High-resolution 500 MHz solution-state 1H and 13C NMR spectra of various poly(lactides) indicate at least hexad stereosequence sensitivity. The poly(lactides) were prepared in vials by melt polymerization of various combinations of l-lactide, d-lactide, and meso-lactide at 180 °C for 3 h using tin(II) bis(2-ethylhexanoate) (tin(II) octoate) as the catalyst in a 1:10 000 ratio. The intensity distribution of the various stereosequence resonances in the NMR spectra indicates a preference for syndiotactic addition during the polymerization process. Minimal evidence of transesterification was observed for these polymerization conditions.

Solid-state 13 C CP-MAS NMR spectroscopy has been used to investigate highly crystalline, partially crystalline, and amorphous poly(L-lactide) (PLLA). The amorphous domains have broad resonances with Gaussian line shapes, while the crystalline domains have narrower resonances with a high degree of Lorentzian character. Spectra of highly crystalline PLLA have at least five distinct resonances for the carbonyl and methine functional groups in the polymer, indicating five or more crystallographically inequivalent sites in the crystalline domains of the polymer. For the amorphous polymer, broad Gaussian peaks are observed for each of the methyl, methine, and carbonyl functional groups. Spectra of partially crystalline PLLA contains spectral features of both domains, and furthermore, the spectra appear to be sensitive to both short range (nanometer) and long range (micrometer) order within the polymer. A method to extract the information of crystallinity and morphology from the solidstate CP-MAS NMR spectra of partially crystalline PLLA is discussed.

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