Aramids solubility

Properties. As prepared, the polymer is not soluble in any known solvents below 200°C and has limited solubiUty in selected aromatics, halogenated aromatics, and heterocycHc Hquids above this temperature. The properties of Ryton staple fibers are in the range of most textile fibers and not in the range of the high tenacity or high modulus fibers such as the aramids. The density of the fiber is 1.37 g/cm which is about the same as polyester. However, its melting temperature of 285°C is intermediate between most common melt spun fibers (230—260°C) and Vectran thermotropic fiber (330°C). PPS fibers have a 7 of 83°C and a crystallinity of about 60%. 

The aramids are formed in the low temperature reaction, -10 to 60°C, of equimolar amounts of the diacid chloride and the diamine in an amide solvent, typically dimethyl acetamide (DMAc) or IV-methji-2-pyrroUdinone (NMP) and usually with a small amount of an alkali or alkaline-earth hydroxide and a metal salt, such as LiOH [1310-65-2], LiCl, Ca(OH)2 [1305-62-0], or CaCl2 added to increase the solubility of the polymer and neutralize the hydrochloric acid generated in the reaction. 

Reichert and Mathias prepared related branched aramids, to those of Kim,t5-34] from 3,5-dibromoaniline (23) under Pd-catalyzed carbonylation conditions (Scheme 6.7). These brominated hyperbranched materials (24) were insoluble in solvents such as DMF, DMAc, and NMP, in contrast to the polyamine and polycarboxylic acid terminated polymers that Kim synthesized, which were soluble. This supports the observation that surface functionality plays a major role in determining the physical properties of hyperbranched and dendritic macromolecules J4,36 A high degree of cross-linking could also significantly effect solubility. When a four-directional core was incorporated into the polymerization via tetrakis(4-iodophenyl)adamantanc,1371 the resultant hyperbranched polybromide (e.g., 25) possessed enhanced solubility in the above solvents, possibly as a result of the disruption of crystallinity and increased porosity. 

Amino-2-(4-aminophenoxy)-p5uidine is another type of diamine for organically soluble wholly aromatic PAs. The basic structure of the PA is not very much changed. Note that 5-amino-2-(4-aminophenoxy)-pyridine is very similar to 4,4 -diaminodiphenyl ether. Obviously, it is sufficient in introduce asymmetry into the molecule to achieve solubility. The thermal properties of the resulting aramids are essentially unchanged. 

Some aramids are processed from isotropic solutions. Flexible chain homo-polymers like MPDI can be dissolved in solvents like NMP and DMAc [88] to form such solutions but the degree of solubility can be further enhanced by copolymerization [83]. Isotropic solutions can be also obtained with p-aramids but in this case copolymerization is required to enhance solubility. 

Poly(p-phenyleneterephthalamide) is soluble in dimethyl sulfoxide and is used to produce the well-known Aramid fibers. A blend of this material and polypyrrole in the form of film was prepared by the electrode coating method and using a / -toluenesulfonate salt as electrolyte [82]. A comparison of the mechanical properties of the blend with pure polypyrrole showed that the blend is a tougher material with a higher modulus and lower elongation at break. Treatment of the blend with HCl raises the conductivity but also increases hardness and toughness. 

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