Side Reactions in Polyesterification

During the polyesterification reactions, especially at higher temperatures, it is possible to have some undesired side reactions take place, such as formation of terminal double bonds, formation of aldehydes, formation of polyenes which lead to coloured polyesters and loss of functionality. 

Reactions 8.21 and 8.22 lead to loss of functionality and reaction 8.21 to increase of acidity. 

The molecular weight distribution (MWD) of polyester polyols is broader than that of polyether polyols. The polydispersity index (PDI) of high MW polyester polyols (e.g., 2000 daltons) is around 2.8. 

All polyester polyols have in their composition a very small quantity of low MW cyclic polyesters. Non-fogging polyesters for the automotive industry were obtained by thin film distillation in high vacuum of finished polyesters. In this way the low MW, volatile species and cyclic oligomers were eliminated [1]. 

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