ABCD Miktoarm Star Polymers

In addition to several examples of ABC stars synthesized by the Uving/controUed polymerization systems mentioned above, three different ABCD p-star polymers were synthesized almost at the same time in 2008 using very similar methodologies (combining living/controlled polymerization systems with click chemistry) (Wang et al., 2008 Altintas et al., 2008), and (Yang et al., 2008). 

Tunca et al. synthesized two different ABCD star-branched polymers with PS (A), PaCL (B), PMMA (C), and P BA or PEO as the D segment by linking between an in-chain-propargyl-functionalized AB block copolymer and an in-chain-N3-functionalized CD block copolymer in the cUck manner. The resulting polymers were 13 000 g/mol and 16 000 g/mol in M value 1.2). Pan et al. synthesized both ABC and ABCD stars 

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Scheme 4.4 Synthesis of 3-arm ABC, 4-arm ABCD, and 5-arm ABCDE miktoarm star polymers with PMPVS or PA segments using intermediate polymer anions.

Scheme 4.10 Successive synthesis of 3-arm ABC and 4-arm ABCD miktoarm star polymer by the iterative methodology using 6.

Scheme 4.16 Synthesis of 4-arm ABCD miktoarm star polymers by using 10.

Scheme 4.19 Synthesis of 4-arm ABCD miktoarm star polymers by combination of living anionic polymerization, living/controlled radical polymerization, and click reaction.

The term miktoarm (from the greek word fu/crog, meaning mixed), or heteroarm star polymers, refers to stars consisting of chemically different arms. In the past decade considerable effort has been made toward the synthesis of miktoarm stars, when it was realized that these structures exhibit very interesting properties.88-90 The synthesis of the miktoarm star polymers can be accomplished by methods similar to those reported for the synthesis of asymmetric stars. The chlorosilane, DVB, and DPE derivative methods have been successfully employed in this case. Furthermore, several other individual methods have appeared in the literature. The most common examples of miktoarm stars are the A2B, A3B, A2B2, kn >n (n > 2) and ABC types. Other less common structures, like the ABCD, AB5, and AB2C2 are now also available. 

The method was subsequently extended to the synthesis of A2B2 milktoarm copolymer and ABCD miktoarm star quarter-polymer. Since then, many groups have reported the synthesis of miktoarm stars with a great variety of monomers. Recendy,... 

Yang, L., Zhou, H., Shi, G. et al. (2008) Synthesis of ABCD 4-miktoarm star polymers by combination of RAFT, ROP, and cUck chemistry . Journal of Polymer Science Part A-Polymer Chemistry, 46,6641-6653. 

In conclusion, we have been able to use the assembly or association and reaction strategy to prepare miktoarm copolymers. For this particular system, we could separate the pure miktoarm star polymers from their precursors by fractionation precipitation. We are now working on the preparation of p-ABC and p-ABCD polymers from this technique and are exploring the applications of the p-ABC or p-ABCD polymers produced. 

Several excellent books and review articles have been published covering this particular area of polymer science [1-3]. Nevertheless, this review will highlight recent (2000-2004) advances and developments regarding the synthesis of block copolymers with both linear (AB diblocks, ABA and ABC triblocks, ABCD tetrablocks, (AB)n multiblocks etc.) and non-linear structures (star-block, graft, miktoarm star, H-shaped, dendrimer-like, and cyclic copolymers). Attention will be given only to those synthetic methodologies which lead to well-defined and well-characterized macromolecules. 

Miktoarm polymers are essentially heteroarm star polymers where two or more arms of the star are chemically unique. Therefore, the same general approaches for the synthesis of star polymers also apply to miktoarms, with some additional constraints. Many research groups have sequentially performed orthogonal polymerization techniques to access a variety ABC and ABCD miktoarm polymers, in a core-first approach. 

Altintas, O., Hizal, G., and Tunca, U. (2(X)8) ABCD 4-miktoarm star quaterpolymers using click [3 + 2] reaction strategy. Journal of Polymer Science Part A-Polymer Chemistry, 46,1218-1228. 

Wang, X., He, J., and Yang, Y. (2007) Synthesis of ABCD-type miktoarm star copolymers and transformation into zwitterionic star copolymers. Journal of Polymer Science Part A-Polymer Chemistry, 45,4818-4828. 

Chlorosilanes were used applying an identical reaction procedure to prepare either quaterarm pol)miers of type ABCD or 4- miktoarm polymers of type A2B2. A, B, C, D correspond to PS, PBd, PI, and poly(4-methylst5n ene), respectively [33]. That method was extended recently to well-defined poly(iso-prene)/poly(butadiene) A2B2 copolymers [34]. The presence on the same nodu-lus of chains exhibiting different chemical structures leads to original solution properties. Roovers et al. [35] have examined in detail the solution properties and compared the specific behavior of these miktoarm star-shaped polymers to linear diblock copolymers. That strategy was extended to the preparation of... 

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