Polyimide blends

There are other high temperature polymers that have also been shown to form miscible mixtures. Polyimides (Pis) have already been discussed in blends with PBI. Other miscible PI blends have been reported with poly (ether-ether ketone) (PEEK), polyethersulone (PES) and sulfonated PEEK. Although the mechanism for miscibility in PBI/PIs was demonstrated to be related to hydrogen bonding between the chains of the two components, the mechanism of miscibility in some of these other blend systems was not as clear. 

In order to better understand the miscibility in polyimide-based systems. Sun et al prepared pairs of polyimide blends with different molecular structures in two ways mixing of the polyamic add precursors with subsequent imidization and direct solution blending of the two polyimides. Dynamic mechanical analysis (DMA) techniques showed that all of the blends prepared in the two different ways are miscible, as evidenced by the existence of only one Tg for all the blends. It was proposed that the miscibility of these polyimide/polyimide blends is a result of the strong inter-molecular charge-transfer interaction between the two chains of the blend components. 

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Of course, this re-equilibration behavior of two homopoly(amic acids) can be eliminated if one of the components does not exhibit this back reaction. Recombination of different fragments is not possible and stable polyimide precursor blends are accessable [119]. For example, combining a relatively flexible poly(amic acid), hexafluoroisopropylidene diphthalic anhydride (6F)/2,2-bis(4-aminophenoxy-4 -phenyl) propane (BDAF), with a rigid poly(amic alkyl ester), PMDA/p-phenylene diamine (PDA), produced microphase separated polyimide blends as can be interred by the persistence of the... 

Table 9 summarizes the calculations for % from seven pairs of polyimide blends ranking them in order of increasing %. From this order, some interesting observations could be made. For example, 6F1M/6F1P had the lowest calculated x, while the polymers with rigid dianhydrides, such as PMDA or BPDA,... 

Table 10 summarizes the glass transition behavior of these polyimide blends and demonstrates that there is only one Tg for each blend. Similar results have been confirmed by Koros of the University of Texas [29], This data confirms that as long as the dianhydride is the same in the composition, the change of 6F diamine from 3,3 to 4,4 does not alter solubility significantly, and the pairs are miscible. The relationship between the Tg and the Fox equation is discussed by MacKnight et al. work [17]. 

Finally, Davis investigated the effects of exposing polyimide blends to... 

The fluorinated copolyimides (including homopolyimides) are all more transparent than the nonfluorinated PMDA/ODA. The color of 10-pm-thick films changes gradually from bright yellow to colorless as the 6FDA/TFDB content increases. All these copolyimide films are also homogeneous compared with polyimide blends of 6FDA/TFDB and PMDA/TFDB. 

Fig. 37. High Tg polyimides blended with a benzhydrol bisnadimide (Fig. 33) [121]...

Watcharaphalakorn, S., Ruangchuay, L., Chotpattananont, D., Sirivat, A. and Schwank, J. (2005) Polyaniline/polyimide blends as gas sensors and electrical conductivity response to CO-N2 mixtures . Poly Inter., 54,1126-33. 

T.-S. Chung and E. Ronald Kafehinski. Miscibility of fluoro-containing polyimide blends. Po/ymer, 37(9) 1635-1640, April 1996. 

X. Kong, F. Teng, H. Tang, L. Dong, and Z. Feng. Miscibility and crystallization behaviour of poly(ether ether ketone)/polyimide blends. Polymer, 37(9) 1751-1755, April 1996. 

J. W. Simmons and 0. M. Ekiner. Polyimide blends for gas separation membranes. US Patent 7 018445, assigned to L Air Liquide, Societe Anonyme a Directoire et Conseil de Surveillance Pour I Etude et TExploitation des Procedes Georges Claude (Paris, FR) N/A (, March 28, 2006. 

Bi H, Wang J, Chen S, Hu Z, Gao Z, Wang L, et al. Preparation and properties of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide blend membranes for fuel cell application. J Membr Sci 2010 350(l-2) 109-16. 

Campbell JA, Goodwin AA, Mercer FW, Reddy V. Studies on a miscible polyimide blend. High Perform Polym 1997 9(3) 263-79. 

G. C. Kapantaidakis, G. H. Koops, High flux polyethersulfone-polyimide blend hollow fiber membranes for gas separation, J. Membr. ScL, 204, 153-171 (2002). 

The phase behavior observed with the PBl/Ultem blends is to be contrasted with the phase separation that was observed in blends of PBI with another polyimide, XU218 from Ciba Geigy (Choe et al. 1991). That system showed phase separation only above 400 °C. The actual phase separation temperamies are determined by the blend composition. Thus, the phase behavior that is observed in PBl/polyimide blends is dependent both on the type of polyimide and the thermal history of the blends. 

Tiptipakom, S., Damrongsakkul, S., Ando, S., Hemvichian, K., Rimdusit, S. Thermal degradation behaviours of polybenzoxazine and silicone polyimide blends. Polym. Degrad. Stab. 92, 1265-1278 (2007)... 

Hybrid membranes have also been demonstrated to be efficient for olefin/paraffin separation Thermally annealed 6-FDA polyimide blends embedded with ZIF-8 nanoparticles showed attractive performances for the C3H5/C3Hg separation [129]. C3H5... 

Rimdusit, S. Benjapan, W. Assabumrungrat, S. Takeichi, T. Yokota, R., Surface Segregation of Siloxane Containing Component in Polysiloxane-Block-Polyimide and s-BPDA/ODA Polyimide Blends. Polym. Eng. Sci. 2007,47, 489-498. 

L. Wang, B.L. Yi, H.M. Zhang, D.M. Xing, Characteristics of polyethersulfone/sulfo-nated polyimide blend membrane for proton exchange membrane fuel cell, J. Phys. Chem. B 112 (14) (2008) 4270 275. 

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