To investigate the effect of coordination strength on the ionic conductivity of the polymer, a series of Cu 2+ coordinated PDMS with different salt concentration is synthesized. From the rheological measurements, we show that as expected, Cu 2+ forms a much stronger coordination with the ligand on the PDMS than Li + . The Cu 2+ coordinated PDMS transforms from a viscoelastic fluid to an elastic solid as the salt concentration increases, accompanied by a significant rise of T g , indicating a rapid decrease of polymer dynamics. The ionic conductivity of the complex first increases with the Cu(OTf) 2 concentration, but soon reaches the maximum at a low coordination ratio. Further increasing Cu(OTf) 2 concentration leads to a sharp decrease in ionic conductivity. We attribute this to the reduction of chain mobility in the system, which limits the ion transport. In addition, at the same low salt concentration, Cu 2+ coordinated PDMS exhibits higher ionic conductivity than Li + coordinated PDMS due to the doubled concentration of mobile anions. This importance of reduced chain mobility is in contrast to its minor role in the Li + coordinated material. Based on these findings, an optimized metal-ligand coordinated PDMS with higher ionic conductivity and improved mechanical strength is achieved by a combination of high Li + and low Cu 2+ concentration in the system. This paper explores the structure-property relationship of the metal-ligand coordinated PDMS as a novel polymer electrolyte. At a superficial level the governing mechanisms are similar to other polymer electrolytes -salt solvation, chain mobility, ion clustering, ion diffusion, and ion hopping -however, their relative importance and how they are controlled by the polymer structure and salt selection are quite distinct. These insights will enable more strategic future material design of low T g ionically conductive polymers.