Living coupling reaction

Y.C. Bae, Z. Fodor, and R. Faust, Living coupling reaction in living cationic polymerization. 1. Coupling reaction of living polyisobutylene, Macromolecules, 30(2) 198-203, January 1997. 

The synthesis of hetero-arm star-block copolymers with well-controlled architecture such as AnBn- or ABC-type star-block copolymers, recently accomplished by a living anionic process utilizing a novel concept of the living coupling reaction [84], however, has been a challenge by a living cationic process. 

Scheme 10 Living coupling reaction of living PIB with BDTEP and chain ramification reaction of MeVE for the synthesis of A2B2 star-block copolymer...

As a proof of the concept, an amphiphilic A2B2 star-block copolymer (A = PIB and B = PMeVE) has been prepared by the living coupling reaction of living PIB followed by the chain ramification polymerization of MeVE at the junction of the living coupled PIB as shown in Scheme 26.5 [136]. 

Liu, M., Britt, P.F. and Mays, J.W. (2004) Synthesis of amphiphihc miktoarm star copolymers A2B2 of polystyrene and poly( ethylene oxide). ACS Polym. Prepr. (Div. Polym. Chem.), 45(2), 555-556. Bae, Y.C. and Faust, R. (1998) Living coupling reaction in hving cationic polymerization. 2. Synthesis and characterization of amphiphihc A2B2 star-block copolymer PlB-star-bis (methylvinyl ether). Macromolecules, 31,2480-2487. 

Although the effective functionality of CISi-PaMeSt was less than one, attempts were made to obtain block copolymers by coupling with living polyisoprenyllithium and a,w-disodium polyisobutylene glycolate. These particular coupling reactions were selected because it is known that Si-Cl bonds readily react with organolithium compounds and sodium alkoxides43 45 . 

An iterative approach involving coupling reactions of living anionic polymers followed by functionalization, leads to three generation homo- and block copolymers. [208]. The reactions used are shown in Scheme 115. 

LCB polymers can be formed by chemically linking preformed polymers (arm first or polymer first method) or by growing polymer chains from a multifunctional initiatior (core first method). In both cases living polymerization techniques are preferred because they provide better control over MW, MW distribution and the final branching architecture. However, highly selective coupling reactions e.g. with multifunctional isocyanates, or dicyclohexylcar-bodiimide (DCC) coupling, have also been successful. 

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