A Better Monomer Makes Superior Silicones: Synthesis, Mechanical Properties, and Recyclability of Low Defect Hemisilicone Elastomers

The synthesis, mechanical properties, and recyclability of a novel class of elastomers composed of a hemisilicone polymer, −(SiMe₂–O–SiMe₂–CH₂CH₂)_n– (PM₂E), derived from the anionic ring-opening polymerization of 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (c-M₂E), are reported. The lower reactivity of the PM₂E backbone toward nucleophiles/bases, compared to conventional silicones, prevents undesired backbiting and chain transfer side reactions, facilitating the formation of low defect hemisilicone elastomers. These elastomers exhibit exceptional mechanical properties, with elongation exceeding 1000% without fracture, as well as minimal hysteresis under 500% strain. The tear resistance is similarly outstanding, as no crack propagation occurs from initial notches during elongation. In terms of recyclability, a base-catalyzed degradation process effectively cleaves the cross-linking junctures, yielding a liquid polymer with >97% efficiency. Subsequent distillation in the presence of KOH, followed by standard redistillation, regenerates the pure monomer in >70% yield based on the elastomer mass. The combination of superior mechanical performance and efficient recyclability highlights hemisilicone elastomers as promising, sustainable, and superior (in some respects) alternatives to conventional silicone elastomers.