Benzene polyimides prepared with

Percentage yields and decomposition temperatures for a series of polyimides prepared from three bismaleimides and four alkylbenzenes are given in Table 2, together with the same data for the corresponding polyimides prepared from benzene. 

In 1988 Heinze and Burton reported a facile synthesis of various a,p,P-trifluorostyrenes.15 These trifluorostyrene compounds were reported to be unstable to cyclodimerization at room temperature when stored neat, especially the compounds that were /lura-substituted with electron-donating substituents. They described the preparation of one compound, l,4-bis(trifluorovinyl)benzene with the observation that the material gelled when allowed to stand neat overnight. They offered the explanation that the gel was a polymer network connected with flnorinated cyclobutanes. Burton later went on to utilize this dimerization reaction for the cross-linking of polyimide thermoplastics.16... 

The key to acetylene terminated polyimides is the availability of the end-capper which carries the acetylene group. Hergenrother (130) published a series of ATI resins based on 4-ethynylphthalic anhydride as endcapping agent. This approach first requires the synthesis of an amine-terminated amide acid prepolymer, by reacting 1 mole of tetracarboxylic dianhydride with 2 moles of diamine, which subsequently is endcapped with 4-ethynylphthalic anhydride. The imide oligomer is finally obtained via chemical cyclodehydration. The properties of the ATI resin prepared via this route are not too different from those prepared from 3-ethynylaniline as an endcapper. When l,3-bis(3-aminophenox)benzene was used as diamine, the prepolymer is completely soluble in DMAc or NMP at room temperature, whereas 4,4 -methylene dianiline and 4,4 -oxydianiline based ATIs were only partially soluble. The chemical structure of ATIs based on 4-ethynylphthalic anhydride endcapper is shown in Fig. 45. 

Oxidative homocoupling of aromatic and heteroaromatic rings proceeds with Pd(OAc)2 in AcOH. Biphenyl (165) is prepared by the oxidative coupling of benzene [104,105], The reaction is accelerated by the addition of perchloric acid. Biphenyl-tetracarboxylic acid (169), used for polyimide synthesis, is produced from dimethyl phthalate (168) commercially [106], Intramolecular coupling of the indole rings 170 is useful for the synthesis of staurosporine aglycone 171 [107]. 

To increase the sorption component of the separation factor, homogeneously distributed tetracyanoethylene, a strong electron acceptor having high affinity for electron donors, was added to the polyimide matrix [77]. It can be seen from data presented in Table 9.12 that this is accompanied by an increase in the sorption component /3s (benzene/cyclohexane) by a factor of 1.5 probably as a result of selective sorption of aromatic compounds by tetracyanoethylene with a simultaneous increase in the diffusion component /3d. The prepared membranes showed good pervaporation properties with respect to benzene/cyclohexane, toluene/isooctane mixtures. For example, for a two-component 50/50 wt% benzene/cyclohexane mixture at 343 K, the flux was 2 = 0.44 kg p,m/m h, and /3p (benzene/cyclohexane) = 48 and for a two-component toluene/isooctane mixture, 45/55 wt%, at 343 K the flux was 2 = 1-1 kg p-m/m h, and /3p (toluene/wo-octane) = 330. 

Separation of aromatic/aliphatic mixtures by pervaporation using the PBO membranes was studied by Ribeiro et al. The PBOs were prepared by the TR of ort/jo-fimctionalized fluorinated polyimide films (Figure 5.60). They used different feed streams, such as toluene/ -heptane or benzene/ -heptane mixtures. All the PBOs were selective toward the aromatic hydrocarbon. The PBO membranes showed higher selectivity (a=6.7, at 80 °C) and 25 times higher permeability (toluene, 220 Barrer, at 80 °C) in comparison to their precursor polyimides (toluene, 8.9 Barrer and a =1.9, at 80 °C). These increases in hydrocarbon permeability for the fluorinated PBO membranes are due to their larger hydrocarbon uptake and lower packing efficiency of the polymer chains, that is, increase in FFV in comparison to their precursor polyimides [91]. In all cases for a given diamine, the replacement of the >C(CF3)2 unit in the dianhydride (i.e., with the replacement of the fluorinated dianhydride with a non-fluoiinated one) resulted in an approximate 10 times reduction in hydrocarbon permeability, and consequently a reduction in total flux, with an increase in selectivity. 

Baneijee et al. [107] prepared polyimide-POSS (PI-POSS) nanocomposite membranes applying thermal imidization. At first, poly(amic acid)s were generated by the reaction of several diamine monomers, namely 4,4-( w[3 -trifluoromethyl-4 (4 -aminobenzo xy)benzyl]biphenyl l,4- w[3 -trifluoromethyl-4 (4 -aminobenzoxy)benzyl]benzene 2,6-te[3 -trifluorom ethyl-4 (4 -aminobenzoxy)benzyl]pyridine and 2,5 - w[3 -trifluoromethyl-4 (4 -aminobenzoxy)benzyl] thiophene with 6FDA as the dianhydride and 2 wt% POSS-NH2 as the nanofiller. The structure of poly(amic acid) intermediate, which was thermally imidized to form polyimide chain end tethered POSS, is shown in Scheme 6.25. 

Moore and MitchelH prepared soluble poly(enaminoester) (X) from a.a -bis(carbomethoxy) diacetyl benzene and aromatic diamines. The polymers were subsequently thermally cyclized (Conrad-Limpach reaction) to poly(quinolines) (XI), which is analogous to the conversion of poly(amic acids) to polyimides in terms of converting a soluble prepolymer to a stable polymer of cyclized, rigid ring structures with the formation of volatile by-products. The cyclized product however, was infusible and insoluble. 

Figure 9.9 Synthesis of fluorinated polyimides marketed by DuPont. NR 150 A2 is poiyimide 8 prepared from 4,4 -[2,2,2-trifiuoro(1-trifiuoromethyi) ethyiidene]bis(1,2-benzene-dicarboxyiic acid) dianhydride (6FDA) 5 and ODA 2. NR 150 B2 jg a copoiyimide synthesized by reacting dianhydride 5 with diamines 2, 6, and 7. The macromoiecuie is formed of randomiy distributed repeating units 8, 9, and 10. NR 056X is a copoiyimide comprising recurring units 10 (75%) and 8 (25%).

Abstract Three series of new polyimides were prepared by condensation of imidazole-blocked 2,5-bis(n-alkoxymethyl)-1,4-benzene diisocyanates with pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BPDA), and naphthalene tetracarboxylic dianhydride (NTDA), respectively. After the polymers obtained were spectroscopically characterized, their solubilities, thermal properties and crystalline structures were measured and discussed. It was found that structures and properties of the polyimides having regularly substituted n-alkoxymethyKn-CHjOC Hj j, m=4,6,8) side branches are governed not only by side chain length, but also by main chain rigidity. 

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