Preparation And Properties Of Chiral Microspheres Constructed By Helical Polyacetylenes Containing Schiff Base Functional Groups

Chiral helical structures,as a very important form of chirality,widely exist in nature.They are relatively stable and can provide large space available for storing information.As a large group of unique chiral micro-and nano-scaled polymer materials,helical substituted polyacetylene microspheres have both the optical activity derived from helical polymer chains and the large specific surface area of microspheres.Such chiral microspheres have been widely used in many fields such as chiral recognition,chiral resolution and asymmetric catalysis.It is of great significance to combine the helical main chains of substituted polyacetylene with functional groups in one entity,which can greatly broaden the microspheres' application range and meanwhile can improve their application values.Schiff base is a kind of organic compounds(or functional groups)which contain reversible imine group[-(C=N)-]generated by the reaction between an amino group(-NH2)or hydrazine group(NH2-NH2)with an aldehyde group(-CHO)or a ketone group(-C=O),or between other similar functional groups under certain reaction conditions.Schiff bases and the derivatives have been widely used for developing catalyst intermediates,fluorescent reagents,self-healing polymeric materials,anticorrosive materials and biological sterilizing agents because of the excellent ionic coordination ability and pH-response ability of its characteristic functional group[-(C=N)-].More recently,it was reported that Schiff bases can be utilized as electrode for batteries and be used to prepare organic framework materials.The excellent properties and the extensive applications of Schiff bases have been attracting rapidly growing attention.In this thesis,we introduced Schiff bases'dynamic imine group into the alkyne monomers and prepared optically active helical polyacetylene microspheres in two ways(polymerization of chiral alkyne monomers and chiral induction approach).The chiral helical polyacetylene microspheres containing Schiff base functional groups and loaded with drug(with citronellal as chiral drug model)were prepared by precipitation polymerization and applied to the enantio-differentiating release towards chiral drug.The chiral microspheres constructed by helical polyacetylenes bearing Schiff base functional groups were prepared by suspension polymerization,and polyacetylene microspheres with chiral memory effect were further constructed.Their properties and influential factors were characterized.The main research contents are as follows:1.The chiral substituted alkyne monomer was successfully copolymerized with 4-ethynyl aniline which loaded with chiral citronellal by the Schiff base reaction.The chiral crosslinked polyacetylene microspheres containing chiral aldehyde model drug(citronellal)were successfully prepared by precipitation polymerization.SEM images showed that the microspheres with smooth surface and average size about 1 ?m were successfully synthesized.Circular dichroism(CD)and UV-vis absorption spectra demonstrated that the polymer chains forming the microspheres existed in predominantly one-handed helical structures,which contributed largely to the optical activity of the microspheres.It is worth noting that the release behavior of citronellal could be controlled by regulating the pH of release solution,due to the pH sensitivity of Schiff base structure.The release process was promoted under acidic conditions,but was inhibited under alkaline conditions;in neutral releasing solutions,the chirality of microspheres became the key deciding factor.The chiral release experiments showed that synergistic effects occurred between the chirality of the helical polymer chains in microspheres and the pH-dependent property of Schiff base.2.Chiral Schiff base alkyne monomers were prepared by the reaction of a chiral source molecule(a-phenylethylamine)with 4-ethynylbenzaldehyde,and then we successfully synthesized chiral microspheres composed by helical polyacetylenes containing Schiff base functional groups in side chains by suspension polymerization.The microspheres demonstrated chiral memory feature after removing the chiral a-phenylethylamine moieties,which was achieved by stirring the microspheres in acidic solvent to completely hydrolyze the Schiff base structure and then excluding the chiral?-phenylethylamine via washing.In addition,the effects of the amount of crosslinker and the type of solvent on the optical activity and morphology of the microspheres were studied.A formula with CHC13 as cosolvent,3 mol%crosslinker(3 mol%of the total monomer)and 2 wt%PVA as stabilizer was confirmed to be the optimal formulation for preparing the microspheres.The products were characterized by FT-IR NMR element analysis and XPS techniques.Additionally,SEM images showed that the microspheres were relatively uniform in size and the sizes were 450±80 ?m.Circular dichroism(CD)and UV-vis absorption spectra demonstrated that the polymer chains still existed in predominantly one-handed helical structures even after acid hydrolysis.The results showed that the microspheres after removing the Schiff base moieties have the effect of chiral memory.