Anionic polymerization star-branched polymers

From a practical point of view, the effective molecular weight distribution of an anionically prepared polymer can be broadened by reaction with less than a stoichiometric amount of a linking agent such as silicon tetrachloride [239]. This results in a product mixture composed of unlinked arm, coupled product, three-arm, and four-arm star-branched polymers. Heteroarm star-branched polymers can be formed by coupling of a mixture of polymeric organolithium chains that have different compositions and molecular weights. This mixture can be produced by the sequential addition of initiator as well as monomers [3, 259, 260]. 

A variety of three-arm ABC star-branched polymers can also be synthesized via an addition reaction of a living anionic polymer to a chain-end-DPE-functionalized polymer, followed by the polymerization of an additional monomer (Scheme 5.26) [238, 242-244]. A four-arm ABCD star composed of PS, PaMS, PtBMA, and P2VP, could be synthesized by a similar methodology using l,4-bis(l-phenylethenyl)benzene [245]. Since 2000, two more four-arm ABCD stars have been synthesized using a new method that combines the above-described SiCl and BnX methodologies [246, 247]. 

HIR Hirao, A., Inushima, R., Nakayama, T., Watanabe, T., Yoo, H.-S., Ishizone, T., Sugiyama, K., Kakuchi, T., Carlotti, S., and Deffieux, A., Precise synthesis of thermo-responsive and water-soluble star-branched polymers and star block copolymers by living anionic polymerization, Eur. Polym. J., 47, 713, 2011. 

Higashihara T, Hayashi M, Hirao A. Synthesis of weU-deflned star branched polymers by stepwise iterative methodology using Uving anionic polymerization. Prog Polym Sci. 2011 36 323-75. 

Hirao, A., Hayashi, M. and Haraguchi, N. (2000) Synthesis of well-defined functionalized polymers and star branched polymers by means of living anionic polymerization using specially designed 1,1-diphenylethylene derivatives. Macromol. Rapid Commun., 21,1171-1184. 

Keywords. Anionic polymerization. Living anionic polymerization, 1,1-Diphenylalkyl-lithiums. Functionalized polymers. Block copolymers. Macromonomers, Star-branched polymers. Dilithium initiators. Trilithium initiators. Multifunctional initiators. Living linking reactions. Heteroarm star polymers, Miktoarm star polymers... 

The advantage of this procedure is that, in essence, any monomer that undergoes living anionic polymerization from a DPE anion can be used. On the other hand, the successive synthesis of star-branched polymers can no longer be continued. 

Hayashi, M., Kojima, K., and Hirao, A. (1999a) Synthesis of star-branched polymers by means of anionic living polymerization coupled with functional group transformation. Macromolecules, 32,2425-2433. 

Higashihara, T. and Hirao, A. (2004) Synthesis of asymmetric star-branched polymers consisting of three or four different segments in composition by means of Uving anionic polymerization with a new dual-functionaUzed 1,1-bis (3-chloromethylphenyl)ethylene. Journal of Polymer Science Part A-Polymer Chemistry, 42,4535-4547. 

Hirao, A. and Higashihara, T. (2002b) Synthesis ofbranched polymers by means of living anionic polymerization. 13. Synthesis of well-defined star-branched polymers via an iterative approach using living anionic polymers. Macromolecules, 35,7238-7245. 

Hirao, A., Inoue, K., and Higashihara, T. (2006a) Successive synthesis of regular and asymmetric star-branched polymers by iterative methodology based on Uving anionic polymerization using functionalized 1,1-diphenylethylene derivatives. Macromolecular Symposia, 240,31-40. 

Hirao, A., Sugiyama, K., Tsunoda, Y. et al. (2(X)6) Precise synthesis of well-defined dendrimer-Uke star-branched polymers by iterative methodology based on living anionic polymerization. Journal of Polymer Science Part A-Polymer Chemistry, 44,6659-6687. 

Basically, intermediate polymeric anions were reacted with l-(3-bromopropyl)-2,2,5,5-tetramethyl-aza-2,5-disilacyclopentane, followed by spontaneous deprotection during workup to prepare well-defined in-chain- or core-functionalized star-branched polymers with primary amine group(s). These functionalized polymers could be used as macroinitiators for the living polymerization of NCAs. The success of those star-polymer syntheses may be derived from the 100% introduction of primary amino groups at the precise position and extremely clean media for NCA polymerization in completely sealed reactors based on the high-vacuum technique. 

Zhao, Y, Higashihara, T., Sugiyama, K., and Hirao, A. (2007) Synthesis of asymmetric star-branched polymers having two polyacetylene arms by means of living anionic polymerization using 1,1-diphenylethylene derivatives. Macromolecules, 40,228—238. 

In the following sections, the general methods for synthesis of regular star-branched polymers and heteroarm star-branched polymers will be described. Specific examples will be shown based on alkyllithium-initiated anionic polymerization. 

Star polymers are the simplest of the branched polymers they represent polymers wherein several linear chains are linked to a single multivalent molecular core 3-arm, 4-arm, and even 12-arm star polymers have been synthesized [43]. Typically, the most efficient process to prepare such polymers is to use a living polymerization, such as anionic polymerization, and terminate the process by a nucleophilic substitution reaction onto a multifunctional core. With the advent of CRPs and the CuAAC reaction, Gao and Matyjaszewski utilized, for the first time, a combination of ATRP and click reaction to prepare star-branched polymers [44] as described earlier, ATRP can be readily used to prepare azide-terminated polystyrene by transforming the terminal bromide, which is typically installed at one chain end during ATRP, to an azide. The PS-azide was then reacted with different core molecules bearing multiple propargyl groups an example is the... 

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