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NMR Analysis of Poly(Lactic Acid) via Statistical Models
Koto Suganuma1, Tetsuo Asakura2, Miyuki Oshimura3
1Material Analysis Research Center, Teijin Ltd, Hino, Tokyo 191-8512, Japan. ko.suganuma@teijin.co.jp.
Polymers
|April 24, 2019
Summary
Investigating poly(lactic acid) (PLA) tacticity using NMR spectroscopy revealed deviations from standard models. A new two-state model accurately quantifies transesterification and racemization during PLA polymerization.
Area of Science:
- Polymer Chemistry
- Spectroscopy
- Materials Science
Background:
- Poly(lactic acid) (PLA) properties depend on stereochemical arrangement.
- Nuclear Magnetic Resonance (NMR) spectroscopy is key for studying PLA tacticity.
- Previous studies utilized pair-addition Bernoullian models for PLA NMR data analysis.
Purpose of the Study:
- To analyze PLA tacticity using NMR spectroscopy.
- To investigate deviations from existing models in PLA polymerization.
- To develop an improved model for quantitative analysis of polymerization mechanisms.
Main Methods:
- Preparation of poly(lactic acid) (PLA) samples using varying ratios of L,L-lactide and D,D-lactide with a tin catalyst.
- Analysis of NMR spectroscopic data, specifically tetrad intensities.
- Fitting NMR data to pair-addition Bernoullian and a newly formulated two-state model.
Main Results:
- Observed NMR data showed significant deviations when analyzed with the standard pair-addition Bernoullian model.
- Deviations were attributed to transesterification and racemization during polymerization.
- The proposed two-state model (incorporating pair-addition and single-addition Bernoullian components) provided a superior fit to the experimental data.
Conclusions:
- The standard pair-addition Bernoullian model is insufficient for accurately describing PLA tacticity under certain polymerization conditions.
- The developed two-state model offers a quantitative method to assess transesterification and racemization.
- This approach provides valuable insights into the underlying mechanisms of poly(lactic acid) polymerization.
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