• Polymer(Korea)
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• v.24 no.2
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• pp.194-200
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• 2000

The diffusion coefficients in polyimide/N-methyl-2-pyrrolidone (NMP) systems were proposed using tile Vrentas-Duda's hole free volume theory. Several free volume parameters included in the diffusion coefficients were obtained from the fundamental physical properties of polyimide and NMP and group contribution theory, and the pre-exponential diffusion coefficient, D$_{0}$ was also determined from the dynamic swelling behavior of polyimide in NMP solution. The experimental swelling behavior of polyimide films in NMP was well described by the theoretical one using the proposed diffusion coefficient.t.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.1
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• pp.56-60
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• 2014

The polyimide composite membranes were prepared with polyimide composite solutions including graphenes by using the phase inversion method. The morphologies of these membranes were significantly changed according to the graphene loadings in composite solutions and the solvent systems of the composite solutions. The finger-like macro-voids were formed in the hollow fiber membranes which were prepared in the NMP solvent system with a small amount of ethanol. As increasing the content of the viscous alcohols such as glycerol or 1,3-propanediol in the composite solution, however, the morphologies of the hollow fiber membranes were changed to sponge-like types. In case of flat membranes, the increase of graphene content in polyimide composites causes that their membranes change from the finger-like macro-porous to sponge-like morphologies.

• Macromolecular Research
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• v.15 no.2
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• pp.160-166
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• 2007

Novel multiblock copolymers, based on segmented sulfonated hydrophilic-hydrophobic blocks, were synthesized and investigated for their application as proton exchange membranes. A series of segmented sulfonated poly(arylene ether sulfone)-b-polyimide multiblock copolymers, with various block lengths, were synthesized via the coupling reaction between the terminal amine moieties on the hydrophilic blocks and naphthalene anhydride functionalized hydrophobic blocks. Successful imidization reactions required a mixed solvent system, comprised of NMP and m-cresol, in the presence of catalysts. Proton conductivity measurements revealed that the proton conductivity improved with increasing hydrophilic and hydrophobic block lengths. The morphological structure of the multiblock copolymers was investigated using tapping mode atomic force microscopy (TM-AFM). The AFM images of the copolymers demonstrated well-defined nanophase separated morphologies, with the changes in the block length having a pronounced effect on the phase separated morphologies of the system. The self diffusion coefficient of water, as measured by $^1H$ NMR, provided a better understanding of the transport process. Thus, the block copolymers showed higher values than Nafion, and comparable proton conductivities in liquid water, as well as under partially hydrated conditions at $80^{\circ}C$. The new materials are strong candidates for use in PEM systems.

• Membrane Journal
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• v.8 no.3
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• pp.157-169
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• 1998

The effects of solvents (DMAc, NMP, 1,4-dioxane) and nonsolvents ($H_2O$, Methanol, n-hexane) on the morphology of 6FDA-p-TeMPD polyimide membrane, prepared by the wet phase inversion method, were studied. In the polymer/solvent/nonsolvent ternary system, the binodal curve, the coagulation value and the relative light transmission were measured, and the solubility parameter difference was calculated. The onset state and rate of liquid-liquid alemixing were predicted and the morphology of membrane was analyzed. It is found that the finger-like pores are formed within discontinuous polymer nodules when the binoclal curve is close to the polymer-solvent (P-S) axis, the coagulation value is small, the reduction of light transmission is easy to occur and the order of solubility parameter difference ($\Delta \delta_{i-j}$) is $\Delta \delta_{S-NS} > \Delta \delta_{P-NS} > \Delta \delta_{P-S}$. The dense skin with small nodules and the sponge type sublayer with macrovoid are formed in the case that the binodal curve is distant from the P-S axis, the onset time of liquid-liquid demixing is long and the order of $\Delta \delta_{i-j}$ is $\Delta \delta_{P-NS} >(\Delta \delta_{S-NS} < > \Delta \delta_{P-S})$. The thick layer of fine nodule coagulation and loosely grown sublayer of nodules appear when the binodal curve is distant from the P-S axis, the onset time of liquid-liquid demixing is very long and the order of $\Delta \delta_{i-j}$가 $\Delta \delta_{S-NS} > (\Delta \delta_{P-NS}$\lessgtr$ > (\Delta \delta_{P-NS} < >)\Delta \delta_{P-S}$ ).