The Study On Preparation And Characteristics Of Polymer Vesicles Containing Chiral Structure

In this work,a series of amphiphilic block copolymers have been synthesized successfully.On this basis,the structure of vesicles self-assembled from the three copolymers was researched by Polarization Laser-trapping Raman Spectroscopy(PLTRS),then the orientation of azopyridine units has been detected.Afterwards,amphiphilic block copolymers containing chiral functional groups was successfully synthesized,and the new copolymers could generate vesicular morphology through self-assembling.Then enantioselective assembly of copolymers and racemic chiral small molecules was observed during preparation of micro-scale polymer vesicles.In addition,it is also found the supramolecular chirality of the copolymer films coated by vesicle's solution and their enantioselective adsorption ability.Main contents and details of this work are described as following:1.Vesicles with hydrophobic shells have been self-assembled through three kinds of amphiphilic block copolymers containing pendent azopyridine groups with different spacers,namely PNIPAM-b-PAzPyn(n=0,2,6),respectively.By polarization laser-trapping Raman spectroscopy,the photoinduced orientation behaviors of azopyridine groups within the vesicle shells have been investigated and it is found that spacer lengths affect the orientation of the azopyridine groups and the morphologic structure of the vesicle shells.The exact experimental results show that the orientation is dynamic for the pendent azopyridine groups with connecting spacers of 2 or 6 methylene units rather than those without spacers,so the vesicles of PNIPAM-b-PAzPy6 can be changed to show a typical "soft"character compared with its solid films when irradiated with a relatively weak polarized UV light of 190 ?W/cm2.However,the vesicles of PNIPAM-b-PAzPy0 without spacers do not change even though the azopyridine units can be oriented.By quantitative Raman spectral analysis,it is found that the isomerization degree of azopyridine units is 70%for PNIPAM-b-PAzPy6 yet it is 10%for PNIPAM-b-PAzPy0,which shows a close relationship between aggregation and isomerization of azopyridine units under a weak UV light.2.Enantioselective assembly is observed during preparation of vesicles from a solution mixture of an amphipathic block copolymer bearing pendent chiral L-or D-phenylalanine groups in hydrophobic segments and racemic chiral small molecules.Primary experimental results reveal that racemic chiral small molecules have been enantioselectively encapsulated into the hydrophobic shells of assembled vesicles with homochiral bilayer membrane structure,showing reverse CD signals compared with the original vesicles.A further study shows that the enantiomeric excess obtained through the enantioselective assembly is directly dependent on the molecular weight of the hydrophobic chiral chain segments,implying both the hydrophobic interaction and chirality are key points during the assembly of vesicles.Other factors,such as hydrogen-bonding interactions and?-? stacking interaction,are also found to be responsible for the enantioselective assembly phenomenon during the formation of the vesicles.3.Supramolecular chirality is achieved in amphiphilic block copolymer films made through two-step fabrication:self-assembling first and then solution coating.The amphiphilic block copolymer is composed of poly(N-isopropyl acrylamide)(PNIPAM)as hydrophilic segments and poly(methyl methacrylate)with chiral side groups as hydrophobic segments.The films fabricated by twosteps show sensible circular dichroism(CD)signals around a wavelength of 200 nm.However,the new CD signals cannot be detected from films made by directly coating the solution of copolymers on the quartz surface.The CD signal at about 200 nm is from supramolecular arrangement of benzene units connected to the chiral group in the hydrophobic segment.This result is thought to be originated from the aggregation of the copolymer during the first step of the film forming process,and the corresponding investigation into factors affecting this process has been performed in this work.It is also found that the films fabricated by two steps can adsorb chiral small molecules enantioselectively,while the films obtained by coating the solution of copolymers directly have no such enatioselective adsorption ability.