Dynamics of Poly(methyl methacrylate) in Ionic Liquids with Different Concentration and Cationic Structures

The dynamic behavior of entangled poly(methyl methacrylate) (PMMA) chains in both the traditional monocationic ionic liquid (MIL) and synthetic dicationic ionic liquid (DIL) with the same anion bis[(trifluoromethyl)sulfonyl]imide ([TFSI](-)) has been examined over the wide composition range using differential scanning calorimetry and rheological measurements. PMMA/DIL and PMMA/MIL systems exhibit two glass transitions in the midrange of composition due to self-concentration effects. PMMA in DIL shows slower relaxation behavior, however, after the iso-free-volume correction, the terminal relaxation time tau(0) of PMMA in both the DIL and MIL presents the power law behavior tau(0)similar to phi(v) with exponent v conforming to experimental results for conventional polymer solutions (v=2.0 +/- 0.2). At high ILs concentration (70%), the entanglement molecular weight M-e of PMMA/DIL system is lower than that of PMMA/MIL system owing to the formation of additional physical network in DIL, while the difference of M-e is reversed at low ILs content. The composition dependence might be related to the fact that the probability of formation of physical cross-linking points in linked double imidazolium ring increases with the increase of DIL content. The recovered creep strain of PMMA/DIL is almost 18 times of PMMA/MIL, exhibiting significantly better viscoelastic behavior.