Synthesis Of Amphiphilic Copolymers Of Styrene And (Meth) Acrylates By Atom Transfer Radical Polymerization And Their Self-Assembly In Selective Solvents

In this thesis, well-defined polystyrene (PS) was synthesized via atom transfer radical polymerization (ATRP) using p-α,α'-dichloroxylene (DCX) as initiator. Using the obtained PS as macroinitiator, a series of ABA triblock copolymers of Poly (methyl acrylate)-polystyrene-poly (methyl acrylate) (PMA-b-PS-b-PMA) with different molecular weights were prepared via ATRP as well. Excess 40% potassium hydrate solution was added into the triblock copolymers PMA-b-PS-b-PMA solution in THF. After being refluxed at 75℃ for 48 hours, a large amount of methanol was added to the hydrolyzed solution to precipitate the power of amphiphilic triblock copolymers PKAA-b-PS-b-PKAA . Alternatively, the above mentioned well-defined PS was chloromethylated in chloroform to obtain PS-CH₂Cl. (2-(Dimethylamino)ethyl methacrylate was polymerized using PS-CH₂Cl as macroinitiator and CuCl/ 2,2 ' -Bipyridyl as catalyst in toluene to acquire amphiphilic brush-type copolymers of PS-g-PDMAEMA. The self-assembly behavior of these two types amphiphilic copolymers in different selective solvents was studied by high performance particle sizer (HPPS), TEM, and SEM. The influence of varied factors such as the composition of copolymers, solvents, additive, temperature on the size , stability, and morphology of micelle was investigated respectively.The results show that : the Z-average sizes of micelles that were prepared by amphiphilic copolymers of PKAA-b-PS-b-PKAA in different selective solvents increases with the increasing of molecular weights. The formed micelles are more stable in organicsolvents than in water. The length of PS block exert larger influence on the Z-average size of micelles in organic solvent than in water. When a drop of ethylenediamine was added to benzene solution, the Z-average sizes of the micelles increases almost linearly, and the micelle stability is improved as well. As for brush-type copolymers of PS-g-PDMAEMA, the size of micelle in selective solvents depends on the degree of polymerization of the PDMAEMA. The Z-average sizes of the micelles in deionized water increases with the increase of molecular weights of PDMAEMA while the length of St keeps constant. However, the Z-average sizes of the micelles almost keep constant in the mixed solvent of deionized water and acetone (v/v = 2/3), The Z-average sizes of the micelles prepared by PS-g-PDMAEMA copolymer in deionized water are larger than those in the mixed solvent of deionized water and acetone (v/v = 2/3). The morphologies of micelles being prepared in water/acetone (v/v - 2/3) mixture at different temperatures (from room temperature up to 200 °C) is studied under SEM and the transformation of the morphologies of micelles, from needle-like to microcubic and then to flower-like shape, is observed.