Cardo groups

Some diamines carrying very bulky substituents like cardo groups can give colorless polyimides. For example, the bis-9,9-(4-aminophenyl)fluorene (FDA) or brominated and acetylenic FDA derivatives react with 6FDA giving copolymer films62 with low birefringence (low difference between in-plane and out-of-plane refraction index) (Fig. 5.8). A new cardo diamine l,l-bis[4-(4-aminophenoxy)phenyl]cyclododecane (Fig. 5.8) reacts with different aromatic dianhydrides with formation of colorless polyimides.63... 

Table 2.2 Names, abbreviations and chemical structures of diamines containing cardo group...

It can be concluded that polyalicyclic cardo groups such as admantane and norbor-nane-type groups are thermally more stable than alicyclic groups such as cyclodo-decane. 

PEEK polymers are characterized by a high crystallinity which can be reduced by PEEK modified with cardo (Latin meaning loop) group which increase the amorphous degree. Sulfonated cardo-group modified PEEK (sPEEK-WC), as shown in Fig. 6.7, has been proposed for DMFC application [182-184]. A comprehensive review of the use of sPEEK and sPEEK-WC membranes in DMFC has been recently performed by lulianelli and Basile [185]. 

Other polysulfone membranes for DMFC were prepared by sulfonation of commercial polyethersulfone with Cardo group (sPES-C) [473] (Fig. 6.9), by sulfonation of a commercial poysulfone and the use of silica as a filler [474], by "click" cycloaddition of alkyne sulphonate to polysulfone containing azide moieties and crosslinked with 1,7-octadiyne [475], and by polycondensation of 4,4 -difluorodiphenyl sulfone (DFDPS) and l,3-bis(4-fluorobenzoyl)benzene,6,7-dihydroxy-2-naphtha lene sulfonate with bisphenol [476]. Commercial poly(phtalazinone ether sulfone ketone (PPESK) [477], Udel (Solvay) polysulfone [478-480], and Lasuf Lati SPA) polysulfone [481] were sulfonated to prepare membranes for DMFC. Relative selectivity larger than 7 have been obtained with some of these membranes [477,478], as indicated in Fig. 6.37. 

Sulfonated multi-block PAES copolymers containing phenolphthalein anilide as a cardo group have been prepared [95], The hydrophobic precursor oligomer was prepared using 4,4 -dihydroxydiphenyl sulfone and 4,4 -dichlorodiphenyl sulfone. The hydrophilic oligomer was prepared from disodium-3,3 -disulfonate-4,4 -dicldorodiphenyl sulfone. Sulfonic acid group is added by a post-sulfonahon process. 

Figure 4.5 Fluorinated polyamides (PAs) containing different cardo groups [2,5,10,12,13,43],...

A different cardo group like xanthene has been used to improve the solubility of PAs [14], Ma et al. studied the effect of the xanthene group on the polyamide properties. They prepared the diacid chloride of 9,9-( i5[4-(4-chloroformylphenoxy)phenyl]... 

Much of this work has been done in an attempt to understand the principles that govern the relationship between gas permeability and permselectivity with polymer repeat unit structure because of an interest in developing polymeric membranes that exhibit higher permeability and permselectivity simultaneously. The cardo group, bulky pendant groups, kinks, and bends in the polymeric structures inhibit the close packing, which, in turn, increases the FFV and rigidity simultaneously and improves the processability, permeability, and permselectivity. 

Banerjee and group have developed a number of fluorinated PAs for the separation of benzene/cyclohexane by PV [11-13]. Several PAs were prepared from fluorinated bis(ether amine)s with different bulky cardo groups. The backbone of the PAs was systematically altered by changing the acid moiety (terephthalic acid, isophthalic acid, and 5-tert butyl-isophthalic acid), and they studied the effect of these structural changes on the PAs PV properties [72]. The values related to benzene/cyclohexane PV are tabulated in Table 4.9. 

Among other studies, the sulfonation of a new PEEK based polymer, the polyetheretherketone/cardo-group (PEEK-WC), represents at moment a way to obtain a new sulfonated polymer (S-PEEK-WC) showing interesting electrochemical performances and very good thermo-chemical properties with respect to the Nafion. 

As expected, the presence of the isomeric structures has no effect on properties such as glass transition temperature or solubility (d). Both isomers introduce bends into the polymer chain due to a dihedral angle between the phenyl substituent in the 3-position of the indan group and the aromatic ring within the indan system. Also, the indan group can not be viewed as a classic cardo group as introduced by fluorene or phthalein groups. 

DCM, dichloromethane DMA, N,N dimethylacetamide DMF, N,N dimethylformamide NMP, l-methyl-2-pyiTolidone PDMS, polydimethylsiloxane PI, phase inversion PVDF, polyvinylidene fluoride RH, relative humidity SD, spinodal decomposition SE, solvent evaporation SPEES-WC, sulfonated polyetherethersulfone with cardo group SPEEK, Sulfonated polyether ether ketone TBABr, tetrabutilamonium bromide VIPS, vapor-induced PS. 

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