Synthesis of Aldehyde Functional Polydimethylsiloxane as a New Precursor for Aliphatic Imine-Based Self-Healing PDMS

The development of a simple synthetic route to aldehyde functional poly(dimethylsiloxane) (PDMS) through oxidative C─C bond cleavage of terminal epoxide functions by periodic acid is presented first. Nuclear Magnetic Resonance (NMR) and Infrared spectroscopies revealed the full conversion of the PDMS terminal epoxides to aldehyde groups. This new aldehyde functional PDMS is then used to elaborate aliphatic self-healing materials through imine chemistry by reaction with an amine-terminated PDMS featuring urea moieties in its structure. The reactivity of the aldehyde terminated PDMS is investigated through the preparation of supramolecular networks formed by the hydrogen bonds of ureas. The incorporation of permanent chemical cross-linking points through reaction with a triisocyanate leads to the preparation of covalent adaptable networks (CANs). As a result, materials with a wide range of mechanical properties are obtained, depending on the composition and structure of the PDMS networks. Due to the presence of dynamic covalent imine bonds, the supramolecular networks show excellent scratch recovery at room temperature while the CANs retain their mechanical properties after two cycles of reshaping by heating.