Amines cyclic initiation with Lewis acids

After the amines, acid anhydrides constitute the next most commonly used reagents for curing epoxy monomers. The epoxy-acid reaction proceeds through a stepwise mechanism (Sec. 2.2.4) while the reaction of epoxides with cyclic anhydrides, initiated by Lewis bases, proceeds through a chain-wise polymerization, comprising initiation, propagation, and termination or chain transfer steps. Some of the postulated reactions are shown in Table 2.25 (Matejka et al., 1985b Mauri et al., 1997). 

In cationic polymerizations, electron-deficient initiators (mostly Bronsted or Lewis acids) react with electron-rich monomers. The active chain end (ACE) bears a positive charge with the active sites being either carbenium or 0x0-nium ions. Molecular weights are often limited by the inherent sensitivity to impurities, chain transfer, and rearrangement reactions. Suitable monomers for cationic polymerizations are vinyl monomers with electron-donating moieties or cyclic structures containing heteroatoms, while the latter case is termed cationic ROP. Eligible monomers include cyclic ethers, acetals, and amines as well as lactones and lactams (Scheme 3). 

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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