Rubbery behavior from low molecular weight polymers using high field cation endlinkers

We describe a simple approach to making rubbery thermoplastic materials starting with low molecular weight polymers and using a ion/dipole linkages between the chain ends. We observe thermoplastic behavior in the system Mg(ClO₄)₂PPG4000 in the composition range 2-7mol.% Mg(ClO₄)₂. Shear modulus measurements reveal a rubber-like shear modulus above the glass transition temperature which is characteristic of high molecular weight polymers. The temperature at which the shear viscosity relaxation time reaches 100s normally associated with the glass transition lies 120 K above the DSC T_g which itself remains close to the value of the pure polymer as salt content is increased but shows a composition-dependent strength. This strength vanishes at ~9% Mg(ClO₄)₂ and more Mg(ClO₄)₂-rich solutions are then brittle glasses at ambient temperature. Shear modulus relaxation measurements and shear viscosity data yield concordant results when related through the Maxwell equation: η_s = G_∞τ_S. The values of η_S can be fitted to the VTF equation but the value of the pre-exponent is more characteristic of ordinary liquids than of high molecular weight polymers, establishing this rubber as one of an unusual type. The thermoplastic behavior is attributed to the thermal rupture of Mg²⁺-to-chain end OH-links which create a network of high effective molecular weight at low temperatures. This behavior is almost unique to perchlorates presumably because of the non-competitive character of ClO₄^- relative to -OH in coordinating the cation.