鏡像聚乳酸結晶螺旋形態之旋性控制與同掌性訊息之傳遞

Helical Morphologies of Enantiomeric Polylactides in Crystalline Phases with Homochiral Evolution

江振宏(Chen-Hung Chiang)

指導教授 ： 何榮銘

國立清華大學/工學院/化學工程學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00227

摘要

Herein, we aim to examine the forming mechanisms of banded spherulite (the presence of concentric rings or extinction bands under polarizes light microscope (PLM) observations) with exclusive optical activity (i.e., phase chirality) in crystallized chiral polylactides through chirality transfer on different length scales. The molecular chirality and conformational chirality of enantiomeric chiral polylactides are identified from circular dichroism (CD) spectra and vibrational circular dichroism (VCD) spectra, respectively. The optical activity of molecular chirality from lactic acid is affected by the formation of a helical conformation because of the transfer of chirality via intramolecular chiral interaction. The conformational chirality of the chiral polylactides is determined from the signiture of split-type Cotton effect in the absorption bands of ester group (C=O stretching) in the VCD spectrum at which one-handed helical chain conformation of the chiral polylactide can be found, indicating the chirality transfer from molecular chirality to conformational chirality. Owing to the crystalline lamellar twisting resulting from imbalanced stresses of folding surfaces, banded spherulites can be found in crystallized chiral polylactides and the sense of the lamellar twisting can be determined using PLM. Significant induced VCD signals in the absorption bands of the C-O-C vibration appear in the crystallized chiral polylactides, and exclusive optical activity can be identified. On the basis of the VCD and POM results, a homochiral evolution from the helical polymer chain (conformational chirality) to the lamellar twisting in the banded spherulite (phase chirality) is suggested via intermolecular chiral interaction. Furthermore, the formation of stereocomplex from blending of enantiomeric chiral polylactides is examined. In contrast to the intrinsic chiral polylactides, no banded spherulites can be found in the chiral polylactide blends with stereocomplex formation, consisting to the morphologies observed by scanning electron microscope and transmission electron microscopy. On the basis of morphological results, no occurrence of lamellar twisting can be found in stereocomplex crystallites. Moreover, the spectra of the stereocomplex blends show VCD silence in both absorptions of C=O and C-O-C vibrations, suggesting the symmetric packing of chain conformations between L- and D-form sequences on the fold surface and the core of crystallites. As a result, we suggest that the formation of stereocomplex might affect the occurrence of imbalanced stresses, resulting in the symmetric conformation on fold surface and giving the releasing of imbalanced stresses.

關鍵字

螺旋 ； 結晶

並列摘要

Herein, we aim to examine the forming mechanisms of banded spherulite (the presence of concentric rings or extinction bands under polarizes light microscope (PLM) observations) with exclusive optical activity (i.e., phase chirality) in crystallized chiral polylactides through chirality transfer on different length scales. The molecular chirality and conformational chirality of enantiomeric chiral polylactides are identified from circular dichroism (CD) spectra and vibrational circular dichroism (VCD) spectra, respectively. The optical activity of molecular chirality from lactic acid is affected by the formation of a helical conformation because of the transfer of chirality via intramolecular chiral interaction. The conformational chirality of the chiral polylactides is determined from the signiture of split-type Cotton effect in the absorption bands of ester group (C=O stretching) in the VCD spectrum at which one-handed helical chain conformation of the chiral polylactide can be found, indicating the chirality transfer from molecular chirality to conformational chirality. Owing to the crystalline lamellar twisting resulting from imbalanced stresses of folding surfaces, banded spherulites can be found in crystallized chiral polylactides and the sense of the lamellar twisting can be determined using PLM. Significant induced VCD signals in the absorption bands of the C-O-C vibration appear in the crystallized chiral polylactides, and exclusive optical activity can be identified. On the basis of the VCD and POM results, a homochiral evolution from the helical polymer chain (conformational chirality) to the lamellar twisting in the banded spherulite (phase chirality) is suggested via intermolecular chiral interaction. Furthermore, the formation of stereocomplex from blending of enantiomeric chiral polylactides is examined. In contrast to the intrinsic chiral polylactides, no banded spherulites can be found in the chiral polylactide blends with stereocomplex formation, consisting to the morphologies observed by scanning electron microscope and transmission electron microscopy. On the basis of morphological results, no occurrence of lamellar twisting can be found in stereocomplex crystallites. Moreover, the spectra of the stereocomplex blends show VCD silence in both absorptions of C=O and C-O-C vibrations, suggesting the symmetric packing of chain conformations between L- and D-form sequences on the fold surface and the core of crystallites. As a result, we suggest that the formation of stereocomplex might affect the occurrence of imbalanced stresses, resulting in the symmetric conformation on fold surface and giving the releasing of imbalanced stresses.

並列關鍵字

helix ； crystalline

參考文獻

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