Browsing by Subject "Polyimides"
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Item Improving polyimide membrane resistance to carbon dioxide plasticization in natural gas separations(2002) Wind, John David; Paul, Donald R.; Koros, William J.Polyimide membranes have been widely applied for gas separations due to their attractive permeability, selectivity, and processing characteristics. Their use for natural gas and hydrocarbon separations is limited by plasticization-induced selectivity losses in feeds with significant partial pressures of CO2 and C3+ hydrocarbons. This project focuses on understanding CO2-induced plasticization of polyimide membranes and how it can be controlled by thermal annealing and crosslinking. Covalent and ionic crosslinking are investigated as approaches for suppressing plasticization, while retaining attractive transport properties. A novel covalent crosslinking protocol has been developed, which offers significant advantages over the traditional post-treatment that was initially used. The twostep crosslinking treatment allows for spectroscopic characterization of the reaction yields in the monoesterification and transesterification reactions. These crosslinking reactions occur at temperatures well below the glass transition and no additives are required in the casting solution, making the approach attractive for the eventual production of asymmetric hollow fibers. The ionically crosslinked membranes are not as stable against CO2 plasticization as the covalently crosslinked materials. By varying the ionic crosslinking density, the effects on long-term sorption and permeation at high CO2 pressures were investigated. From STEM images, it does not appear that heterogeneity in the ion distribution is the cause of the membrane plasticization. With covalent crosslinking, the copolymer composition, crosslinking agent, and thermal treatment are important factors in determining the final membrane transport properties. The crosslinking reaction is accompanied by a heat treatment that can also lead to stabilization of aromatic polyimides. These effects were decoupled by systematic variations in the polymer structure and thermal treatment. In a plasticized membrane, the sorption, diffusion, and swelling processes are all interdependent. The key to controlling plasticization is to control the membrane swelling, since this is related to the increase in polymer chain segmental mobility facilitated by the CO2 sorption. Mixed gas separations demonstrate the non-ideal factors that must be accounted for when modeling membrane performance over a wide range of pressures. The separation performance at practically relevant feed conditions is intrinsically better and more stable than the commercial polymeric membranes currently used for natural gas separations.Item Investigation of polymer waveguides for fully embedded board-level optoelectronic interconnects(2004) Liu, Yujie; Chen, Ray T.Item Synthesis of novel polyimides for the testing of structure-processing and property relations when used to form high temperature polymer matrices(Texas A&M University, 2007-04-25) Tschen Molina, FranciscoHigh-performance polymers have found an extreme range of applications in the aerospace industry. Composites which have polymers incorporated in them can usually meet the needs of the design, and are the ideal materials for aerospace applications due to their light weight, high strength, and radar transparency. Phenyl-ethynyl terminated oligomers, for example, have found many uses in the aerospace industry. Phenyl-ethynyl terminated oligomers (AFR-PEPA-N) exhibit glass-transition temperatures of up to 450????C. Unfortunately crystals form due to interactions of the oligomers. These crystals do not melt until 360????C after 15 minutes when the resin is already 50% cured. Investigation was performed to find any possible alteration to the end-caps and monomer chain elements of the current AFR-PEPA-N. Several siloxane related amines were added to the AFR-PEPA-N chain to form protective coatings when in service at high temperatures. The new poly(siloxane imide) showed an increase in processability while mantaining AFR-PEPA-N properties. In addition, phenyl-ethnyl end-caps were substituted with an ethynyl end-caps which showed no improvement in processability.