ABC Miktoarm Star Polymer

The first example was an ABC p-star polymer composed of poly(tertahydrofuran) (PTHF), poly(l,3-dioxepane) (PDOP), and PS segments and was synthesized by Pan and coworkers in 2002 (Feng and Pan, 2002). The objective star-branched polymer was synthesized by the 

Recently, two different water-soluble ABC p-stars composed of PEO, P BMA, and poly(2-(diethylamino)ethyl methacrylate) arms plus PEO, P BMA, and poly(A/-isopropylacrylamide) arms were synthesized by combining ATRP with click chemistry in a manner similar to that 

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Scheme 4.1 Synthesis of 3-arm ABC miktoarm star polymer by silyl chloride methodology.

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 radical-to-anion transformation was further merged with click chemistry for the synthesis of ABC-type miktoarm star polymers. For this purpose, a trifimctional initiator, namely, propargyl 2-hydroxylmethyl-2-(a-... 

H. Durmaz, F. Karatas, U. Tunca, G. Hizal, Preparation of ABC miktoarm star terpolymer containing polyjethylene glycol), polystyrene and polyjtert butacrylate) arms by combining Diels-Alder reaction, ATR and SFRP routes,/. Polym. Sci., Part A Polym. Chem. 2006, 44, 499-509. 

Durmaz, H., Kaiatas, F., Tunca, U., and Hizal, G. (2(X)6b) Preparation of ABC miktoarm star terpolymer containing polyfethylene glycol), polystyrene, and poly(tert-butylacrylate) arms by combining Diels-Alder reaction, atom transfer radical, and stable free radical polymerization routes. Journal of Polymer Science Part A-Polymer Chemistry, 44,499. 

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.

Deng, G., Ma, D., and Xu, Z. (2007) Synthesis of ABC-type miktoarm star polymers by click chemistry, ATRP and ROP. European Polymer Journal, 43,1179-1187. 

Shi, P.-J., Li, Y.-G., and Pan, C.-Y. (2004) Block and star block copolymers by mechanism transformation X. Synthesis of poly(ethylene oxide) methyl ether/polystyiene/poly(L-lactide) ABC miktoarm star copolymers by combination of RAFT and ROP. European Polymer Journal, 40,1283-1290. 

Recently, Hadjichristidis, Hirao, and coworkers synthesized complex macromolecular chimeras (a Greek term), which include novel multicomponent linear and miktoarm star polymers containing polypeptide blocks based on a high-vacuum technique (Karatzas et al., 2008). Indeed, 3-arm AB2,3-arm ABC, 4-arm A2B2, and 4-arm AB2C were synthesized, where A, B, and C were polypeptides, PS, and PI or poly(a-methylstyrene) (PaMS), respectively (Figure 13.3). 

An ABC miktoarm star terpolymer has a configuration of a C polymer grafted at the junction point of an AB diblock copolymer as depicted in Figure 18.1c, and hereafter we call it p-ABC. Since it is not necessary to account for the order of the sequences of A, B and C blocks in a p-ABC, ithas fewer variables to designate the system than a linear ABC. However, because of the unusual molecular architecture of a p-ABC whose three different block chains possess the same junction, the microdomain morphologies it can take become quite different from those of a linear ABC when they microphase-separate into three phases. (In this chapter, we only consider the three-phase structures.) Three microphases of a p-ABC must meet in space to... 

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. 

The synthesis of four-armed biodegradable star block copolymers of PCL and poly-11 using hydroxyl-terminated four-arm star PCL and a Sn(Oct)2 co-initiation system was also reported. Amphiphilic three ABC-miktoarm star ter-polymers composed of PCL, MPEG, and poly-11 were synthesized by a combination of ROP and click chemistry. 

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. 

In fact,Stadler and co-workers [252] recently synthesized an ABC 3-miktoarm star terpolymer having arms of PS, PI, and PMMA using the approach shown in Scheme 84. After purification this polymer exhibited 1= 1.13 as measured by SEC. Unfortunately no absolute characterization was performed. 

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. 

Architectural polymers (Hirao etal, 2005 Hadjichristidis etai, 2006) refer, in this chapter, to polymers that have finite molecular weights and are architecturally more complex than linear chains. They can be cyclic, star-shaped, combed, balloon-shaped, and H-shaped. Illustrated in Figure 24.1 are the structures of cyclic, balloon-shaped, and H-shaped polymers, as well as of a miktoarm star ABC triblock copolymer. 

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