Synthesis of Non‐Isocyanate Poly(Sulfide Urethane) Adhesives by Thermally Initiated Thiol‐Ene Polymerization

Three synthetic routes, thermally initiated thiol-ene polyaddition, isocyanate-based polyaddition, and transurethanization, were compared for the synthesis of non-isocyanate poly(urethane)s (NIPUs). Relatively high molecular weight polymers (Mn up to 19 kg×mol$^{−1}$) were successfully achieved via thiol-ene coupling using α,ω-diene-functionalized carbamates and aliphatic dithiols as monomers under solvent-free conditions and dicumyl peroxide as a thermal initiator at a [SH]/[Ene] ratio of 1.05. Compared to conventional isocyanate and transurethanization methods, the thiol-ene approach demonstrated slightly higher molar mass and reduced formation of urea and carbonate byproducts, independent of the formulation prepared. Thermal and mechanical characterization revealed that NIPUs, especially the ones prepared via thiol-ene, exhibited thermal transitions, tensile strength, and elongation at break comparable to or superior to those of their isocyanate-based counterparts. Adhesive performance was further enhanced through a thermally activated thiol-ene reactive bonding strategy, where in situ polymerization at the substrate interface led to a fourfold increase in lap shear strength (8 MPa) compared to a thermoplastic hot-melt application (2 MPa). ... mehrThese findings highlight that thermally initiated thiol-ene polyaddition is promising for the synthesis of high-performance, isocyanate-free polyurethane materials with potential applications in coatings, adhesives, and thermoplastics.