Design, synthesis, and characterization of functional block copolymers containing fluorinated or hydrophilic segments by ATRP
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Well-defined functional block copolymers containing either a fluorinated or a hydrophilic segment can be synthesized via a controlled free-radical technique, known as atom transfer radical polymerization (ATRP). Their self assembly characteristics in the solid state and in solution were examined in this work with the aim of developing ultralow dielectric constant materials and templates for conductive polymer synthesis, respectively. We demonstrated the controlled synthesis via ATRP of block copolymers containing poly(pentafluorostyrene) (PPFS) and a degradable polymer, such as poly(methyl methacrylate) (PMMA), poly([epsilon]-caprolactone) (PCL), or poly(D,L-lactide) (PLA). These block copolymers microphase separate in the solid state to form periodic nanostructures, such as alternating lamellae, a bicontinuous gyroid on a cubic lattice, cylinders on a hexagonal lattice, or spheres on a body-centered-cubic lattice, depending on the volume fraction of each block and the interblock segregation strength. Additionally, we quantified the interblock segregation strength of PPFS/PMMA, demonstrating that this block copolymer is only approximately twice as segregated as its nonfluorinated counterpart poly(styrene-[beta]-methyl methacrylate) due to the symmetric placement of the polar C-F bonds on the benzene ring in PPFS. We also showed that the self-assembly characteristics of PPFS-containing block copolymers can be used to create nanoporous fluorinated films with ultra-low dielectric constants in the range of 1.7 - 1.9. The dielectric constants are tunable through manipulation of the volume fraction of the degradable block in the parent block copolymers. We also demonstrated the controlled synthesis via ATRP of block copolymers containing poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA) with either poly(oligo(ethylene glycol) methyl ether methacrylate) (PEGMA) or poly(methyl acrylate) (PMA). We showed that PEGMA/PAAMPSA formed well-ordered nanostructures in the solid state when cast from strong hydrogen bond accepting solvents, such as DMSO and DMF. PEGMA/PAAMPSA can also be used as the acid dopant in the synthesis of conductive polyaniline (PANI). Additionally, we studied the micelle formation of PMA/PAAMPSA and subsequently used these micelles as templates to create spherical conductive PANI nanoparticles. The size and size distribution of these PANI nanoparticles were dictated by the corresponding characteristics of the micellar template.