Poly (arylene ether) s and Poly (arylene ether ketone) s
High-performance polymeric material are poly (arylene ether) s and poly (arylene ether ketone) s. They can be used as structural resins because in composite fabrications they offer an attractive combination of chemical, mechanical, and physical properties.
Commercial poly (ether ketone) s that are also poly (arylene ether) s are formed from diacid chloride by the Friedel–Craft reaction [234].
Similar polyketones form from dicarboxylic acids rather than dicarboxylic acid chlorides, when P2O5—methanesulfonic acid is used as a catalyst [235]. All these materials form a group of tough, high melting resins.
Some current preparations of poly (arylene ether) s are carried out by nucleophilic displacements of activated aromatic dihalides or dinitro groups by alkali metal bisphenates. The reactions take place in polar aprotic solvents. The glass transition temperatures, tensile strengths, and tensile moduli of these materials tend to increase when heterocyclic units are incorporated into the backbones. Poly (arylene ether) s containing imide [236], phenylquinoxaline [237–239], imidazoles [240], pyrazoles [241], 1,3,4-oxadiazoles [240], benzoxazoles [240], and benzimidazoles [240] groups were prepared.
The preparation of such polymeric materials can be illustrated as follows [241]:
where R = H, Ph; X = Cl, F; Y = carbonyl, sulfone, or a diketone aryl group. The above shown medium and high molecular weight polymers exhibit good solubility in solvents like dimethyl acetamide and good thermal stability. The same is true of the other poly (arylene ether) s mentioned above. As a result, these high-performance thermoplastics have the potential of being useful in low-cost composite fabrications.
One paper [242] describes preparation of poly (imidoaryl ether ketone) s and poly (imidoaryl ether sulfone) s that exhibit particularly good heat stability. The synthesis can be illustrated as follows:
where: R = CH3;CH3(CH2)11; Phenyl; X = SO2; CO; Isophthaloyl; Based on thermogravimetric analyses, the phenyl substituted polymers lose only 10% of their weight in air and in nitrogen at 550C. In addition, the polymers have high glass transition temperatures and remain soluble in common solvents, like chloroform and methylene chloride. These are high molecular weights polymers that can be cast from solution to give tough, flexible films [242].
