1H NMR Spectroscopy in the Analysis and Characterization of Poly(lactide)

Abstract High resolution 500 MHz 1H NMR spectroscopy is a powerful tool for the analysis and characterization of poly(lactide) (PLA). It accurately provides information about the distribution of a few stereosequences in the polymer whose resonances are well-resolved in the NMR spectrum. Here, the splitting of the methine resonance due to coupling to the methyl protons in the polymer is removed by homonuclear decoupling. 13C NMR provides complementary stereosequence information, but due to the poor signal-to-noise ratio its accuracy is not comparable to that of 1H NMR. Through the analysis of the stereosequence distribution in a number of PLA spectra, it was determined that there is a preference for syndiotactic addition during lactide stereo copolymerization. It was shown that the normalized intensity of a few well-resolved resonances in the 1H spectrum of PLA can be used to quantitatively determine the lactide stereoisomer composition incorporated in the polymer. The change in stereosequence distribution...