The molecular weight of the complex is analyzed by MS in ESI positive ion mode and found to be 689.05 Da, confirming the ratio between Cu 2+ and pyridyl imine ligand is 1 : 2 (Figure ). A series of Cu(OTf) 2 coordinated PDMS with different salt concentrations is synthesized (Cu(OTf ) 2 0.2 to Cu(OTf ) 2 , the number in the sample name indicates the mole ratio of PDMS:Cu(OTf) 2 = 1 : n for formulations that deviate from 1 : 1). We expect that Cu 2+ forms a stronger and more stable complex than Li + , yielding a less dynamic network, which can be characterized by the rheology of the PDMS complexes. The linear viscoelastic (LVE) region of each material is first determined by running a strain sweep at a frequency of 1 Hz (Figure ), which shows that the critical strain of Cu(OTf ) 2 is near 1%. An oscillation strain of 0.1% is therefore chosen to perform the frequency sweep for all the samples (Figure ). We first compare the coordination strength of Li + and Cu 2+ by examining the rheological curves of LiOTf and Cu(OTf ) 2 : the storage and loss moduli (G ′ and G ′′ , respectively) of Cu(OTf ) 2 are orders of magnitude higher than the moduli of LiOTf 2 within the full frequency range measured. In Cu(OTf ) 2 , G ′ > G ′′ and G ′ remains independent of the frequency, indicating that the material is in the rubbery plateau region due to the presence of strong metal-ligand coordination, which act as transient crosslinks in the polymer;