Polar-modified alkyllithium

Antkowiak, A.E., Tate, D.P., Oberster, A.E., et al., 1972. Temperature and concentration effects on polar-modified alkyllithium polymerizations and copolymerizations. J. Polym. Sci. Part A ... 

Microstructure variation in both polybutadiene and polyisoprene polymers has been realized by using alkyllithium initiators in the presence of polar modifiers. 

All of the studies published to date fail to identify the active catalyst species present in the RLi-TMEDA polymerization of ethylene. The kinetics data of both Hay and Shud and their co-workers fall short in this respect. A more fundamental approach is needed. It may be appropriate at this time to study the 13C- and 7Li-NMR of alkyllithium compounds in the presence of various chelating diamines and polar modifiers such as THF and dimethyl ether. 

Polydiene microstructure is also dependent on the ratio of concentrations of monomer to organolithium. This is true for both non-polar and polar media. As catalyst levels are reduced in a non-polar system, cis-l,4-values as high as 86% have been observed in high molecular weight polybutadienes prepared in the absence of any solvents. This compares with 96% cw-l,4-content in similarly prepared polyisoprenes. In the case of high-vinyl BRs (HVBRs) prepared with a polar modifier, such as DIPIP, a decrease in alkyllithium (RLi) concentration at constant ratio of DIPIP/RLi produces smaller amounts of vinyl structure. 

A unique feature of alkyllithium initiation is that it takes place in a homogeneous reaction mixture where there is a complete absence of termination or other side reactions, so that "living polymers" are formed. This fact, along with the ability of polar solvents to modify the reactivity and mode of reaction, has enormous implications for the synthesis of polymers. 

Coupled (star branched) and end-functional PBs are possible using alkyllithium technology because of the presence of a living anion on the chain end. This anion is available for further reactions, which is discussed later. Upon the addition of polar agents (modifiers), such as ethers or amines, the alkyllithium initiators can produce PBs with vinyl contents up to lOO /o. The vinyl content can be controlled by the ratio of... 

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