Renewable polyamides via thiol-ene ‘click’ chemistry and long-chain aliphatic segments

Thiol-ene ‘click’ chemistry was utilised to prepare dicarboxylic acid monomers containing two sulphur units within the backbone, which subsequently underwent polycondensation to yield a series of renewable, long-chain, fatty-acid derived linear polyamides. The linear sulphur-containing polyamides displayed number-average molecular weights of 8000–55,000 g·mol⁻¹ and broad polydispersities biased towards higher weight fractions. Glass transition values were slightly above room temperature (31–35 °C), while melting temperatures ranged from 121 to 170 °C. This novel class of polymers exhibited an impressive property profile, most notably exceptional impact resistance, tear strength, high elasticity, very low water absorption yet high oxygen- and water vapour permeability. The presence of sulphur and the increased aliphatic segment length influenced a wide spectrum of polyamide properties due to the reduced amide linkage (and inter-chain hydrogen bonding) density and less-effective chain packing ability due to the increased atomic radii of the sulphur atoms. The data highlights the technical advantages of these polymers, while also expanding the repertoire and structure-property relationships of both long-chain- and sulphur-containing polyamides, and encouraging further development of polyamide derivatives from renewable sources.