Crystallization behavior of stereoblock polylactide with high sequence regularity structure

Stereoblock polylactide (Sb-PLA) was prepared via a consecutive method by ring-opening polymerization and its stereocomplex crystallization behavior was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM). The molecular weight, sequence structure of anisotropic segments of Sb-PLA and crystals structure were characterized by using GPC, H-1 NMR, C-13 NMR and XRD. The Sb-PLA with bonding a higher stereoregularity chains prepared by the synthesis route exhibited a higher melting point and uniquely stereocomplex crystallization behavior compared with the Sb-PLA prepared by commonly reported method. The isothermal crystallization results indicated that the crystallization temperature of Sb-PLA's increased about 20 degrees C higher than reported Sc-PLA materials. Moreover, crystallization rate constant (K) and crystallization activation energy (Delta E) expressed by the Arrhenius equation demonstrated that Sb-PLA presents a higher crystallization rate. The data of isothermal crystallization experiments were analyzed based on Lauritzen-Hoffman (LH) theory, crystallization rate constant (G(0)), nucleation constant (K-g), fold surface free energy (sigma(e)), and folding work (q) were estimated to be 1.5 x 10(27) mu m/min, 1.2 x 10(6) K-2, 113.0 erg/cm(2) and 8.20 x 10(-21) J, respectively. These results indicated that Sb-PLA chains with a higher stereoregularity suggested to be the main factor accounting for the formation unique stereocomplex crystals.