|SUGANUMA, KOTO - Tokyo University Of Agriculture & Technology|
|MATSUDA, HIRONORI - Teijin Pharma Limited|
|IWAI, MASAHIRO - Teijin Pharma Limited|
|NONOKAWA, RYUJI - Teijin Pharma Limited|
|ASAKURA, TETSUO - Institute Of Material Science|
Submitted to: Polymer Testing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2014
Publication Date: 6/12/2014
Citation: Suganuma, K., Matsuda, H., Cheng, H.N., Iwai, M., Nonokawa, R., Asakura, T. 2014. NMR analysis and tacticity determination of poly(lactic acid) in C5D5N. Polymer Testing. 38:35-39.
Interpretive Summary: Poly(lactic acid) (PLA) is a well known polymer derived from agricultural resources, such as sugarcane, corn starch, and tapioca products. A major determinant of the physical properties of PLA is tacticity. Tacticity has been shown to influence PLA mechanical properties, thermal stability, Tm, Tg, crystallinity, solution stability, and polymer degradability. Tacticity of PLA is usually measured with NMR spectroscopy using deuterochloroform as a solvent. However, many 1H and 13C peaks are still found to be overlapped when deuterochloroform is used as the NMR solvent. In this work deuterated pyridine was found to be an alternative solvent for NMR. Improved peak separation was obtained which enabled the methyl proton peaks to be assigned to the appropriate tetrad sequences for the first time. An improved understanding of the NMR spectrum of PLA has the potential advantage of enabling PLA tacticity to be measured more quickly and more accurately and is especially useful for polymer synthesis and quality control.
Technical Abstract: In this work tacticity assignments of poly(lactic acid), (PLA), are reported for the NMR peaks from CH carbon and CH3 proton at the tetrad level in deuterated pyridine. The methyl protons are better resolved in pyridine due to solvent effects such as ring current shielding of the aromatic ring and electric field effect from the nitrogen lone pair. As an aid for the tacticity assignments, two-dimensional NMR spectra of poly(DL-lactic acid) (L/D=50/50) and relative intensities of PLA samples have been used. The new assignments provide a more detailed understanding of the 1H and 13C NMR spectra of PLA.