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.

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.

Abstract…………………………………………………………………...I
Contents………………………………………………………………....III
List of Figures……………………………………………………..……VI
Chapter 1 Introduction…………………………………………………1
1-1Chirality……………………………………………………………….1
1-2 Helical Conformation...........................................................................3
1-2.1 Helical persistent length and helical reversal..............................6
1-2.2 Majority rule versus sergeants and soldiers effect......................9
1-2.3 Helical inversion in polymer aggregation.................................11
1-3 Circular Dichroism.............................................................................14
1-4 Vibrational Circular Dichroism..........................................................17
1-5 Conjugated Coupling Rule and Exciton Chirality Method................18
1-6 CD and VCD Application for Studying the Chiral Molecular Self-assembly……………..………………………………………...21
1-7 Self-Assembly and Supramolecular Chemistry.................................26
1-8 Chiral Effect on Self-Assembly..........................................................35
1-9 Banded Spherulitic Morphologies......................................................43
1-10 Crystalline Behavior of Stereocomplex...........................................48
Chapter 2 Objectives..............................................................................52
Chapter 3 Experimental Details............................................................55
3-1 Materials.............................................................................................55
3-1.1 Synthesis of enatiomeric chiral polylactides………………….55
3-2 Preparation of Polymer Solution........................................................55
3-2.1 Preparation of polymer thin-film samples.................................56
3-3Characterization and Instruments.......................................................56
3-3.1 Circular dichroism spectroscopy (CD)......................................56
3-3.2 Vibrational circular dichroism spectroscopy (VCD).................56
3-3.3 Polarized light microscopy (PLM)............................................56
3-3.4 Differential Scanning Calorimetry (DSC).................................57
3-3.5 Small-angle X-ray (SAXS).......................................................57
3-3.6 Transmission Electron Microscopy (TEM)...............................57
3-3.7 Scanning Electron Microscopy (SEM).....................................58
Chapter 4 Results and Discussion.........................................................59
4.1 Intramolecular Chiral Interaction…………………………………...59
4-1.1 Molecular chirality examined by ECD…………………….…60
4-1.2 Conformational chirality examined by VCD………………....62
4-2 Intermolecular Chiral Interaction…………………………………...64
4-2.1 Intermolecular chiral interaction in solid state……………..…65
4-3 Crystalline Phases of PLLA and PDLA…………………………….68
4-3.1 Formation of banded spherulites……………………………...68
4-3.2 Thickness of lamellar twisting……………………………..…71
4-3.3 Handedness of banded spherulitic morphologies………..……74
4-3.4 Homochiral evolution………………………………………....76
4-4 Crystalline Morphologies of Stereocomplex in enantiomeric polylactides.........................................................................................79
4-4.1 Thermal behavior of stereocomplex………………………..…79
4-4.2 Crystalline morphologies of stereocomplex…………………..81
4-4.3 Chiral interaction of sterocomplex……………………………85
4-5 Peculiar Intermolecular Chiral Interaction for Polylactides in Solution...............................................................................................89
Chapter 5 Conclusions...........................................................................95
Chapter 6 Future Work..........................................................................97
Chapter 7 References.............................................................................99

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