The preparation of telechelic oligomers and polymers is of great interest for a number of fields, but it is typically quite difficult to generate compounds such that they are perfectly difunctional (fn = 2.0). However, olefin metathesis has proven to be a versatile method for the synthesis of telechelics. For example, ring-opening metathesis polymerization (ROMP) of cyclooctadiene in the presence of a difunctional chain transfer agent (CTA) is a very successful route to obtain telechelics with functionality of very nearly 2.0 and shows great promise [1].
A different method of using metathesis polymerization to obtain telechelic compounds is by the use of ADMET depolymerization, as reported by the Wagener group [2]. By their method, 1,4-polybutadiene can be depolymerized by well-defined Schrock catalysts when combined with an excess of difunctional alkene CTA such as diethyl-4-octene-1,8-dioate. The functionalized alkene had to be chosen carefully, as placement of the functional groups too close to the olefin may cause them to interfere with the metathesis (either due to electronic effects or chelation of the functional group to the catalyst). Simple variation of the difunctional alkene allowed for the generation of perfectly difunctional ester-, silyl ether-, and imide-terminated polybutadiene oligomers.
References
[1] Morita T, Maughon BR, Bielawski CW, Grubbs RH, “A ring-opening metathesis polymerization (ROMP) approach to carboxyl- and amino-terminated telechelic poly(butadiene)s” Macromolecules 2000, 33, 6621.
[2] Marmo JC, Wagener KB. “ADMET depolymerization. synthesis of perfectly difunctional (f=2.0) telechelic polybutadiene oligomers.” Macromolecules 1995, 28, 2602.
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