Synthesis Of Amphiphilic Block Copolymer By ATRP And Its Self-assembling Behavior In Nonpolarity Solvent

The amphiphilic block copolymers have stronger assembly ability of forming molecular order system, because of the hydrophilic/hydrophobic nature and micro-phase separation character of their molecular chains. In liquid media and under different conditions, amphiphilic block copolymers can self-assemble to form aggregates or micelles with core / corona structure, nano-size and various morphologies. The aggregates have wide applications in many scientific and technical fields, such as biological simulation (vesicle), drugs-delivery system, synthesis of functional nanoparticles, and so on. Atom transfer radical polymerization (ATRP) is one of the significant developments of polymer synthesis chemistry recently. The well-defined polymers with controlled molecular weights and narrow Macromolecules Weight Distribution (MWD) can be synthesized by ATRP in convenient codition, due to its versatility of monomers, simplicity in practice and its versatility of polymerization mode. In this paper, The polymer of PSt-Br with a low polydispersity which end-group is bromide atom have been synthesized by ATRP at 110℃ using 1-phenylethyl bromide (1-PEBr) as initiator, cuprous bromide as catalyst, 2,2′-bipyridine (bpy) as ligand and xylene as solvent. The polymer was characterized by FTIR and GPC. Kinetic study indicated the the polymerization had the characteristics of living polymerization, and followd ATRP mechanism. The polymerization of butyl acrylate (BA) was initiated by macroinitiator PS-Br, resulted in the block copolymer PSt-b-PBA with a low polydispersity, and the length of PBA block is controlled. Then the Amphiphilic block copolymer of PSt-b-PAA has been prepared by hydrolyzing of PSt-b-PBA. The block copolymers of PSt-b-PBA and PSt-b-PAA were characterized by FTIR, GPC and 1H-NMR. The reverse micelle solution of PSt-b-PAA in toluene was prepared by using single-solvent dissolving method. The reverse micellization behavior of PSt-b-PAA in toluene was investigated mainly by fluorescent probe technique using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe, and the influence of concentration of PSt-b-PAA , chain structure and temperature on the reverse micellization behavior of PSt-b-PAA in toluene were investigated. At the same time, the morphologyies of reverse micelles were investigated by TEM observation mean. It was found that NEAH as a polar fluorescence compound can clearly reveal the reverse micellization behavior of PSt-b-PAA in toluene, and can well display the critical micellar concentration (cmc). The experiment results showed that the reverse micelles which have hydrophilic core and hydrophobic shell can formed by spontaneously self-assembling of PSt-b-PAA in toluene. The reverse micelles have the morphology of sphere with diameter ranging from 10 to 20nm, and the small micelles would be join to form much more big spindle aggregates with the increase of the concentration of PSt-b-PAA. The self-assembling behavior of PSt-b-PAA depends apparently on the microstructure of the macromolecules and the temperature. Under the same length of hydrophobic block PSt, the copolymer with longer hydrophilic block PAA has lower critical micelle concentration, and at higher temperature, the copolymer has lower critical micelle concentration.