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Open AccessArticle

NMR Analysis of Poly(Lactic Acid) via Statistical Models

1
Material Analysis Research Center, Teijin Ltd, Hino, Tokyo 191-8512, Japan
2
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
3
Department of Applied Chemistry, Tokushima University, 2-1 Minamijosanjima, Tokushima 770-8506, Japan
4
Southern Regional Research Center, USDA Agricultural Research Service, 1100 Robert E. Lee Blvd., New Orleans, LA 70124, USA
*
Authors to whom correspondence should be addressed.
Polymers 2019, 11(4), 725; https://doi.org/10.3390/polym11040725
Received: 20 March 2019 / Revised: 15 April 2019 / Accepted: 16 April 2019 / Published: 19 April 2019
(This article belongs to the Special Issue NMR in Polymer Science)
The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the polymerization mechanism. View Full-Text
Keywords: Bernoullian; NMR; poly(lactic acid); statistical model; stereosequences; tacticity Bernoullian; NMR; poly(lactic acid); statistical model; stereosequences; tacticity
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Suganuma, K.; Asakura, T.; Oshimura, M.; Hirano, T.; Ute, K.; Cheng, H.N. NMR Analysis of Poly(Lactic Acid) via Statistical Models. Polymers 2019, 11, 725.

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