Starters for rigid polyether polyols

Unfortunately, it is a difference between a starter, such as nonylphenol, or a fatty alcohol, which have only one type of hydroxyl group and polyols. Some polyols used as starters for rigid polyether polyols have in the same molecule various types of hydroxyl groups (for example, primary hydroxyls and secondary hydroxyls) which do not have equivalent reactivities in the alkoxylation reactions. For example, sorbitol has two primary hydroxyls and four secondary hydroxyls, sucrose has three primary hydroxyls and five secondary hydroxyls. In both polyols, the secondary hydroxyls have different substituents and they are not totally equivalent. TMP, pentaeriythritol and dipentaerythritol have only one type of equivalent primary hydroxyl group. Thus, the initiation reaction (reaction of PO with hydroxyl groups of starter) is in fact the sum of the reactions of PO with each type of hydroxyl group of the starter ... 

Resol resins, having very reactive methylol groups (obtained by the condensation of phenol with formaldehyde in basic media), are rarely used as starters for rigid polyether polyols. One reason is the impossibility of melting these resins at the propoxylation temperature, because upon heating they rapidly polycondensate and crosslink. An interesting representative of this group of resin is trimethylol phenol (reaction 15.26). 

Sucrose, the most important starter for rigid polyether polyols is produced exclusively by extraction from naturally resources (Figure 17.1) [1]. 

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