Polyester derived from aromatic diacids

The probable mechanism for conductance in selected polymers is related to the difficulty of delocalizing electrons. Carraher and colleagues found that antimony polyesters derived from aliphatic diacids are weak semiconductors with bulk specific resistivities in the range of 10"10 ohm cm, whereas analogous polyesters derived from aromatic diacids are good semiconductors with bulk resistivities of about 10"4 ohm cm. The difference in electron conductivity is believed to be due to a difference in ability of the material to delocalize electrons the aromatic polyesters possess the ability to delocalize electrons throughout the polymer chain and thus are more conductive (lower resistivities). 

TABLE 4. POLYESTERS DERIVED FROM AROMATIC DIACIDS ... 

Thermotropic polyesters derived from unsubstituted aromatic diols and diacids usually have melting points which approach or exceed the thermal decomposition point. Thus it is reasonable to expect that some modification in molecular structure would be required to render them melt-processable, even though some adverse effects on liquid crystallinity and mechanical properties of the polymers would result. 

This is the preferred method for the synthesis of both, aliphatic and aromatic polyesters derived from CHDM. The reaction is usually accomplished in two steps. The first step is carried out under a pressure which depends on the diacid or the dimethyl ester derivative used for the synthesis. Usually an excess of diols to diacid (1.2-2.2 1) is employed so a mixture of short oligomers is produced. In the second polycondensation step, which is carried out at higher temperatures and under vacuum, the oligomers react to generate the polymer and the excess of diol is removed. If the resulting polyester is crystalline it may be subjected to solid state postpolycondensation (SSP) in order to increase the molecular weight. 

Class A Fiber grade or engineering type polyesters with high melt point and molecular weight, derived wholly from aromatic diacids, diols, and hydroxy acids. 

A number of methods are available for the preparation of aromatic polymers. The majority of these methods involve the formation of a chemical bond between a carbon atom and a heteroatom. Typical of these are, for example, aromatic polycarbonates the latter are prepared by the reaction of a dihydric phenol with phosgene or derivative thereof.The polymerization proceeds via formation of a carbon-oxygen bond. A similar situation is encountered with the class of polyarylates — the polyesters from dihydric phenols and aromatic diacids. " ... 

Ester bond-hastd polymers, called polyesters, include several biodegradable and nonbiodegradable polymers such as polyethylene terephthalate (PET), polybutylene terephthalate, polybutylene succinate, polycaprolactone, polylactic acid, polyhydroxyalcanoate and aromatic-aliphatic polyesters. They are derived from starting monomers such as dialcohol, diacid and/or their esters (like methyl esters), and hydroxyl acids that are monomers with both an alcoholic and a carboxylic functional group. All such monomers react to form ester bonds with the release of water (or methanol if the starting monomers are the methylic esters of diacids). 

It is this last class of polyesters that finds use in hot melt adhesives. The compositions and properties of the available polyesters varies widely and fall between Class A and Class B polymers typically they are derived from aliphatic diols and aromatic diacids, notably tere-phthalic acid, and are synthesized to fairly high molecular weight, between 10,000 and 30,000. 

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