) Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA;(5) Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA |
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Abstract: | The ring-opening polymerizations of the dilactones glycolide and the S,S- and S,R-stereoisomers of lactide were studied using quantum mechanical methods. The ring strain and the conformational distribution
of these cyclic monomers and of the polymers were calculated, and the effect of the medium on the polymerization was predicted,
for both bulk and solution. The polymerizability of the three monomers in the gas phase, that is, nonpolar medium, is much
greater than that of δ-valerolactone or 1,4-dioxan-2-one. This difference vanishes in the polar medium chloroform, which is
attributed to the fact that, while all of these monomers possess polar cis-lactone bonds, the three dilactones possess small
dipole moments. The data are combined to give polymerization enthalpy and free energy values. The four stereoregular lactide
polymers did not differ significantly in energy. Accordingly, the ability to synthesize any one of these rests on catalyst
specificity (“polymer chain-end control”). Although introduction of sterically demanding methyl groups into glycolide is expected
to favor coiled conformations and decrease polymerizability, this was not found to be the case. Good agreement of calculated
values with experimental data from the literature was achieved. |
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