Synthesis And Properties Of Amphiphilic Polymers

It is well known that amphiphilic polymers can self-assembly to form a variety of morphologies in selective solvents, on the surfaces of substrates, and in bulk because of phase separation between hydrophilic and lipophilic segments. The unique properties of the amphiphilic polymers lead to many applications in different fields, such as surfactants, nanomaterials, drug carriers, coating materials, adhesives, separation membranes, thermoplastic elastomers. When a fluorinated segment as a hydrophobic part is incorporated into amphiphilic polymers, it can provide some unique properties due to its low surface energy, hydrophobicity, lipophobicity, low refractive index, low dielectric constant, and weathering resistance. Since the properties of polymer depend on its structure, there is no doubt that the morphology of assemblies formed by amphiphilic polymers is related to the length, distribution, and chemistries of each chain segments as well as the polymer architectures. The main content of this dissertation includes design and synthesis of amphiphilic monomers and polymers, investigation on the relationship of structure and properties of polymers and their applications.1. Two kinds of Y-shaped amphiphilic fluorinated monomers,1-(1H,1H,2H, 2H-perfluorodecyloxy)-3-(3,6,9-trioxadecyloxy)-propan-2-yl acrylate (FA) and N-(1H,1H,2H,2H-perfluorodecyl)-N-(3,6,9-trioxadecyl) acrylamide (FAM), have been designed and synthesized. The RAFT homopolymerization of each monomer in bulk has been investigated, and the results showed that both polymerization bear characters of controlled radical polymerization. The molecular weight increases with increasing conversion of monomer, and the molecular weight distributions of PFA is below 1.4. Both of FA and FAM are soluble in water and exhibit excellent surface activity. The critical micelle concentration (CMC) of FA is 0.15 mmol/L and the lowest surface tension of its aqueous solutions is 20.0 mN/m. FAM shows better surface activity than FA as evidenced by smaller CMC and lower surface tension of the aqueous solutions as 0.038 mmol/L and 18.6 6m//m, respectively. The homopolymers of FA and FAM exhibit good thermostability. Both PFA and PFAM are viscous liquid at room temperature, and it is hardly to obtain high quality thin films on glass substrates. PFA is soluble in common organic solvents and shows surface activity. PFAM is hardly soluble in common organic solvents. These results indicate that the chemical structure of the Y-shaped linking part, which links the hydrophilic group, hydrophobic group, and polymerizable group together, has significant influence on the properties of homopolymers. In order to compare with the fluorinated polymer, a nonfluorinated analogue of FAM, N-dodecyl-N-(3,6, 9-trioxadecyl) acrylamide (CAM), has been synthesized. The homopolymer PCAM shows high solubility in apolar solvents and low solubility in strong polar solvents. This result indicates that the properties are quite different between amphiphilic polymers containing fluorocarbon moieties and hydrocarbon moieties.2. A series of block and random copolymers of FA or FAM with 2-(N, N-dimethyl-amino)ethyl methylacrylate (DMAEMA) have been synthesized and the influence of the copolymer structure on their solution and surface properties has been investigated, including the chemical structure, content and distribution of the amphiphilic fluori-nated monomer in copolymers. The surface activity of copolymers in water was examined by surface tension measurements of their aqueous solutions. The results indicate that the fluorine-containing random copolymers can decrease the surface tension of water effectively (y<25 mN/m), and the critical aggregation concentration (CAC) of copolymers decreases with increasing the content of fluorinated monomer. The copolymers containing FAM have lower CAC and surface tension of aqueous solution than the copolymers containing FA, which means the surface activity of the former is better than the latter. In comparison with random copolymers, the block copolymers are less effective for decreasing the surface tension of water. In addition, the aggregation behaviors of the copolymers have been investigated by 1H and 19F NMR. The results show that the fluorocarbon segments in the hydrophobic domain formed by random copolymers have more mobility than that in the hydrophobic domain formed by block copolymers. The surface properties of the copolymer thin films were examined by static contact measurements using water and oil (hexadecane). All the water contact angles of the copolymers show time-dependent behavior, but the oil contact angles do not change over time. This means the surfaces exhibit environ-ment-dependent sitimuli-responsibility. With increasing the content of fluorinated monomers, the hydrophilicity of copolymer thin film surfaces decreases while the oleophobilicity of the surfaces increases. The block copolymers show better hydro-philic and oleophobic properties than the random copolymers. The water and oil contact angles of the block copolymers containing FAM are higher than those con-taining FA, but the values of the random copolymers containing FAM are lower than those containing FA. When the content of FA in block copolymers exceeds 9.1%, the film surface show excellent hydrophilicity and oleophobicity as evidenced by the water contact angle decreases from 48.19°to 27.81°in 30 seconds and the oil contact angle is 70.40°. Based on this result, we examined the anti-fog and oil-repellent pro-perties of the copolymer thin films containing FA. The experiment results show that the block copolymers with 9.1% of FA exhibits simultaneously good anti-fog and oil-repellent properties. Finally, tercopolymers containg FA, DMAEMA, and 2-hydroxy-ethyl methylacrylate (HEMA) have been synthesized and used to construct durable anti-fog and oil-repellent coatings on the glass surfaces by crosslinking reaction. However it was found that the random copolymers don't possess simultaneously anti-fog and self-cleaning properties.3. A novel Y-shaped non-fluorinated amphiphilic monomer, N-dodecyl-N-(3,6,9-trioxadecyl)-4-vinyl-benzylamine (SCT), has been synthesized and copolymerized respectively with N-vinylcarbazole and N-(4-vinylbenzyl)carbazole by RAFT poly-merization. We investigated dispersion of the multi-walled carbon nanotube (MCNT) with the block and random copolymers in different solvents, including DMF, THF, chloroform, toluene, n-hexane and water. The experiment results indicate that the MCNT can be dispersed by the polymer when a solvent is good for the polymer, and the increasing of the SCT content can improve the dispersion efficiency.4. Well-definedε-caprolactone end-capped polystyrenes have been synthesized by ATRP of styrene usingα-bromo-ε-caprolactone as initiator. After removing the end bromine atoms, the ring-opening reactions of s-caprolactone end groups with nucleo-philes yield monoend-biheterofunctional polystyrenes. Then polystyrene containing dimethylamine and hydroxyl groups at one chain end was used as precursor for constructing V-shaped macromonomer. In order to introduce polymerizable groups into the end of polystyrene, acryloyl chloride was reacted with hydroxyl end group. V-shaped ion-bonded amphiphilic macromonomer has been prepared via ionic interaction between sulfonic acid groups in the sulfonic acid end-capped PEG and dimethylamine groups in the a-dimethylamine-a-acrylate polystyrene.