Thiol-ene Reactions for Chemical Modifications after Polymerisation

3 Thiol-ene Reactions for Chemical Modifications after Polymerisation 

Post-polymerisation modifications of polymer structures based on the thiol-ene reaction are important tools in macromolecular science because several thiol compounds bearing diverse functional groups can be introduced easily onto a polymer chain that bears non-activated mono-substituted double bonds as functional groups 

Kolb and Meier [43] prepared a malonate derivative of methyl 10-undecenoate, which was polymerised further with 1,6-hexanediol using titanium (IV) isopropoxide as a catalyst. This polymalonate, bearing a C9 aliphatic side chain with terminal double bonds, was then subjected to grafting by ruthenium-catalysed cross-metathesis reactions with acrylates or thiol-ene addition reactions. This functionalisation enabled a subsequent Passerini multi-component reaction [44] using the pendant carboxylic-acid moiety of the modified polymers that resulted from the thiol-ene addition of 3-mercaptopropionic acid into the initial double bonds of the polymer. 

Quantification of the thiol-ene coupling was carried out by H-NMR and revealed, in all cases, reduction of the double-bond peak at =5.4 ppm in the spectra of the final product. This finding suggested that the efficiency of thiol-ene coupling was 75% for the reaction undertaken with the thiol with an internal ester moiety, and 95% for reactions carried out with the aliphatic thiol incorporating an internal amide moiety. Values of molecular weight after functionalisation were 16-26 kDa. 

Cadiz and co-workers [46] prepared telechelic polyester diols through two subsequent thiol-ene reactions. That is, a step growth polymerisation using allyl-lO-undecenoate and 3,6-dioxa-l,8-octanedithiol, followed by end-group post-polymerisation modification with 2-mercaptoethanol. Telechelics based on divinyl monomers are interesting materials with potential applications in the tailoring of polymer structures and properties. 

---