Solid State 13C CP-MAS NMR Studies of the Crystallinity and Morphology of Poly(l-lactide)

Abstract

Solid-state 13C 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 solid-state CP-MAS NMR spectra of partially crystalline PLLA is discussed.