Benzene rings aromatic polyesters

Poro-xylene is an industrially important petrochemical. It is the precursor chemical for polyester and polyethylene terephthalate. It usually is found in mixtures containing all three isomers of xylene (ortho-, meta-, para-) as well as ethylbenzene. The isomers are very difficult to separate from each other by conventional distillation because the boiling points are very close. Certain zeoHtes or mol sieves can be used to preferentially adsorb one isomer from a mixture. Suitable desorbents exist which have boiling points much higher or lower than the xylene and displace the adsorbed species. The boihng point difference then allows easy recovery of the xylene isomer from the desorbent by distillation. Because of the basic electronic structure of the benzene ring, adsorptive separations can be used to separate the isomers of famihes of substituted aromatics as weU as substituted naphthalenes. 

The glass temperatures of all products fall within the range 130°-160 °C. The partially aromatic polycarbonate has a glass temperature of 150 °C. the partially aromatic PETP has a glass temperature of 75 °C. To determine the ratio of the aromatic to the aliphatic content, we assume four chain links for the benzene rings. Then the polycarbonate has the ratio aromatic/aliphatic links = 4 6, the polyester has a ratio 4 2, and the polyamides (Table I) have a ratio 4 10. Despite the lower aromatic content the glass temperatures of some of the amorphous polyamide are... 

Further reaction then builds up the polymer, which is called polyester and sold under trade names such as Dacron. The planar benzene rings in this polymer make it stiffer than nylon, which has no aromatic groups in its backbone, and help make polyester fabrics crush-resistant. The same polymer formed in a thin sheet rather than a fiber becomes Mylar, a very strong film used for audio and video tapes. 

The chemical resistance of polyester materials is generally limited due to the comparative ease of hydrolysis of the ester groups, but the bisphenol A polycarbonates are somewhat more resistant. This resistance maybe attributed to the shielding of the carbonate group by the hydrophobic benzene rings on either side. The resin thus shows resistance to dilute mineral acids however, it has poor resistance to alkali and to aromatic and chlorinated hydrocarbons. 

A reduction of the melting temperatures of aromatic LC polyesters can also be accomplished efficiently by the partial incorporation of kinked comonomers. Suitable monomers are meta- or ortho-functionalized benzene rings, meta- or ortho-functionalized six-member heterocycles, and 2,5-func-tionalized five-member heterocycles. A frequently used alternative is two benzene rings connected by linking groups such as... 

Table 3 shows that for PE, PP, and Nylon 6, the Vt values are close to the frequencies of the skeletal twisting vibrations. For aromatic polyesters and polyimides, the v, parameters correspond to the vibrations of the benzene ring, in combination with the deformation vibrations of the C-C and C-N bonds. 

Benzene is a volatile, colorless, highly flammable liquid that is consumed as a raw material for the manufacture of phenolic and polyester resins, polystyrene plastics, alkylbenzene surfactants, chlorobenzenes, insecticides, and dyes. It is hazardous both for its ignitability and toxicity (exposure to benzene causes blood abnormalities that may develop into leukemia). Naphthalene is the simplest member of a large number of multicychc aromatic hydrocarbons having two or more fused rings. It is a volatile white crystalline solid with a characteristic odor and has been used to make mothballs. The most important of the many chemical derivatives made from naphthalene is phthalic anhydride, from which phthalate ester plasticizers are synthesized. 

The most familiar condensation polymers arepolyamides.polyesters, andpolycarbonates. Tlie aramids, polyamides in which aromatic rings are joined by amide bonds, are one class of condensation polymer. Heating 1,4-benzenediamine and the acyl chloride of benzene-1,4-dicarboxylic acid (terephthalic acid) gives the aramid Kevlar with loss of hydrogen chloride. 

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