Nickel(II)-pyridinedicarboxamide-co-polydimethylsiloxane complexes as elastic self-healing silicone materials with reversible coordination

The nickel(II)-pyridinedicarboxamide-co-polydimethylsiloxane complexes as elastic silicone rubbers were prepared. The structure of the Ni(II) coordination cross-links was fully characterized by X-ray crystallography, high-resolution mass spectrometry, IR and UV–vis spectroscopy of the low-molecular weight model complex. The nickel content in the polymer-metal complexes varied from 2.78 to 0.12 wt%. Mechanical properties of the polymer-metal complexes was controlled by the Ni(II) load variations, metal to ligand molar ratios of 1:(1–8), and by the polydimethylsiloxane unit length, Mn: 850–900, 5000 or 25000 g∙mol−1; an increase of the polysiloxane chain length and a decrease of Ni(II) load led to higher elasticity and lower hysteresis (3%). The elongation at break of the polymer-metal complexes was up to 1800% and the self-healing efficiency was up to 92.5% at room temperature (for the rubber with a polydimethylsiloxane unit Mn = 25000 g∙mol−1). The glass transition temperatures of the nickel(II)-pyridinedicarboxamide-co-polydimethylsiloxanes were from −123 °C to −112 °C, and the electroconductivity was 10−13–10−11 S∙cm−1.