Ladder Type polymers with heterocyclic Structure

2 LADDER TYPE POLYMERS WITH HETEROCYCLIC STRUCTURE - General aspects 

Ladder polymers have their backbone made from an interrupted series of condensed rings. In such polymers, very frequently the rings contain heteroatoms, and the polymer can be considered as part of the class of polymers with heterocycles in the main chain. One of the first synthesized polymers from this class was obtained from the oxidation and heating of polyacrylonitrile [1, 2]. Multifunctional condensations also can lead to ladder polymers. For example, a poly(phenoxazine) is formed from the reaction of a substituted quinone and a diaminodihydroxybenzene as shown below  

Polymers from various other groups have a ladder type backbone. Most of these polymers have good thermal resistance since they frequently contain aromatic bonds 

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In general, the types of polymers which have the best thermal properties are aromatic in character (often with recurring heterocyclic units), have low hydrogen content, and often have stepladder or ladder structures. Although there are numerous articles in the literature which deal with the effects of structure on stability within a given class of heat-resistant polymers, only a limited number of publications are to be found which compare the stabilities of different classes of heat-resistant polymers under controlled conditions. From Ehler s TGA studies on different classes of heat-resistant polymers, as well as from other sources, a classification can be made of the effects of structure on heat stability for several classes of compounds. For... 

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