Viscoelastic Properties of Water-Absorbed Poly(methyl methacrylate) Doped with Lithium Salts with Various Anions

We investigated the effects of water absorption on the dynamic mechanical properties of poly(methyl methacrylate) doped with various generic lithium salts, such as lithium perchlorate trihydrate (LiClO₄), lithium trifluoromethanesulfonate (LiCF₃SO₃), lithium nonafluorobutanesulfonate (LiC₄F₉SO₃), and lithium bis(trifluoromethanesulfonyl)imide (LiN(CF₃SO₂)). The rates of weight change during water absorption of lithium salt-doped samples were higher in the following order: LiClO₄, LiCF₃SO₃, LiC₄F₉SO₃, and LiN(CF₃SO₂). Interestingly, the aforementioned order was the same as the order of the terminal relaxation times in the flow region of the viscoelastic measurement in the melting-state. This implies that the water absorption of the salt-doped PMMA occurs due to the factors that affect the pinning of the PMMA molecular chains in the places.