Thiol-ene Reactions for Monomer Synthesis

The first publication on the thiol-ene reaction of a vegetable-oil derivative dates to 1957, when Koenig and Swern published the free-radical addition of mercaptoacetic acid to oleic acid, methyl oleate, methyl ricinoleate and 10-undecenoic acid. That is, the synthesis of derivatives of a,(0-dicarboxylic oleic acid through thiol-ene addition [6]. 

The studies described here are intended to illustrate the state-of-the-art of this strategy. The works that followed this pioneering study, despite being of great importance and the foundation for other studies, are purposely omitted in this chapter. 

The research team of Cramail adopted a similar strategy to prepare aliphatic diols containing monoester, diester, ester-amide, monoamide and diamide linkages from methyl 10-undecenoate derivatives [15]. Resulting diols were condensed with a methyl diester, obtained by the self-metathesis of methyl 10-undecenoate, in the presence of TBD as a transesterification catalyst. This strategy lead to various fully aliphatic polyesters and polyester-amides with Mn values of 6-19 kDa, a glass transition temperature (Tg) below room temperature (RT) and T of 22-127 °C. 

Another recent study on polyester synthesis through thiol-ene reactions for preparation of monomers from fatty-acid derivatives was described by Pang and co-workers [16]. Authors adopted the same approach for preparing aliphatic diols and diester from 10-undecen-l-ol, methyl 10-undecenoate and thiols. In parallel, they prepared aromatic diesters from methyl vanillate and a series of thermoplastic polyesters were synthesised by polycondensation of the diols and diesters using conventional transesterification methods. These materials were obtained with Mn values of 12-27 kDa and T values of -13 to 13 °C. 

Gandini and co-workers described a unique double click strategy related to the preparation of monomers based on vegetable-oil derivatives bearing furan heterocycles appended through thiol-ene click chemistry, and their subsequent polymerisation via the Diels-Alder (DA) polycondensation between furan and maleimide complementary moieties (i.e., a second type of click chemistry). Details about the DA reaction, its mechanism, applications and the reason why it is classified as a click reaction can be found in Chapter 7. 

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