| The Schiff base reaction is a kind of reaction which based on covalent bond buthas dynamic behaviors. It belongs to a category of covalent bonds called "dynamiccovalent bonds", such as imine bond, acyl hydrazone bond, disulfide bond, trithioester bond, etc. This category refers to a reversible reaction which is controlled bychemical equilibrium, namely any chemical bonds which show reversible formationand breaking characters.Compared with ordinary covalent bonds, the dynamic covalent chemistry arereactions based on thermodynamics control, thus it has similar properties as that insupramolecular chemistry,"check" and "correction", in the system. Moreover, thebond energy of dynamic covalent bonds is lower than the ordinary covalent bond, butrelatively stronger than the supramolecular interactions. In this way, this type ofdynamic covalent chemical bonds has stability between supramolecular interactionsand ordinary covalent bonds, but at the same time may be affected by the competitivespecies which influences the reaction equilibrium. So this kind of reaction presentscolorful performances, and has been widely used in many fields such as self-healingmaterials.The construction of hyperbranched polymers which utilizes the Schiff base(including imine bond, acyl hydrazine, etc.) as a linker has many characteristics ofwhich the traditional method lack. And since its dynamic performance, the branchedsystem formed can adjust its structure gradually, finally to achieve the most stablestate in thermodynamics. In addition, the system has abundant stimuli-responseperformances, which is also the highlight in the process of building intelligentmaterials.Utilizing β-cyclodextrin (β-CD) as the core, making use of the high reactingactivity of the6-hydroxyl groups as the binding sites, after react withα-isopropylbromide butyryl bromide or carbon disulfide andα-bromine ethyl butyrate, β-CD coremulti substituted ATRP initiator and RAFT chain transfer agent were obtained. Thestructural information of these products were obtained through Nuclear MagneticResonance Hydrogen Spectrum (1H NMR), Magnetic Resonance Carbon Spectrum(13C NMR) and Matrix-Assisted Laser Desorption/Ionization Time of Flight MassSpectrometry(MALDI-TOF-MS) characterization, and the degree of substitution of each product obtained through two pathways was discussed. N-Isopropylacrylamide(NIPAM) was used as monomer in synthesizing β-CD core star polymersvia ATRP and RAFT polymerization. The comparison between the molecular weightdistribution was based on Gel Permeation Chromatography (GPC) to find methodssuitable for its polymerization.Making use of the the host-guest chemistry of cavity in β-CD, selecting theappropriate guest molecules, such as para-phenylene diformaldehyde, para-phenylenediamine, etc., rotaxane structures with axial reactivity were obtained, then thepsudopolyrotaxanes was synthesized through the Schiff base reaction, which is justpolymer brush. It can solve the insolubility problem of the poly Schiff base.Psudopolyrotaxanes with lower degree of polymerization also has thestimuli-response behavior of Schiff base.Using the Schiff-base reaction between the most common branched polymerpolyethylene imine (PEI) and two dialdehyde, hydrogel system can be obtained easily.Due to the high proton capacity of PEI molecule, the gel can be stable in a broad pHextent. In addition, the alkaline and reductive environment of the system itself is verysuitable for the growth of silver nanoparticles directly on the surface of hydrogel,which can be utilized in antibacterial and other application fields. |
