Extra-Soft Self-Healable Supramolecular Silicone Elastomers from Bis-Amide-PDMS Multiblock Copolymers Prepared by Aza-Michael Reaction

Abstract

Silicone elastomers involving self-associating bis-amide groups were synthesized by aza-Michael addition between N,N′-methylenebis(acrylamide) and low molecular weight bis(3-aminopropyl)-terminated poly(dimethylsiloxane). In mild conditions that favor monoaddition (reaction of a primary amine) over diaddition (reaction of the resulting secondary amine), a library of non-crosslinked copolymers was prepared by tuning the vinyl-to-primary amine reactive function molar ratio. Almost no diadduct was observed for a reactive function molar ratio lower than 0.8, thus leading to linear polymers with predictable molecular weights. On the other hand, diaddition occurs at higher molar ratios such that polymers with some branches, high molecular weights, and large dispersity were synthesized. Regardless of the polymers considered, the amide groups develop some H-bond interactions as demonstrated by FTIR, leading to phase-separated domains, as revealed by DSC, which alters rheological and viscoelastic properties of the polymers. By increasing the molecular weight of the polymers, it was possible to turn the copolymers from viscoelastic liquids to viscoelastic solids and further to elastomers. Moreover, the latter material presents self-healing propensity at room temperature, which may be related to the diffusion of short chains, while the mechanical properties (strain and stress at break) are endowed by the long entangled linear-like chains, properties that are recovered after healing.