Highly branched aromatic polymers polyesters

Preparation and characterization of highly branched aromatic polymers, polyphenylenes, polyesters, polyethers, and polyamides, were reviewed. These polymers were prepared from condensation of AB -type monomers, which gave noncrosslinked, highly branched polymers. The polymer properties are vastly different compared to their linear analogs due to their resistance to chain entanglement and crystallization. 

Dendritic polymers are used as functional thin layers. Highly branched aromatic polyesters with polar end groups show good response behaviour in gas phase and liquid sensors [46]. Ease of recycling of the expensive platinum complexes (e.g. by nanofiltration) is a positive aspect of the use of such sensor den-drimers [47]. 

Because of their uncomplicated syntheses, aromatic polyesters are the most widely studied class of highly branched polymers. The polyesters were prepared in a single step by condensation polymerization from aliphatic dihydroxy monoacids or by stepwise syntheses. 

Not only good solubility but also solution behavior differs for hyperbranched polymers compared with linear polymers. Hyperbranched polymers such as hyperbranched aromatic polyesters (12,13) exhibit a very low a-value in the Mark-Houwink-Sakurada equation and low intrinsic viscosities. This is consistent with highly branched and compact structures. A comparison has been made between linear polymers, h5q)erbranched polsrmers, and dendrimers with respect to... 

The saturated polyesters that find conunercial applications are mostly linear, except for some specially prepared branched polymers used in the preparation of polyurethanes. The linear polyesters became commercially important materials early in this century and still find many uses in industry. The earliest studies reported condensations of ethylene, trimethylene, hexamethylene, and de-camethylene glycols with malonic, succinic, adipic, sebacic, and orthophthalic acids. Later studies showed that such condensations yield high molecular weight compounds. Nevertheless, these polyesters exhibit poor hydrolytic stability and are generally low-melting. Subsequently, however, it was found that aromatic dicarboxylic acids yield polymers with high melting points, and poly(ethylene terephthalate), which melts at 265 C, is now an important commercial material. 

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