Bio-based thioether polyols from limonene and geraniol: Toward sustainable high-performance polyurethane thermosets

Abstract

Polyurethanes (PUs) are ubiquitous amongst versatile polymeric materials that are usually made by the reaction of polyisocyanates with polyols, yielding materials with a wide range of mechanical, chemical, and physical properties. Nowadays, more attention is given to designing PU networks involving the emerging techniques, including structurally modified bio-based polyols, compared to the use of conventional petroleum-based resources. In this context, “thiol-ene” click reactions are one of the most effective techniques for structural modification of unsaturated bio-based resources to prepare the polyols under a sustainable approach. Herein, we have developed an efficient route for the synthesis of limonene and geraniol-based thioether polyols (LME and GME) via the “thiol-ene” click reaction under solvent-free conditions. Thereafter, the prepared thioether polyols were used to fabricate a series of polyurethane thermoset networks under catalyst-free condition with tunable thermal and mechanical properties involving two different diisocyanates (IPDI and CHMDI) for PU formulation. Additionally, the influence of soybean oil polyol (SBPO) on the structural rigidity of the PU networks has also been investigated. All the PU thermosets appear as transparent, rigid, or semi-rigid films and exhibit a high glass transition temperature (T_g) as well as robust mechanical properties. For instance, all the prepared PU thermosets displayed the tunable T_g values ranging from 20.5 to 75.3 °C, and the highest tensile strength of ∼36 MPa and shore D hardness of ∼85 was achieved for the GME-IPDI polyurethane thermoset. The fabricated PU materials exhibit moderate UV resistance and also no significant yellowing phenomenon was observed due to the presence of aliphatic backbone. Briefly, the present work explores the scope of terpene feedstocks for the development of sulfur-functionalized high-performance polyurethane networks with enhanced thermal stability and mechanical strength.