Living linking reactions

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]. 

It was found that there was a major effect of solvent on this cyclization reaction involving the reaction of a,0)-dilithiumpolystyrene with MDDPE (73). In THE at -20 °C, the linear fraction was estimated to comprise 36-63% of the product mixture. However, when the cyclization reaction was effected in cyclohexane, only 2-3% linear contaminants were observed. This is consistent with previous studies of living linking reactions which showed that the reaction of two moles of poly(styryl)lithium with MDDPE produced only 19% dimer in THE, while the yield of dimer was essentially quantitative (>98%) in cyclohexane or benzene [197, 205]. 

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

The method takes advantage of the steric hindrance of the polystyryllithium living end, which in combination with the excess silane used for the linking reaction, reduces the possibility for the formation of the coupled byproduct. The reaction sequence was monitored by SEC and the reaction products were characterized by MO, differential laser refractometry and LALLS, revealing that well defined polymers were prepared. 

The third method is based on a polymer-linking reaction where the liner polymers are obtained by the living radical polymerization with divinyl compounds. This can afford star polymers with a relatively large number of arms, up to several hundred per molecule, while the number of arms by definition involves a statistical distribution in a single sample. 

The most general and useful method for the synthesis of star polymers by anionic polymerization is the linking reaction of the living polymers with a suitable electrophilic reagent. Several linking agents have been used for the synthesis of star polymers.7 The most important of those are the chlorosilanes28 and the chloromethyl or bromomethyl benzene derivatives.2930... 

The linking reactions of living polymers with the chlorosilanes proceed without any side reactions. However, the efficiency of the linking reaction de-... 

The two remaining Si—Cl bonds of the methyldichlorosilane end-capped PSa arm were then reacted with a small excess of living PSeLi chains. The PSBLi chains were end-capped with a few units of butadiene to facilitate the completion of the linking reaction. 

DPE-functionalized macromonomers were also used for linking reactions with living polymeric anions,... 

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