A thermal approach to the generation of stable diblock copolymer templates using thin films

Thermally crosslinkable diblock copolymers were studied for their ability to self-assemble and microphase separate, creating polymeric domains on the order of nanometers that could be stabilized with the application of heat. Selective degradation of the uncrosslinked phase afforded a nanoporous template. The stability of these phase-separated structures is crucial for subsequent device fabrication, especially when one of the components is removed to create a nanoporous structure. Nanoporous structures can be used for the fabrication of nanoscopic materials, lithographic templates, and selective filtration on the nanometer size-scale. This dissertation focuses on the synthesis and characterization of novel diblock copolymers and their use in the creation of stable nanoporous templates via thermal crosslinking.; Two methods were used to this end. The first involved the use of benzocyclobutene chemistry to create thermally crosslinkable styrenic polymers, namely poly(styrene- r-vinyl benzocyclobutene) (PSBCB). PSBCB was synthesized via living free radical polymerization using a hydroxy-functionalized alkoyamine initiator. This polymer was used to initiate D,L-lactide via ring-opening polymerization, to create a diblock copolymer with a base degradable poly(lactic acid) (PLA) block. Thin films (∼30 nm) of PSBCB-b-PLA polymer, on a gold-coated substrate, were shown to microphase separate with cylindrical domains of PLA oriented perpendicular to the substrate. Annealing the polymeric thin films, followed by subsequent thermal crosslinking, stabilized the microphase-separated structure. The PLA cylinders were removed using base to afford a nanoporous template. These nanoporous templates were shown to be thermally and solvent stable, unlike their uncrosslinked PS-b-PLA analogs.; The second method to generate thermally stable nanoporous templates, used polystyrene (PS) as the uncrosslinked block and polyacrylonitfle (PAN) as the thermally crosslinkable block. Polystyrene macroinitiator with a bromine end-group (PS-Br) was synthesized using living anionic polymerization techniques. The PAN block was synthesized using atom transfer radical polymerization (ATRP), with the PS-Br as the initiator. These polymers were used to create carbonaceous replicas of the microphase separated structure using a completely thermal process. The PAN block, when heated to 250°C, undergoes stabilization and crosslinking to create a ladder-like polymeric network. Further heating to 600°C under nitrogen, leads to the pyrolysis of the microphase-separated structure, creating nanoporous carbon templates.