Electrochimica Acta, Vol.40, No.13-14, 2239-2244, 1995
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)(2)-PPG4000 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 120K 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 similar to 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 : eta(s) = G(infinity) tau(s). The values of eta(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.