polymerize the monomers in classes B, C, and D, but they cannot initiate the polymerization of monomers in class A. The initiators in class c can polymerize both C and D class monomers, while they are inert for the monomers in classes A and B. The least-reactive initiators in class d, such as amines and phosphines, undergo anionic polymerization of the most-reactive D class monomers Among the monomers, α-cyanoacrylate is polymerized, even with water.The relationship between a monomer and its growing chain-end anion is also important in order to understand anionic polymerization behavior. In general, the most-reactive chain-end anions derive from the least-reactive monomers and vice-versa, because they are conjugated bases and acids with each other. For example, when considering styrene (class A) and methyl methacrylate (MMA) (class B), the latter is more reactive than the former because the electron density on the C=C bond of MMA is considerably reduced by the electron-withdrawing ester carbonyl group, whereas that on the styrene C=C bond is influenced much less by the phenyl group. On the other hand, the chain-end anion derived from MMA is also reduced in electron density by the same electron-withdrawing effect, and becomes less reactive than that derived from styrene. In practice, the chain-end anion from MMA has no ability to polymerize styrene, whilst the chain-end anion from styrene can polymerize styrene and, of course, the more-reactive MMA. Thus, the monomers in class A will always produce the most reactive growing chain-end anions that can polymerize all monomers in classes A, B, C, and D. In contrast, the least-reactive chain-end anions derived from the most-reactive monomers in class D can polymerize only the monomers in class D. These relationships are very important -even critical -for selecting the correct anionic initiator in polymerization, as well as when synthesizing block copolymers.