Highly branched aromatic polymers branching

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]. 

Highly branched aromatic polymers prepared by single step syntheses [Y. H. Kim, Macromol. Symp. 1994, 77, 21-33]. 

Highly Branched Stable Aromatic Polymers Synthesis and Applications [Y. Kim, Chapt. 5, pp. 123-156]. 

The kinetic treatment revealed that the reactivity of pendant allyl groups of the prepolymer is approximately equal to that of the monomer. The ratios ri = kii/kii and r2 = kn/kn have been estimated to be 1.0 and 0.9, respectively [67]. A similar result was also observed for the post-copolymerization of DAI prepolymer with ABz [68]. Now, we can conclude that the concept of equal reactivity of functional groups belonging to the monomer and polymer is valid for the radical polymerization of diallyl aromatic dicarboxylates at an early stage of polymerization, at least up to the theoretical gel point. However, in the case of the highly branched prepolymer formed at a late stage of polymerization, i.e. far beyond the theoretical gel point, the reactivity of pendant allyl groups may be reduced by steric hindrance. 

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. 

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. 

Highly branched polymers such as polypropylene and polymers with other links, e.g. poly(oxymethylene), are most readily attacked by atomic oxygen. Perfluorinated polymers, rubber vulcanized with sulfur, and highly aromatic polymers are the most resistant. 

The rapid reaction between atomic oxygen and polymer films is discussed. This typical interface reaction is considerably influenced by the structure of the polymer. All polymers immediately react with atomic oxygen there is no evidence of even short induction periods or autocatalysis. Most readily attacked are highly branched polymers such as polypropylene and polymers with ether links for example, polyformaldehyde. Perfluorinated polymers, rubbers vulcanized with sulphur, and highly aromatic polymers are most resistant (Fig. 22). Oxidation of polymers by atomic oxygen occurs only at or near the surface of the polymer. For this reason the elucidation of the reaction kinetics and mechanism is very difficult. The conventional physico-chemical methods, UV and IR spectroscopy, are in this case inadequate. 

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