Browsing by Subject "Polyimides"

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Fundamental gas transport in thermally cross-linked diaminophenylindane (DAPI) containing polyimides
(2018-12) Dose, Michelle Elizabeth; Freeman, B. D. (Benny D.); Paul, Donald R.; Riffle, Judy; Lynd, Nathaniel; Sanchez, Isaac
The trust of this work is to critically examine the chemical and morphological structure of thermally cross-linked polyimides and to identify the effect cross-linking has on fundamental gas transport and plasticization resistance of these materials. To accomplish this goal, a polyimide containing diaminophenylindane (DAPI), hexafluoroisopropylindene (6FDA), and diaminobenzoic acid (DABA), referred to as 6FDA-DAPI/DABA, was synthesized and characterized. The thermal cross-linking process was found to occur by thermal decarboxylation of the carboxylic acid groups contained in DABA. Additionally, upon cross-linking, gas permeability was found to increase with increased cross-linking due to an apparent increase in polymer chain spacing. While thermal cross-linking showed improved plasticization resistance to pure CO₂, C₂H₄, and C₂H₆, mixed gas permeation experiments revealed linear 6FDA-DAPI/DABA was more resistant to plasticization than its cross-linked analog. By studying sorption induced dilation, we concluded that linear 6FDA-DAPI/DABA more readily excluded C₂H₆ from the free volume elements, compared to cross-linked 6FDA-DAPI/DABA, correlating well with the minimal plasticization effects observed in the mixed gas experiments. Additionally, the dilation and sorption data were used to estimate the accessible free volume in the polymer-penetrant mixture. While correlating the diffusion coefficients of CO₂, C₂H₄, and C₂H₆ with the penetrant weight fraction showed anomalous behavior, the relative increase in diffusion coefficients with accessible fractional free volume accurately reflected the plasticization behavior observed in mixed gas permeation experiments. Additionally, this dissertation investigated the fundamental transport of gases in thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIM) to gain an understanding of why these materials tend to perform at or beyond the Robeson Upper Bound for select gas pairs.
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.
Investigation of polymer waveguides for fully embedded board-level optoelectronic interconnects
(2004) Liu, Yujie; Chen, Ray T.
We proposed a fully embedded board-level optoelectronic interconnect structure utilizing polymer waveguides and 45-degree micro mirror light couplers. This structure is expected to provide high-speed, large bandwidth, low power dissipation, as well as compatibility to conventional PCB fabrication process, ease of optical alignment and packaging. High performance polymer waveguide with 45 degree micro mirror coupler is one key component to enable all these advantages. The performance analyses indicate that the polymer waveguide can provide low loss link for optical data and high channel density can be achieved without inducing significant crosstalk. Waveguide intersections and bends can be employed in the waveguide circuitry design to improve the design flexibility and interconnection density. 45 degree mirror couplers can provide high input and output surface-normal coupling efficiency. The fully embedded system features high tolerance to the linear and angular misalignments due to the possible fabrication imperfection. Ultradel 9000 series polyimides are used to form the waveguide and mirror couplers. Fabrication techniques are developed and discussed in detail. Waveguide array and mirror couplers with good quality have been fabricated and characterized. Preliminary integration of polymer waveguide array with MSM photodetector array through 45-degree micro mirror couplers is demonstrated and shows an aggregate bandwidth of 32GHz for a 1×12 channel array. Further integration is under development. An optoelectronic interconnect layer (OIL) will be developed and laminated with the other layers of PCB to improve system performance without inducing manufacturing difficulties.