Synthesis, cross-linking and carbonization of co-polyimides containing internal acetylene units for gas separation

Abstract

Cross-linkable polyimides containing internal acetylene units have been synthesized by random copolymerization of 6FDA dianhydride, 2,3,5,6-tetramethyl-1,4-phenylenediamine (Durene) and 4,4 ′ -diaminodiphenylacetylene (p-intA) diamine as materials for gas separation. Compared with 6FDA-Durene polyimide, 6FDA-Durene/p-intA co-polyimide shows denser polymer chain packing, which is confirmed by wide-angle X-ray diffraction (WAXD). The thermally treated co-polyimides are insoluble in various solvents and show an increase in T g , indicating the formation of network structures among the polymer chains. Differential scanning calorimetry (DSC) and FT-Raman suggest that cross-linking arises from Diels-Alder cycloaddition between the internally arranged acetylene units along the polymer main chain, resulting in extended conjugated aromatic structures. The thermally cross-linked membranes show enhanced resistance to CO 2 plasticization up to around 5 × 10 6 Pa (700 psi). The rigidified membrane structure provides increased gas selectivity without severely compromising gas permeability. The gas separation performance of carbonized membranes is remarkably superior to those of neat and cross-linked copolyimides because of a large increase in rigidification in the polymer matrix. A Diels-Alder cycloaddition reaction produces a much more rigid and planar conjugated aromatic structure in the polymer chains and results in a higher degree of graphitization during carbonization, which is confirmed by XPS and WAXD. Carbon membranes derived from co-polyimides with more internal acetylene units show much better gas separation performance than those derived from polyimides without internal acetylene units.

A novel zeolitic imidazolate framework based mixed-matrix membrane for efficient CO 2 separation under wet conditions

“…The temperatures at which testing specimen loses its 5 and 10% weight, denoted by T d5% and T d10% respectively, in TGA analysis determine the thermal stability of a material [56] . Table 1 summarizes some important thermal parameters of the synthesized materials.…”

Natural gas purification and olefin/paraffin separation using cross-linkable dual-layer hollow fiber membranes comprising β-Cyclodextrin

“…The separation performance of 6FDA polyimides generally degrades for separation of highly soluble gases such as CO 2 or hydrocarbons at relatively high pressures. This phenomenon is referred as plasticization [8,17,[23][24]. In the occurrence of plasticization, the gas pair selectivity is diminished and the ideal selectivity measured by means of pure gas tests can no longer be used to estimate the mixed gas membrane performance [25].…”

“…In the occurrence of plasticization, the gas pair selectivity is diminished and the ideal selectivity measured by means of pure gas tests can no longer be used to estimate the mixed gas membrane performance [25]. Crosslinking has been recommended as a way to improve the membrane performance by decreasing plasticization effects and improving the selectivity [23,26].…”

Synthesis, characterization, and CO2 permeation properties of acetylene‐terminated polyimide membranes

“…The crosslinking technique between polymer chains is one of the efficient approaches for suppressing plasticization induced by CO 2 [5]. Many types of reactions have been reported including the monoesterification and transesterification reactions of carboxylic acids [6–8], decarboxylation‐induced crosslink reaction [9], imide ring‐opening reaction [10–12], graft crosslink with etherification reaction [4, 13], ultra violet crosslink [14–16], acetylenes of a Diels‐Alder‐type cycloaddition reaction [17–19], and crosslink using dendrimer [20, 21]. Although previous crosslinking techniques have been available in plasticization, gas permeability largely decreases because of the densification of crosslinked membranes attributed to a higher crosslink density.…”

“…Because this crosslinking reaction requires thermal treatment at over 350°C, more moderate temperature will be needed. For gas separation membranes, the use of the crosslinking approach for polymer blends containing acetylene‐terminated oligomer [17, 26], diacetylene‐containing polyimide [27], and polyimide with internal acetylenes [19] has been reported. These crosslink reactions were prepared by imide oligomer or prepolymer, whereas acetylene‐terminated polymer has not been investigated.…”