Solid polymer electrolytes. IV. Preparation and characterization of novel crosslinked epoxy-siloxane polymer complexes as polymer electrolytes

Two series of novel crosslinked siloxane-based polymers and their complexes with lithium perchlorate (LiClO₄) were prepared and characterized by Fourier transform infrared spectroscopy, solid-state NMR (¹³C, ²⁹Si, and ⁷Li nuclei), and differential scanning calorimetry. Their thermal stability and ionic conductivity of these complexes were also investigated by thermogravimetric and AC impedance measurements. In these polymer networks, poly(propylene oxide) chains with different molecular weights were introduced through self-synthesized epoxy-siloxane precursors cured with two curing agents. The glass-transition temperature (T_g) of these copolymers is dependent on the length of the ether units. The dissolution of LiClO₄ considerably increases the T_g of the polyether segments. The dependence of the ionic conductivity was investigated as a function of temperature, LiClO₄ concentration, and the molecular weight of the polyether segments. The ion-transport behavior was affected by the combination of the ionic mobility and number of carrier ions. The ⁷Li solid-state NMR line shapes of these polymer complexes suggest a significant interaction between Li⁺ ions and the polymer matrix, and temperature- and LiClO₄ concentration-dependent chemical shifts are correlated with ionic conductivity.