Synthesis of Isohexide Diyne Polymers and Hydrogenation to Their Saturated Polyethers.

Abstract

The incorporation of renewable feedstocks into polymer backbones is of great importance in modern polymer science. We report the synthesis of 1,3-diyne polymers derived from the bispropargyl ethers of isosorbide, isomannide, and isoidide. The dialkyne monomers can be polymerized through an adaptation of the Glaser-Hay coupling using a nickel(II) cocatalyst. These well-defined diyne polymers bear an iodoalkyne end group, afforded through an unanticipated reductive elimination pathway, and display glass transition temperatures (Tg) from 55 to 64 °C. Fully saturated, analogous polyethers can be prepared from the hydrogenation of the diyne polymers, and these show Tg values between -10 and -2 °C. Both the 1,3-diyne polymers and the saturated analogues display similar trends in their Tg values vis-à-vis the stereochemical features of the isohexide unit within the backbone. This polymerization provided access to two series of isohexide-based polyethers, the thermal properties of which are influenced by the nature of the 2,4-hexadiynyl and hexamethylene linkers as well as the relative configuration of the bicyclic subunit in the backbone. The reported method represents an important step toward accessing well-defined polyethers from renewable feedstocks using readily available catalysts and convenient ambient conditions.