Polymers, carbanionic coupling reactions

Difunctional initiators such as sodium naphthalene are useful for producing ABA, BABAB, CAB AC, and other symmetric block copolymers more efficiently by using fewer cycles of monomer additions. Difunctional initiators can also be prepared by reacting a diene such as /n-diisoprope ny I benzene or l,3-bis(l-phenylethenyl)benzene with 2 equiv of butyl-lithium. Monomer B is polymerized by a difunctional initiator followed by monomer A. A polymerizes at both ends of the B block to form an ABA triblock. BABAB or CABAC block copolymers are syntehsized by the addition of monomer B or C to the ABA living polymer. The use of a difunctional initiator is the only way to synthesize a MMA-styrene-MMA triblock polymer since MMA carbanion does not initiate styrene polymerization (except by using a coupling reaction—Sec. 5-4c). 

Coupling Reactions of Carbanionic Polymers by Elemental Compounds Such as Oxygen and Sulfur... 

The technique of the sulfur coupling reaction can be used also to prepare multiblock polymers. The technique of deactivation of carbanionic polymer with oxygen or sulfur is able to yield numerous interesting organic compounds such as novel macromolecular initiators, new macromolecular additives, and telechelic polymers. Finally, the coupling reactions can be used to build block polymers. 

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. 

Anionic polymerizations are well suited for the synthesis of polymers fitted at chain end with reactive functions. Block copolymers can result from reactions between suitable functions carried by two different functional precursors. In some cases the carbanionic sites themselves are the reactive functions. In other cases, functional polymers (obtained anionically, or by other methods) can be reacted with low molecular weight coupling agents. Here are a few examples ... 

Coupling of polymers to form graft copolymers is accomplished by nucleophilic reaction between living polystyryl carbanion and various chlorine-containing polymers such as... 

In this paper we describe the reaction between carbanionic ends of oligomers or polymers and elemental compounds such as oxygen and sulfur we observe two sets of reactions coupling and functionalization. 

Polymer-supported carbanion equivalents are the obvious supplement to polymer-supported access to reactive electrophiles either by oxidizing polymers or by release of carbenium ions. The combination of an oxidizing resin with a support carrying carbanion equivalents will be especially rewarding, enabling reaction sequences with C-C coupling steps and thus opening access to a wealth of potentially relevant products. 

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