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Polymorphous Crystallization and Multiple Melting Behavior of Poly(l-lactide): Molecular Weight Dependence

Macromolecules2007Vol. 40(19), pp. 6898–6905

Citations Over TimeTop 1% of 2007 papers

Pengju Pan, Weihua Kai, Bo Zhu, Tungalag Dong, Yoshio Inoue

Abstract

The effect of molecular weight (MW) on the polymorphous crystallization and melting behavior of poly(l-lactide) (PLLA) were systemically studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), and time-resolved Fourier transform infrared (FTIR) spectroscopy. It was found that the polymorphism of PLLA is not influenced much by MW, and the α‘- and α-form crystals are produced at low and high crystallization temperature (Tc), respectively, regardless of the MW. However, MW significantly affects the crystallization kinetics, and the crystallization rate reduces greatly with MW increasing. Moreover, the Tc- and MW-dependent melting behavior of PLLA was clarified with combining the DSC and FTIR results. It was found that the α‘- to α-crystalline phase transition occurs prior to the dominant melting in both the low- and high-MW PLLA crystallized at low Tc. Unlike the high-MW PLLA, in low-MW PLLA crystallized at low Tc, the α‘-form crystals only partially transform into the α-one, and some amounts of α‘-form crystals melt directly without transition during the heating process. With increasing Tc, the melting of PLLA with various MWs changes from the phase transition + melting mechanism to the usual melt−recrystallization mechanism.

Citations Over TimeTop 1% of 2007 papers

Abstract

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