Star-branched polymers heteroarm

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]. 

Quirk RP, Yoo T, Lee BJ (1994) Anionic synthesis of heteroarm, star-branched polymers -scope and limitations. J Macromol Sci Pure Appl Chem A31 911-926... 

The use of bis( 1,1-diphenylethylenes) and tris( 1,1-diphenylethylenes) as living linking agents to prepare heteroarm (miktoarm) star-branched polymers... 

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... 

Polymeric organolithium compounds react simply and quantitatively with 1,1-diphenylethylenes [3, 109]. These reactions have provided a new methodology for the synthesis of star-branched polymers, internally-functionalized polymer chains and stars, as well as heteroarm, star-branched polymers via living linking reactions as shown in Scheme 33 [3, 202, 203, 207]. 

In addition, 1,1-diphenylalkyllithium sites in the living linked polymer product (100) can initiate polymerization of a second monomer (M ) to generate a heteroarm (or mikto-arm), star-branched polymer, 102 [243, 244). 

In order to investigate the best conditions for synthesis of heteroarm star-branched polymers using MDDPE, the preparation of four-armed, star-branched polystyrenes was examined in detail as illustrated in Scheme 34 [203, 207]. 

In order to promote the efficient crossover reaction of the coupled product, 104, with butadiene monomer, the addition of lithium alkoxide (lithium sec-butoxide [LiOR]/[RLi]=1.0) was found to be useful analogous to the effect of lithium alkoxide with the dilithium initiator, 90 [88]. In the presence of lithium sec-butoxide, well-defined, monomodal, heteroarm, star-branched polymers (107) were obtained with high 1,4-microstructure of the polybutadiene blocks [203]. In the absence of the lithium alkoxide, bimodal molecular weight distribution polymers were obtained and residual UV absorption corresponding to the diphenylalkyllithium initiator groups at 438 nm was still observed after all of the monomer had been consumed. 

Hayashi, M., Negishi, Y., and Hirao, A. (1999b) Synthesis of heteroarm star-branched polymers by means of anionic living polymerization in conjunction with functional group transformation. Proceedings of the Japan Academy, Series B, 75,93-96. 

Hirao, A., Hayashi, M., and Matsuo, A. (2002c) Synthesis of branched polymers by means of living anionic polymerisation. 10. Synthesis of well-defined heteroarm star-branched polymers by coupling reaction of chain-functionalized polystyrenes with benzyl halide moieties with Uving anionic polymers of tert-butyl methacrylate. Polymer, 43,7125-7131. 

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. 

Heteroarm Star-Branched Polymers by Living Linking Reactions with DVB... 

This review covered recent developments in the synthesis of branched (star, comb, graft, and hyperbranched) polymers by cationic polymerization. It should be noted that although current examples in some areas may be limited, the general synthetic strategies presented could be extended to other monomers, initiating systems etc. Particularly promising areas to obtain materials formerly unavailable by conventional techniques are heteroarm star-block copolymers and hyperbranched polymers. Even without further examples the number and variety of well-defined branched polymers obtained by cationic polymerization should convince the reader that cationic polymerization has become one of the most important methods in branched polymer synthesis in terms of scope, versatility, and utility. 

Miktoarm star (or p-star) polymers are star polymers with branches of different polymers. These polymers are also called heteroarm or mixed-arm star polymers. Their synthesis is more difficult but success has been achieved by sequential coupling [Hadjichristidis, et al., 1999]. To obtain a 3-arm star with one polyisoprenyl (PI) and two polystyryl (PS) branches, polyisoprenyllithium is reacted with an excess of CH3SiCl3 to form the one-arm polymer, the unreacted CH3SiCl3 is removed, and then polystyryllithium is added ... 

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