whereas in LiOTf, G ′ < G ′′ , indicating that the material is in the terminal region, where chains relax quickly and the material behaves like a viscoelastic fluid. The difference in viscoelasticity of the Li + and Cu 2+ coordinated PDMS can also be directly seen from the photos of LiOTf and Cu(OTf ) 2 samples: the former is a viscous liquid and the later is a flexible film, confirming that Cu 2+ yields much stronger bonding with the ligand functionalized PDMS than Li + . The variation of polymer viscoelasticity of the Cu 2+ -coordinated PDMS as a function of Cu(OTf) 2 concentration is also shown in the rheology plot: the material transforms from a viscoelastic fluid to a viscoelastic solid with increasing Cu(OTf) 2 concentration. A crossover between the storage and loss modulus arises and shifts to the lower frequency at the higher Cu(OTf) 2 concentration, indicating that the characteristic relaxation time of the PDMS is significantly prolonged when it is crosslinked by Cu(OTf) 2 . The change in polymer dynamics caused by using the more strongly coordinated Cu 2+ or increasing the Cu salt concentration also results in the increase of T g , which is measured by differential scanning calorimetry (DSC) (Figure ). The T g of LiOTf, Cu(OTf ) 2 0.2, and Cu(OTf ) 2 0.4 is below the testing limit of the machine (-90 ℃), so no slope change is seen on the heat flow curve. However, the T g of Cu(OTf ) 2 0.6, Cu(OTf ) 2 0.8, and Cu(OTf ) 2 increases to around -38 ℃, -30 ℃, and -28 ℃, respectively. The dramatic increase in T g reflects the reduction of chain mobility, which should confine the ion transport. To study how the coupled Cu 2+ ion concentration and network dynamics together effect the ionic conductivity of the material, we measure the ionic conductivity of the PDMS complex as a function of Cu(OTf) 2 concentration, showing quite a different trend than in the Li + coordinated system (Figure ). We note that the Cu(OTf) 2 coordinated PDMS, regardless of salt concentration, cannot achieve nearly as high conductivity as the maximum value of the LiOTf coordinated PDMS. The maximum ionic conductivity is obtained at Cu(OTf ) 2 0.4, which is far lower than the maximum coordination capacity. In addition, a drastic decrease of the ionic conductivity is observed beyond this peak. This trend can be well correlated to the change in the rheological behavior and the glass transition temperature with increasing Cu(OTf) 2 concentration. At low Cu(OTf) 2 concentrations, the PDMS complex is still fluid and its glass transition temperature is far below the room temperature (T > T g +100 ℃), so the fast chain segmental motion facilities the ion motion at room temperature, which is similar to the Li + coordinated system. Increasing Cu(OTf) 2 concentration from Cu(OTf ) 2 0.2 to Cu(OTf ) 2 0.4 improves the ion concentration and therefore increases the ionic conductivity of the material. However, the trend is interrupted by the slowing of polymer dynamics in the system at higher Cu(OTf) 2 concentration. For Cu(OTf ) 2 0.6, Cu(OTf ) 2 0.8, and Cu(OTf ) 2 , the ion motion slows down due to the significantly extended chain relaxation. Another interesting observation is that the Cu 2+ system is more ionically conductive than the Li + system at the low salt concentration of PDMS:salt=1 : 0.2 and 1 : 0.4 (Figure ). This can be attributed to the valency of the metal cation: Cu 2+ is balanced by two OTf -anions whereas Li + only has one, so when adding the same number of moles of LiOTf and Cu(OTf) 2 salt into the PDMS, the ion concentration is higher in the Cu 2+ system than the Li + system, which promotes the high ionic conductivity.