Study On Synthesis And Properties Of Star Homo- And Block Copolymers Of 4-arm Dimethylaminoethyl Methacrylate

Star polymer is defined as a polymer that consists of multiple linearchains linked together at one end of each chain by a junction point, which exhibits ahigher degree of functionality, a smaller hydrodynamic dimension and lower solutionviscosities compared to analogous linear polymer with similar molecular weights. Witha hydrophilic block and a hydrophobic block, the amphiphilic diblock copolymers canself-assemble to form micelles with various morphologies. This interest is motivated bythe attractive applications of polymeric micelles to various research areas, such asdeflocculation, drug delivery vehicles and nanotechnology. In recent years, to be a hotresearch field, much attention has been paid to the design and synthesis of star polymersand block copolymers as well as their functionalities.It is well known that poly(dimethylaminoethyl methacrylate)(PDMAEMA) canundergo a conformational transition due to hydrophobic or hydrophilic molecular chaininteractions by varying pH value and temperature, which has attracted much attention inrecent years attributed to its variety of applications, such as environmental protection,drug delivery systems, gene delivery systems, etc. So it can be expected to obtain bettermaterials from the star or block polymers of DMAEMA.Based on the above, the recent development of synthesis of star polymers, blockcopolymers and silver nanoparticles were simplely introduced. Considering of thespecial properties of PDMAEMA, the synthesis of four arm star homopolymers(StarPDMAEMA) and block copolymers(Star PMMA-b-PDMAEMA) of DMAEMA wereachieved by atom transfer radical polymerization, and the self-assembly behavior ofStar PMMA-b-PDMAEMA in aqueous solution was studied. Silver nanoparticles werealso prepared successfully by reducing aqueous solutions of AgNO₃ at ambienttemperature with star or line PDMAEMA. The main results obtained in this thesis are asfollows.1. The synthesis of 4-arm dimethylaminoethyl methacrylate star polymer has beenachieved successfully by atom transfer radical polymerization in aqueous acetone atambient temperature using CuX as catalyst, bpy/o-phen as a ligand reagent andpentaerythritol terakis(2-bromoisobutyrate) as the initiator, respectively. The influenceof different reaction conditions on the polymerization, such as catalyst, ligand and water, were studied. The results showed that the polymerization with CuCl/o-phen/PT-Br wasclosely controlled, and that the rate of polymerization was increased in the presence of alittle of water in the reaction system. The star polymer was characterized by FT-IR, ¹HNMR, GPC and UV-Vis spectrum, and the polymerization kinetic and thetemperature-responsive behavior of the star polymer was also studied.2. The synthesis of 4-arm methyl methacrylate star polymer with low polydispersity(Mw/Mn＜1.25) has been achieved successfully by ATRP in aqueous acetone at 35℃,using PT-Br/CuCl/bpy as a catalyst system. GPC results confirmed that PMMA-Br is a4-arm start structural polymer. Then, the star PMMA-b-PDMAEMA was synthesizedvia the macroinitiator method when star PMMA-Br was used as macroinitiator toinitiate the polymerization of DMAEMA. The star block copolymer structure wasconfirmed by FT-IR, ¹H NMR and GPC. Chain aggregation into polymeric micelles inaqueous solutions was observed by ¹H NMR, and the morphologie and size of themicelle was also studied by TEM and DLS.3. Silver nanoparticles were prepared by reducing aqueous solutions of AgNO₃ atambient temperature with star or line PDMAEMA, which acted as both reducing andstabilizing agents for the formation of silver nanoparticles. The product wascharacterized by XRD, FT-IR, TEM and UV-Vis spectrum. The UV-Vis results showedthat star PDMAEMA reacted much more rapidly than line PDMAEMA under the sameconditions. The TEM results revealed that the size of silver nanoparticles could becontrollable by the change of AgNO₃ concentration in aqueous solution.