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 degrees C), while melting temperatures ranged from 121 to 170 degrees 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.