In polymer chemistry, anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but traditionally vinyl monomers are used. Often anionic polymerization involves living polymerizations, which allows control of structure and composition.
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. Twenty years later, living polymerization was demonstrated by Michael Szwarc and coworkers. 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." An important aspect of his work, Szwarc employed the aprotic solvent tetrahydrofuran. Being a physical chemist, Szwarc elucidated the kinetics and the thermodynamics of the process in considerable detail. At the same time, he explored the structure property relationship of the various ion pairs and radical ions involved. This work provided the foundations for the synthesis of polymers with improved control over molecular weight, molecular weight distribution, and the architecture.
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. This sparked the development of commercial anionic polymerization processes that utilize alkyllithium initiators.
Roderic Quirk won the 2019 Charles Goodyear Medal in recognition of his contributions to anionic polymerization technology. He was introduced to the subject while working in a Phillips Petroleum lab with Henry Hsieh.
Two broad classes of monomers are susceptible to anionic polymerization.
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End groups are an important aspect of polymer synthesis and characterization. In polymer chemistry, they are functional groups that are at the very ends of a macromolecule or oligomer (IUPAC). In polymer synthesis, like condensation polymerization and free-radical types of polymerization, end-groups are commonly used and can be analyzed by nuclear magnetic resonance (NMR) to determine the average length of the polymer. Other methods for characterization of polymers where end-groups are used are mass spectrometry and vibrational spectrometry, like infrared and raman spectroscopy.
In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are sometimes called bipolymers. Those obtained from three and four monomers are called terpolymers and quaterpolymers, respectively. Copolymers can be characterized by a variety of techniques such as NMR spectroscopy and size-exclusion chromatography to determine the molecular size, weight, properties, and composition of the material.
In polymer chemistry, living polymerization is a form of chain growth polymerization where the ability of a growing polymer chain to terminate has been removed. This can be accomplished in a variety of ways. Chain termination and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation. The result is that the polymer chains grow at a more constant rate than seen in traditional chain polymerization and their lengths remain very similar (i.e.
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