Experimental (IR/Raman and 1H/13C NMR) and theoretical (DFT) studies of the preferential conformations adopted by L-lactic acid oligomers and poly(L-lactic acid) homopolymer.

ABSTRACT

L-Lactic acid (L-LA) oligomers (up to the pentamer) were studied by three complementary approaches vibrational (IR and Raman) and NMR ((1)H and (13)C) spectroscopies and DFT calculations. Vibrational and NMR spectra of L-LA oligomers and poly(L-lactic acid) (PLLA) homopolymer were recorded at room temperature and interpreted. Further insight into the structures (conformations) of the title systems was provided by theoretical B3LYP/6-311++G(d,p) studies. Calculated energies and computed vibrational and NMR spectra of the most stable conformers of L-LA oligomers, together with the experimental vibrational and NMR spectra, enabled the characterization of the preferred conformations adopted by PLLA chains.