Epoxy-amine reaction, alternating

Like phenols, thiols also react with epoxide groups to form hydroxyl sulfides as shown in reaction (81). It was originally believed that thiols are unreactive with epoxides. However, it has been shown recently that, in the presence of suitable catalysts, epoxy-thiol reactions are several times faster than epoxy-amine reactions, particularly at low temperatures. Reaction (81) is very selective and no side reactions have been observed in this case. The reaction has been found to be accelerated by the presence of amines and two alternative reaction routes have been suggested to explain the formation of sulfide ion intermediate (Schemes 27 and 28), which then reacts with the thiol. 

Another usual family of hardeners employed to cure epoxy monomers are cyclic anhydrides, with the reaction initiated by tertiary amines or ammonium salts. The reaction proceeds through an alternating chainwise copolymerization, as shown in Figure 28.3. 

In the conventional curing processes of epoxy resins, the crosslinks developed are of a single strand structure involving ether or amine extension points. The object of this study is the formation of the oxazolidone ring which by reaction of epoxy and isocyanate groups, affords an alternative type of crosslink, which it was anticipated will have a significant influence on the T of the cured epoxy resin. 

A cyclic anhydride, such as phthalic anhydride or maleic anhydride, will form a nearly 1 1 alternating copolymer with alkylene oxides. This reaction is the same one used in the curing (hardening) of epoxy resins. A large number of initiators can be used for this reaction, including tertiary-amines, various Lewis acids, and bases including alkoxides. The uncatalyzed reaction invokes initiation with a hydroxyl group (125,126). This reaction can be used to introduce a polyester unit into a polyether polymer chain. With phthalic anhydride, the reaction proceeds as follows ... 

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