Structural Changes and Crystallization Dynamics of Poly(L-lactide) during the Cold-Crystallization Process Investigated by Infrared and Two-Dimensional Infrared Correlation Spectroscopy

摘要

The structural evolution and crystallization dynamics of poly(L-lactide) (PLLA) during isothermal cold-crystallization process are studied by infrared (IR) spectroscopy and two-dimensional correlation analysis.In the C=O stretching region,the band shift to a higher wavenumber taking place during the crystallization of PLLA is attributed to the dipole-dipole interaction between the C=O groups.A detailed analysis is performed for the range of 1500-1000 cm~(-1) where bands are highly overlapped.It was found that the 1458 cm~(-1) band reflects the structural order of the CH_3 group,and the band at 1109 cm~(-1) is related to the C-O-C trans conformation in the crystalline phase of PLLA.The band at 1193 cm~(-1) is sensitive not only to the structural adjustment of the C-O-C backbone but also to the structural order of CH_3 group in crystalline phase.From the analysis of the difference spectra and 2D correlation spectra in the 1500-1000 cm~(-1) region,it is shown that the structural adjustment of the CH_3 group unambiguously precedes that of the ester group.Moreover,the detailed crystallization kinetic of PLLA is investigated by analyzing difference spectra.