The Second Block Copolymer Poly Peptide Synthesis And Self-assembly Film Structure

Polypeptide is a kind of biomacromolecules by amide linkage of amino acids. Based on the intramolecular or intermolecular hydrogen bonding, the molecular chain segments often form stable secondary structures such as α-helix or β-folding. The α-helical conformation suggests the rigid rod shaped feature, and it provides important research values in liquid crystalline field. In addition, the material properties and functions conferred by this structure has been a research topic of great concern by the researchers.In recent years, a large number of researchers maintain a high level of interest in regular arrangement structures in nanoscale self-assemblied from monodisperse, as well as low polymerization degree of copolypeptides materials. The commonly used N-carboxylic acid anhydride (NCA) living polymerization method is to synthesis the required polypeptide materials. However, the NCA method prone to chain transfer, chain termination, and chain break in a variety of side effects, therefore the molecular weight is difficult to be controlled, and it is difficult to obtain a narrow molecular weight distribution of polypeptides or copolypeptides. For this reason, the content of this study is to synthesis a kind of diblock copolypeptide, poly (y-benzyl-L-glutamic acid)-b-poly(y-dodecyl-L-glutamate)(PBLG-b-PDLG) with narrow molecular weight distribution of less than1.10. The synthesis method is similar to NCA method, but the synthetic condition is different in0℃low temperature and using n-hexyl amine as the initiator. For this new type of rod shaped diblock copolypeptide materials, we investigated their thermal properties, liquid crystal properties, as well as the self-assembled structures in films.By using the1H nuclear magnetic resonance (1H-NMR) and gel permeation chromatography (GPC) methods, in chapter2, we express the characterization of molecular structure and the relative molecular weight and distribution of the first block of PBLG-NH2and diblock copolymers PBLG-b-PDLGs. Because the molecular weight distribution (Mw/Mn) of PBLG-NH2and PBLG-b-PDLG are less than1.10, the side effects were restrained in the whole polymerization process, and the living activity was maintained. It concludes that the low temperature condition is conducive to the polymerization of low polydispersity materials. According to the’H-NMR spectra of a particular integral area ratio as well as the molecular weight of the first block, it infers the diblock copolymers with chemical components of PBLG27-b-PDLG30and PBLG29-b-PDLG45. Even the thermal behaviors are slightly different according to different components, two samples both exhibit weak thermotropic liquid crystalline nature by above100℃heating. In addition, the thermotropic liquid crystalline behavior of the two block copolymers is different from the random copolymer, which does not form helical structure of cholesteric liquid crystal phase. The explicit liquid crystalline nature could be observed in solution, and the fan-shaped texture explained the liquid crystalline molecules are in highly ordered smectic phase arrangement. Because the smectic structure is in orderly layered arrangement, this appearance is believed to be contributed by its narrow molecular weight distribution.Through the molecular alignment practices by electric and magnetic appliances, in Chapter3we describe the detailed self-assembled structures of PBLG-b-PDLG in single domain orientation. In order to understand the molecular packings and the self-assembly of diblock sides, we examine the detailed periodic structures of solid free-standing membranes prepared by solvent drying and under electric and magnetic alignment by using small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) method. The results showed that PBLG27-b-PDLG3o molecules pack in hexagonal pattern, and the sections of PBLG and PDLG two blocks appear alternatively along the molecular long axis. It means the molecules pack in head-to-head and form a double layered self-assembly structure in cycle. Because the molecular axis is parallel to the normal direction of the layer, the periodic length of the lamellar structure corresponds to the twice molecular length of PBLG27-b-PDLG3o, which is about180A. On the other hand, the PDLG45-b-PBLG29molecules arrange in tetragonal packing structure, and the molecules also oriented in head-to-head accumulation to form a double-layer structure. Unlike PBLG27-b-PDLG3o, the periodic structure with the normal direction of the layer inclining to the molecular axis. Because the periodic length of the layer (193A) is less than the twice molecular length (220A), it is expained by the normal direction of the layered stripe28.7°tilting to the molecular long axis. With increasing temperature, the angle changes to18.2°. The assembled layered structures of PBLG29-b-PDLG45(ΦPDLG=0.724) and PBLG27-b-PDLG3o (φPDLG=0.653) form based on the PDLG volume fraction (ΦPDLG), therefore, the self-assembly pattern of the diblock copolymer could be regulated by changing the block component.Chapter4describes the syntheses and structural analyses of rod-coil diblock copolypeptide hybrids, polystyrene-b-poly(y-benzyl-L-glutamate)(PS-b-PBLG). We use the same NCA synthesis, and investigate the chemical composition, thermal properties, liquid crystalline nature, and self-assembled thin film strucute of this new synthetic polymer. The two synthesized PS-b-PBLG samples were named as the PS74-b-PBLG152and PS123-b-PBLG292. The volume fraction of PBLG (ΦPBLG) in PS74-b-PBLG152and PS123-b-PBLG292were about0.787and0.811, and the molecular weight distributions are approximately1.4. In DSC analysis, the peaks observed at20℃and80℃corresponds to the glass transition behavior of PBLG and PS segments, and there was no other discovery of phase transition behavior until heating to160℃The unclear liquid crystalline behavior may be caused by long PS segment chains. In soild film system, the PBLG part of rod-like a-helical chain packs in hexagoanl arrangement. Because of the phase separation between PBLG and PS block, the films prepared under magnetic alignment exhibits lamellar periodic structure in nanoscale. The normal normal direction of the layer is similar to PBLG27-b-PDLG3o, which is parallel to the molecular axis direction. By SAXS measurement, we found that the periodic length of the layer is less than the stretch length of a-helix, it is reasonable to speculate the a-helical part may fold in their self-assemblied layer structures.In this study, we synthesize two kinds of polypeptide block copolymer, PBLG-b-PDLG and PS-b-PBLG, and investigate their self-assembled structures in films, respectively. These two compounds combine with the a-helical rigid rod shaped and the self-assembly properties of the diblock polymers, and both of them formed lamellar self-assembled structures. The layered structure will provide more interesting nature from the diblock polypeptide copolymers.