Alkoxylation of PU Polymer

Urethane groups react with alkyleneoxides [(propylene oxide (PO), ethylene oxide (EO)], by the addition of epoxy compounds to the -NH- group containing active hydrogen, from the urethane groups. 

It is very interesting that in the alkoxylation (with PO or EO) of a flexible or semiflexible PU foam, the PU crosslinked polymer is transformed into a liquid product. 

The scission of urethane groups is explained by the following two consecutive reactions (20.13 and 20.14). The first reaction is the addition of alkylene oxide to the active hydrogen of urethane groups (20.13). The resulting hydroxyalkyl urethane, by an intramolecular transesterification, leads to the splitting of the urethane bonds of PU, the PU network is destroyed with the formation of an oxazolidone and a polyether polyol. 

The alkoxylation process is easy to apply to PU foams having a low concentration of urethane and urea groups such as flexible and semiflexible foams, integral skin foams, PU elastomers and so on. Urea groups react in a similar way with urethane groups, with the formation of oxazolidones and amines by an intramolecular alcoholysis of urea groups (reaction 20.15). 

In Sections 20.1-20.4 the main reactions involved in the chemical recovery of PU wastes i.e., hydrolysis, glycolysis, aminolysis and alkoxylation reactions were presented. Several important processes for chemical recovery of PU polymers will be presented in the next chapters. 

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