Macromonomer Synthesis Using Anionic Polymerization Methods

2 Macromonomer Synthesis Using Anionic Polymerization Methods 

Anionic polymerizations, when carried out in aprotic solvents, are characterized by the long lifetime of the carbanionic (or oxanionic) sites l2). When neither spontaneous transfer nor termination reactions are involved, the polymers obtained exhibit sharp molecular weight distributions, and their number average degree of polymerization is determined by the [Monomer]/[Initiator] molar ratio, provided initiation is fast as compared to propagation. However, the major advantage of these methods, as far as synthesis is concerned, is the socalled living character of the polymers 12) After completion of the polymerization the active sites retain their reactivity and can be used for functionalizations at the chain end. 

Two direct pathways can be imagined, to fit a polymer molecule at its chain end with a polymerizable unsaturation. 

Anionic polymerization has also been used as a route to various indirect macromonomer syntheses. Functionalizations are easy to carry out anionically, and the terminal functions thus created can be reacted further, e.g. with unsaturated derivatives. 

All pathways involving anionic polymerization allow in principle an adequate control of the molecular weight and ensure low polydispersities. They often lead to well defined macromonomers. We shall now present the various procedures published in articles and patents and critically appraise the results obtained and the limitations of the methods proposed. 

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Techniques derived from anionic or cationic living polymerization methods have widely been used. They are efficient because of the long lifetime of the active sites. Once polymerization is completed these sites are used for functionalization purposes. Alternately, unsaturated ionic initiators have been used but to a lesser extent because of the requirement involved that the polymerizable groups remain unscathed during the macromonomer formation. The versatile inifer method has also been applied to the synthesis of macromonomers. 

In analogy to anionic polymerization, both initiating and end-capping methods are used to obtain macromonomers via cationic polymerization. However, termination is only quantitative in the case of ring-opening polymerizations. Table 5 presents some representative methods which have been reported for the synthesis of macromonomers from PTHF. Scheme 14 shows a typical reaction scheme in which the end group is introduced using a functionalized initiator. ... 

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