Cyclization during thermal degradation

In polyamide 66, the cyclization reaction within the chain that leads to cyclo-pentanone derivatives and amines represents the most important reaction during thermal degradation, Fig. 4.67. 

Side reactions that might occur during direct polyesterification include loss of functionality by decarboxylation of an acidic end group, thermal degradation of ester linkE es, the formation of ether linkages, and cyclization reactions. 

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