Anionic addition polymerization

[2][3] As early as 1936, Karl Ziegler proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination.

[5][6] In one of the breakthrough events in the field of polymer science, Szwarc elucidated that electron transfer occurred from radical anion sodium naphthalene to styrene.

The results in the formation of an organosodium species, which rapidly added styrene to form a "two – ended living polymer."

[7] The use of alkali metals to initiate polymerization of 1,3-dienes led to the discovery by Stavely and co-workers at Firestone Tire and Rubber company of cis-1,4-polyisoprene.

[3] Roderic Quirk won the 2019 Charles Goodyear Medal in recognition of his contributions to anionic polymerization technology.

In order for polymerization to occur with vinyl monomers, the substituents on the double bond must be able to stabilize a negative charge.

Highly electrophilic monomers such as cyanoacrylates require only weakly nucleophilic initiators, such as amines, phosphines, or even halides.

[3] The solvents used in anionic addition polymerizations are determined by the reactivity of both the initiator and nature of the propagating chain end.

Polar solvents are necessary for this type of initiation both for stability of the anion-radical and to solvate the cation species formed.

[3] Monomers activated by strong electronegative groups may be initiated even by weak anionic or neutral nucleophiles (i.e. amines, phosphines).

One of the remarkable features of living anionic polymerization is that the mechanism involves no formal termination step.

[8] Synthesis of block copolymers is one of the most important applications of living polymerization as it offers the best control over structure.

Moreover, this strategy, enables synthesis of linear block copolymer structures that are not accessible via sequential monomer addition.

[12] In this case, the functional groups are protected since the ends of the anionic polymer chain is a strong base.