Polymers, living carbanionic

Interest in anionic polymerizations arises in part from the reactivity of the living carbanionic sites4 7) Access can be provided to polymers with a functional chain end. Such species are difficult to obtain by other methods. Polycondensations yield ro-functional polymers but they provide neither accurate molecular weight control nor low polydispersity. Recently Kennedy51) developed the inifer technique which is based upon selective transfer to fit vinylic polymers obtained cationically with functions at chain end. Also some cationic ring-opening polymerizations52) without spontaneous termination can yield re-functional polymers upon induced deactivation. Anionic polymerization remains however the most versatile and widely used method to synthesize tailor made re-functional macromolecules. 

The reaction of an unsaturated compound with an antagonist function located at the end of a polymer chain is still the most commonly used method to synthesize macromonomers. We have already mentioned some processes that can be used to introduce into the chain end of a macromolecule a functional group, e.g. by deactivation of living carbanionic sites and transfer reactions of various kinds in cationic polymerization. We have also described some methods used to link an active terminal double bond to the chain end originally bearing hydroxy groups. 

Polymeric organolithium compounds exhibit limited stability in ether solvents similar to alkyllithium compounds. Living carbanionic polymers react with ether solvents such as THF in a pseudo-tirst-order decay process and the rate decreases in the order Li > Na > K. For example, a 10 M solution of poly(styryl)lithium in THF at 25 °C exhibited a rate of decay of a few percent per minute, but poly(styryl)cesium was found to be exceptionally stable [96], Metalation and decomposition reactions can also occur in the presence of amines such as TMEDA. 

In the termination step, the living carbanionic polymer can be deactivated by proton abstraction from protic solvent, by which process the end of the polymer is saturated. 

Tonhauser C, Frey H (2010) A road less traveled to functional polymers epoxide termination in living carbanionic polymer synthesis. Macromol Rapid Commun 31 1938-1947... 

It is claimed that many types of reactions can be performed more easily with multiple polymers. To avoid undesirable side reactions two reacting species can be used with each attached to a different polymer. Such polymer-bound reactants can coexist in the same reaction vessel without interacting. An example is the preparation of benzoyl acetonitrile by Patchomik and coworkers. Molecules of triphenylmethane lithium, attached to polystyrene supports, were combined with also immobilized o-nitrophenol. The < -nitrophenols were prereacted with benzoyl chloride. The two species were combined and acetonitrile molecules containing acidic hydrogens were introduced into the reaction mixture. This resulted in hydrogens being abstracted from the introduced molecules and formation of short-lived carbanions ... 

In 1997 Khauss et al. presented an elegant synthesis to star polymers with a hyperbranched core and (hyp>er)branched materials by slow addition of a suitable termimer (or a mixture of monomer and termination agent) to living, carbanionic polymer chains ( convergent anionic polymerization ).By this technique, a variety of different macromolecular architectures can be synthesized with moderate polydispersities. 

In contrast to many other functionalization reactions, termination of living carbanionic polymers with ethylene oxide (Eq. 19) is relatively... 

Alkyllithitim-initiated, anionic polymerization of vinyl monomers is a very useful synthetic method since the major variables affecting polymer properties can generally be controlled, e.g., molecular weight, molecular weight distribution, copolymer structure and composition, configurational microstructure, molecular architecture, and chain-end functionality. This control is a direct consequence of the fact that in the absence of reactive impurities many of these polymerizations are termination and chain transfer free therefore, the products of these polymerizations are living polymers" with carbanionic chain ends. 

A further limitation with respect to the coupling reaction is the requirement that the living carbanionic polymers utilized must be sufficiently reactive to undergo facile addition reactions to 1,1-diphenylethylene units. In practice, this means that the first arms are limited primarily to styrene- and diene-type monomers. 

Burchard (Scheme 2) recently developed an approach to synthesize star-shaped polymers with tertiary amine groups at the outer end of the branches [30]. The polymerization of styrene was initiated with ((3-dimethylamino)propyl)lithium and the living carbanions were reacted stoichiometrically with tris(allyloxy)-1,3,5-triazine (TT). 

Formation of block polymers is not limited to hydrocarbon monomers only. For example, living polystyrene initiates polymerization of methyl methacrylate and a block polymer of polystyrene and of polymethyl methacrylate results.34 However, methyl methacrylate represents a class of monomers which may be named a suicide monomer. Its polymerization can be initiated by carbanions or by an electron transfer process, the propagation reaction is rapid but eventually termination takes place. Presumably, the reactive carbanion interacts with the methyl group of the ester according to the following reaction... 

Szwarc, M. Carbanions, living polymers and electron transfer process. New York Inter-science 1968... 

The observation of Tsuji et al. 148) concerned with copolymerization of 1- or 2-phenyl butadiene with styrene or butadiene illustrates again the importance of the distinction between the classic, direct monomer addition to the carbanion, and the addition involving coordination with Li4. The living polymer of 1- or 2-phenyl butadiene initiated by sec-butyl lithium forms a block polymer on subsequent addition of styrene or butadiene provided that the reaction proceeds in toluene. However, these block polymers are not formed when the reaction takes place in THF. The relatively unreactive anions derived from phenyl butadienes do not add styrene or butadiene, while the addition eventually takes place in hydrocarbons on coordination of the monomers with Li4. The addition through the coordination route is more facile than the classic one. 

Shima M, Smid J, Szwarc M (1964) J. Polymer Sci. Polym. Lett. 2 735 Szwarc M (1968) Carbanions, Living Polymers and Electron Transfer Processes. Wiley Publ. 

Poly (alkyl methacrylate) macromonomers are formed by reaction of the living polymer with VBC. This method was shown to be free of side reactions and quantitative, in spite of the low nucleophilicity of the carbanionic site involved 72,75). 

M. Szwarc, Carbanions, Living Polymers and Electron Transfer Processes, Interscience, New York, 1968. 

Szwarc, M. "Carbanions, Living Polymers, and Electron Trans-... 

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