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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Commodity Utilization Research » Research » Publications at this Location » Publication #361223

Research Project: Increasing the Value of Cottonseed

Location: Commodity Utilization Research

Title: NMR analysis of poly(lactic acid) via statistical models

item SUGANUMA, KOTO - Teijin Pharma Limited
item ASAKURA, TETSUO - Tokyo University Of Agriculture & Technology
item OSHIMURA, MIYUKI - Tokushima University
item HIRANO, TOMOHIRO - Tokushima University
item UTE, KOICHI - Tokushima University
item Cheng, Huai

Submitted to: Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2019
Publication Date: 4/19/2019
Citation: Suganuma, K., Asakura, T., Oshimura, M., Hirano, T., Ute, K., Cheng, H.N. 2019. NMR analysis of poly(lactic acid) via statistical models. Polymers. 11(4):725.

Interpretive Summary: Poly(lactic acid)(PLA) is a well-known agro-based and biodegradable polymer that has found many applications in industrial, biomedical, therapeutic, and pharmaceutical areas. Because the properties of PLA depend strongly on its stereochemical structure, it is helpful to use NMR to study the polymer structure. Commercially PLA is often made with tin alkanoate catalysts, but complications can occur that cause complex distributions of stereochemical structures. In this work, we first analyzed the NMR data with a commonly accepted reaction model, which did not fit the observed data very well. We then introduced a new model, which produced a noticeably better fit with the data. In this way, an improved analysis of the NMR data is achieved, and the stereochemistry of PLA can be better understood. The results should benefit PLA manufacturers and users as they seek to obtain a more useful NMR method to study PLA.

Technical Abstract: The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data had been 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.