Poly(L-lactide): XII. Formation, growth, and morphology of crystalline residues as extended-chain crystallites through hydrolysis of poly(L-lactide) films in phosphate-buffered solution

摘要

The poly(L-lactide) [i.e. poly(L-lactic acid) (PLLA)] films prepared by crystallization or annealing at different temperatures (T_as) were hydrolyzed at 97 ℃ in a phosphate-buffered solution (PBS) and changes in their long period (L), lamellae thickness (l_c), physical properties, and morphology were investigated by small angle X-ray scattering (SAXS), gel permeation chromatography (GPC), light-scattering (LS) measurements, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The L and l_c values of the PLLA films before hydrolysis and the l_c values of the crystalline residues after the hydrolysis for 40 h became higher with increasing T_a. The l_c values of the crystalline residues (extended-chain crystallites) after the hydrolysis, assuming that crystalline residues were composed solely of the crystalline regions, were found to be in complete agreement with the L values of the films before the hydrolysis and the l_c values were increased by the hydrolysis in PBS at 97 ℃ and also at 37 ℃. The reasons for the decreased melting temperature (T_m) after the hydrolysis despite the increased l_c are discussed.