Step‐growth Polymerization of Aziridines with Elemental Sulfur: Easy Access to Linear Polysulfides and Their Use as Recyclable Adhesives

Abstract

The bulk radical polymerization of bis(aziridine) with molten elemental sulfur resulted in brittle, cross‐linked polymers. However, when the bis(aziridine) was treated with elemental sulfur in the presence of an organobase, the ring‐opening reaction of aziridine with oligosulfide anions occurred, leading to the formation of linear polymers by step‐growth polymerization. These newly synthesized polymers possess repeating units containing a sulfonamide or amide functional moiety and oligosulfide bonds with an average sulfur segment of about two. A small molecular model reaction confirmed the nucleophilic addition reaction of elemental sulfur to aziridine. It was verified that S–S dynamic bond exchange takes place in the presence of an organic base within the linear chains. The mixture of the synthesized polysulfides with pyridine exhibits exceptional adhesive properties when applied to steel, and aluminum substrates. Notably, these prepared adhesives displayed good reusability due to the dynamic S‐S exchange and complete recyclability due to their solution processability. This elemental sulfur‐involved polymerization approach represents an innovative method for the synthesis of advanced sulfur‐containing polymers, demonstrating the potential for various applications in adhesives and beyond.

Aziridine-Derived Polysulfide Elastomers for Self-Healable, Strong, and Reusable Adhesives

“…Very recently, we found that N-tosyl aziridine can undergo a radical ring-opening reaction with molten elemental sulfur but with no regioselectivity. 45 The inverse vulcanization of bis(N-sulfonyl aziridine) gave brittle polymers with poor mechanical properties. Despite the unsuccess of producing high-performance polymers, the high reactivity of the aziridine may contribute to the incorporation of functional moieties into the polysulfide materials.…”

“…Very recently, we found that N -tosyl aziridine can undergo a radical ring-opening reaction with molten elemental sulfur but with no regioselectivity . The inverse vulcanization of bis­( N -sulfonyl aziridine) gave brittle polymers with poor mechanical properties.…”

“…While several adhesive examples exist, they often necessitate prolonged curing times and elevated temperatures (160 °C for 24 h). , The creation of latent adhesives can also be achieved by blending polysulfide with pyridine, as pyridine catalyzes the metathesis of the dynamic covalent S–S bond . We recently synthesized linear polysulfides by the copolymerization of bisaziridine with elemental sulfur for reusable adhesives . However, one drawback of this kind of adhesive is the use of the hazardous Bu 3 P as a catalyst.…”

“…44 We recently synthesized linear polysulfides by the copolymerization of bisaziridine with elemental sulfur for reusable adhesives. 45 However, one drawback of this kind of adhesive is the use of the hazardous Bu 3 P as a catalyst. Hence, the imperative goal is to develop polysulfide adhesives with rapid bonding and environmental friendliness.…”