Functional Nanoporous Polymers from Block Copolymer Precursors

Abstract Self-assembly of block copolymers provides well-defined morphologies with characteristic length scales in the nanometer range. Nanoporous polymers prepared by selective removal of one block from self-assembled block copolymers offer great technological promise due to their many potential applications as, e.g., membranes for separation and purification, templates for nanostructured materials, sensors, substrates for catalysis, low dielectric constant materials, photonic materials, and depots for controlled drug delivery. The development of nanoporous polymers with well controlled pore wall functionalities remains a great challenge due to the limitation of available polymer synthesis and the nanoscale confinement of the porous cavities. The main topic of this thesis is to develop methods for fabrication of functional nanoporous polymers from block copolymer precursors. A method has been developed, where living anionic polymerization and atom transfer radical polymerization (ATRP) are combined to synthesize a polydimethylsiloxane-b-poly(tert-butyl acrylate)-b-polystyrene (PDMS-b-PtBA-b-PS) triblock copolymer precursor. By using either anhydrous hydrogen fluoride or trifluoroacetic acid, PtBA block can be hydrolyzed to hydrophilic poly(acrylic acid) (PAA) and PDMS can be quantitatively etched. The resultant material is nanoporous PS with hydrophlilic PAA pores. Surface-initiated ATRP and click chemistry have been utilized as ‘grafting from’ and ‘grafting to’ techniques respectively to fabricate functional nanoporous polymers based on nanoporous 1,2- polybuatdiene 1,2-PB, which is derived from a 1,2-PB-b-PDMS diblock copolymer precursor. As a result, nanoporous 1,2-PB with pores decorated of polyacrylates, sulfonated polymers and poly(ethylene glycol) are created. A method of vapor phase deposition has also been generated to obtain nanoporous polymers with functional coatings on pore walls. Vapor phase polymerization of pyrrole is performed to incorporate an ultra thin film of polypyrrole into nanoporous 1,2-PB. The preliminary test shows that nanoporous 1,2-PB gains conductivity. Generally cross-linking is needed to provide sufficient mechanical stability for the matrix which has glass transition temperature lower than room temperature. Insufficient cross-linking can lead to collapse of pores after removal of the sacrificial component. However, with a low cross-linking degree, such collapsed matrixes may have reversible nanoporosity. A collapsed 1,2-PB matrix is prepared by cross-linking insufficiently before etching PDMS block away from a 1,2-PB-b-PDMS diblock copolymer precursor. Nanoporosity with ordered morphology is found to be re-established when the 1,2-PB matrix is subjected to a good solvent. Load and release of macromolecular chemicals in these ‘latently porous’ materials was demonstrated, which is of direct relevance for drug delivery applications.