Polyetherification reaction mechanism

Figure 14 shows that the difference in the result obtained by the combination of the kinetic and statistical method and by the purely statistical method is rather large. In real systems, the polyetherification reaction may be complicated by termination reactions e.g. by chain transfer, so that the mechanism may deviate from the... 

For catalysis by bases, addition esterification is the first and the fastes reaction. It can be followed by slower polyetherification reaction, if epoxy groups are in excess, or by condensation esterification (even slower), if carboxyl groups are in excess. This mechanism was verified on a model system caproic acid — phenylglycidyl ether... 

Scheme 3 General mechanism for amine cure of epoxy resins involving (a) primary and (b) secondary amines (c) hydroxyl catalyzed polyetherification reaction. This is shown for one functional group R and R denote the other half of an aryl or alkyl backbone.

Although the major interest in experimental and theoretical studies of network formation has been devoted to elastomer networks, the epoxy resins keep apparently first place among typical thermosets. Almost exclusively, the statistical theory based on the tree-like model has been used. The problem of curing was first attacked by Japanese authors (Yamabe and Fukui, Kakurai and Noguchi, Tanaka and Kakiuchi) who used the combinatorial approach of Flory and Stockmayer. Their work has been reviewed in Chapter IV of May s and Tanaka s monograph Their experimental studies included molecular weights and gel points. However, their conclusions were somewhat invalidated by the fact that the assumed reaction schemes were too simplified or even incorrect. It is to be stressed, however, that Yamabe and Fukui were the first who took into account the initiated mechanism of polymerization of epoxy groups (polyetherification). They used, however, the statistical treatment which is incorrect as was shown in Section 3.3. 

---