Study On Preparation And Properties Of Environmentally Responsive Copolymers

The living polymerization can be divided into living anionic polymerization, living cationicpolymerization and living free radical polymerization by different initiation modes. Livingfree radical polymerization has been extensively studied in recent years due to the mildreaction conditions and the widely applicable monomer. Living free radical polymerizationcontains initiator-transfer agent-terminator （iniferter）, nitroxide mediated polymerization（NMP） or stable free radical polymerization （SFRP）, and reversible addition fragmentationchain transfer （RAFT） radical polymerization and atom transfer radical polymerization（ATRP）. ATRP is widely available for the polymerization of many vinyl monomers due to thehigh reaction rate, the mild reaction temperature, a wide range of applicable monomers, andused to prepare the determinate structure of homopolymers, block/graft copolymer andorganic/inorganic hybrid materials.The morphology of amphiphilic copolymer assembly is influenced by many factors: suchas the chemical structure, molecular weight, the relative content of the segment, the sequenceof the segment and the nature of the solvent, etc. Due to the novel structure and uniqueproperties of the assembly, it is expected to have broad application prospects in medicine,green materials, bio-engineering, nano-materials, and medical diagnosis.Accordingly, this paper is mainly about the synthesis of different structure copolymers byATRP, the copolymerization reaction and the micellization behavior; the main contentsinclude the following aspects:1. The controlled number-average molecular weight and narrow distributionpoly（4-vinylpyridine） macromonomer （St-P4VP） with a styryl end group was synthesizedby ATRP of4-vinylpyridine using p-（chloromethyl）styrene （CMSt） as functional initiator.Poly（4-vinylpyridine） grafted polystyrene microspheres （P4VP-g-PSt） were then preparedby dispersion copolymerization of styrene with St-P4VP macromonomers. The effects ofpolymerization reaction parameters such as medium polarity, concentration of St-P4VPmacromonomer and polymerization temperature on the sizes and size distribution ofP4VP-g-PSt microspheres were investigated. P4VP distributed on the surface ofP4VP-g-PSt microspheres which made the microspheres had pH responsive.Ag/P4VP-g-PSt composite microspheres were synthesis by Ag nanoparticles stabilized onthe surface of the P4VP-g-PSt microspheres via the in situ reduction of Ag+, thecoordination interaction took place between the Ag+and pyridine group of P4VP. Thecatalytic performance and antibacterial property on Escherichia coli and Staphylococcusalbus of Ag/P4VP-g-PSt composite microspheres was studied.2. The controlled number-average molecular weight and narrow distribution star polystyrene,（PSt-Br）4, was firstly synthesized by ATRP of styrene （St） using pentaerythritol terakis（2-bromoisobutyrate）（4Bri-Bu） as four-armed initiator. Then,（PSt-b-PNIPAM）4wereprepared using （PSt-Br）4as macroinitiator. The self-assembly behaviors of theamphiphilic four-armed block copolymers （PSt-b-PNIPAM）4in mixed solution and thelower critical solution temperature （LCST） of the resulting micelles were investigated. The gold nanoparticles （Au NPs） were immobilized on the surfaces of the micelles by thereduction of the corresponding ions. The micelle-supported gold nanoparticles（Au-micelles） were applied to catalyze the reduction of p-nitrophenol. Moreover, theactivity of the Au-micelle catalyst could be modulated by the temperature and theAu-micelles could be easily recovered by changing the temperature and recycled fourtimes with high catalytic activity.3. The controlled the number-average molecular weight and narrow distributionpoly（4-vinylpyridine） with a chlorine end group （P4VP-Cl） was prepared by ATRP. Then,poly（4-vinylpyridine）-b-poly（tert-butylmethacrylate）（P4VP-b-PtBMA）, was synthesizedusing P4VP-Cl as macroinitiator by ATRP. Poly（4-vinylpyridine）-b-poly（methacrylic acid）（P4VP-b-PMAA） was obtained by hydrolyzing the P4VP-b-PtBMA copolymer underroom temperature. The self-assembly behavior of P4VP-b-PMAA copolymer was alsoinvestigated, the nanomicelles with PMAA core and P4VP corona were formed at low（acidic） pH, while nanomicelles with P4VP core and PMAA corona were formed at high（basic） pH. The morphology of P4VP-b-PMAA micelles was significantly affected bysolvent, segment ratio and pH.4. Macroinitiators poly（2-（dimethylamino）ethyl methacrylate）（PDMAEMA） weresynthesized by ATRP using ethyl-2-chloropropionate （ECP） as initiator. Then amphiphilicblock copolymers PDMAEMA-b-PSt with different segment ratio were synthesized byATRP using PDMAEMA-Cl as macroinitiator. The amphiphilic block copolymersPDMAEMA-b-PSt in selective solution could self-assemble to form micelles. pH,segment ratio and temperature which affected the diameter of the micelles wereinvestigated, the diameter and Zeta value increased with the increment of the hydrophobicchain length or the decrement of pH, and the diameter decreased with the increment of thetemperature. The micelles had pH and temperature dual responsive. The morphology ofmicelle PDMAEMA₁₅-b-PSt₃₄₃was observed by TEM, PDMAEMA-b-PSt self-assembledspherical, bowl, vesicles and beaded micelles, under different pH in DMF.PDMAEMA15-b-PSt343formed macrocomposite micelles in1,4-dioxane/H2O （v/v=94/6）mixed solvent.