Amphiphilic Block Copolymers In Aqueous Polar Organic Solvent Mixtures PDF Download

Amphiphilic ionic block copolymers are promising materials for the fabrication of ion-exchange membranes in fuel cells, water purification and advanced molecular engineering applications, such as nanotemplating. For example, block copolymer architectures provide a route to fabricate membranes with tunable transport properties through polymer self assembly. A significant challenge in this field is the synthesis of amphiphilic copolymers, where the intrinsic immiscibility of the hydrophobic and hydrophilic monomers complicates polymerization. To address the immiscibility between sodium p-styrenesulfonate and styrene monomers, styrenesulfonate monomers were neutralized by hydrophobic trialkyl ammonium salts via ion-exchange reactions, and synthesized successfully by RAFT polymerization with low polydispersity (PDI). Diblock or triblock copolymers with well-defined architectures were obtained by sequential RAFT polymerization with styrene. These sulfonate groups were then converted to the sodium salt form via ion-exchange to obtain amphiphilic ionic block copolymers. It was observed that dimethyl n-alkyl ammonium salts of polystyrenesulfonate displayed thermo-reversible gelation behavior in low polarity organic solvents. The investigation of the gelation behavior as a function of temperature, concentration, and solvent was consistent with gelation driven by the ionic aggregation of the polymer as would be expected for polyelectrolyte surfactant complexes in non-polar solvents. Cationic amphiphilic block/graft copolymers containing quaternary ammonium salts were prepared by the RAFT polymerization of polystyrene-b-poly(vinylbenzyl chloride) (PS-b-PVBC) copolymers, and sequential post-polymerization quaternization of the PVBC blocks. PS-b-PVBEA-b-PS triblock copolymers with well-defined architectures were obtained and the ion conductivity of the corresponding membranes, as well as the morphology of the membranes, was investigated. To improve the mechanical properties of the membranes, different architectures, such as pentablock, heptablock and graft copolymers, were designed and synthesized by RAFT polymerization, and chemical crosslinking was employed to improve the mechanical properties and control the swelling in water. Lastly, a new method to prepare multiblock copolymers via a facile route was developed. Polytrithiocarbonates were prepared by condensation polymerization of a dicarboxylic acid functional trithiocarbonate and a diol, and the trithiocarbonate group was controlled by tuning the amount of acid catalyst and reaction time. The polytrithiocarbonate RAFT agents were used to polymerize PS, polystyrene-b-poly (tert-butylstyrene) (PS-b-PtBS), and PS-b-PVBC. The PDI of the polymers toward 2, but the PDI of the polymer blocks between two trithiocarbonate groups was narrow (1.1-1.3 for PS and PS-b-PtBS, and 1.46 for PS-b-PVBC). The PVBC segments were quaternized to achieve anionic amphiphilic multiblock copolymers.