Preparation of Dynamic Covalent Polymers via Inverse Vulcanization of Elemental Sulfur

The synthesis of dynamic covalent polymers with controllable amounts of sulfur-sulfur (S-S) bonds in the polymer backbone via inverse vulcanization of elemental sulfur (S8) and 1,3-diisopropenylbenzene (DIB) is reported. An attractive feature of the inverse vulcanization process is the ability to control the number and dynamic nature of S-S bonds in poly(sulfur-random-(1,3-diisopropenylbenzene)) (poly(S-r-DIB) copolymers by simple variation of S8/DIB feed ratios in the copolymerization. S-S bonds in poly(S-r-DIB) copolymers of high sulfur content and sulfur rank were found to be more dynamic upon exposure to either heat, or mechanical stimuli. Interrogation of dynamic S-S bonds was conducted in the solid-state utilizing electron paramagnetic resonance spectroscopy and in situ rheological measurements. Time-dependent rheological property behavior demonstrated a compositional dependence of the healing behavior in the copolymers, with the highest sulfur (80 wt % sulfur) content affording the most rapid dynamic response and recovery of rheological properties.