No abstract

Cobalt(II)-pyridinedicarboxamide-co-polydimethylsiloxane (Co-Py-PDMSs) and cobalt(II)-bipyridinedicarboxamide-co-polydimethylsiloxane (Co-Bipy-PDMSs) polymer−metal complexes were prepared by complexation between Py-PDMSs or Bipy-PDMSs ligands and cobalt(II); the metal content in these complexes varied from 0.09 to 2.41 wt %. The Co II binding patterns (the Co−N Py and Co−O coordination in Co-Py-PDMSs and Co−N Bipy in Co-Bipy-PDMSs) were established by UV−vis and IR methods and by comparison with model Co II complexes exhibiting relevant O,N,O-and N,N-coordination environments, respectively. The mechanical properties of the polymer−metal complexes were controlled by the coordination of Py-PDMSs or Bipy-PDMSs to Co II at various metal-toligand molar ratios (1:(1−6)) and by the variation of the polydimethylsiloxane unit length (M n : 850−900, 5000, or 25 000 g•mol −1 ). Utilization of the chelated Py-PDMSs and Bipy-PDMSs polymer ligands, which are capable of tri-or bidentate binding of Co II , led to (2−4)-fold increases in tensile strength (up to 1.75 MPa) and much higher elongation at break ((2−3)-fold increase up to 2100%) compared with the previously reported Co II -based polymer− ligand systems featuring monodentate ligation entities. Changing the main-chain ligand from Py-PDMSs to Bipy-PDMSs led to an increase in tensile strength of (2−4)-fold in comparison with Py-PDMS and a lower hysteresis (4%). The room temperature selfhealing efficiency was up to 96% for Co-Py-PDMSs and 40% for Co-Bipy-PDMSs, as measured for a polydimethylsiloxane unit with M n = 25 000 g•mol −1 .