Linear viscoelastic rheology of moderately entangled telechelic polybutadiene temporary networks

We investigate the time-dependent linear viscoelastic behavior of amine and alkaline metalneutralized carboxy - telechelic 1,4-polybutadiene, and compare it with the acid precursor as well as an ester end-modified version. The ionic groups form aggregates with a aggregate spacing period around 85 Å, containing about 90 chain-ends. Rheological tests highlight the existence of a strongly time-dependent terminal relaxation and an intermediate frequency relaxation, which can be assimilated to a glass transition of the ionic aggregates and their immediate environment. The terminal relaxation time after neutralization with alkali metal increases by up to 7 decades. Contrary to previously published results, this time is found to be a strongly increasing function of metal atomic mass for the equilibrated structures. The discrepancy can be rationalized by analyzing the annealing time dependence of the phenomena. Earlier studies did not report on truly equilibrated systems. While the main phase glass transition is hardly affected by neutralization, the temporary network formed by the ionic associations shows a very high and ion-dependent temperature sensitivity. Moreover, a failure of the time - temperature superposition principle is found at intermediate temperatures or frequencies, because the terminal and intermediate frequency relaxations do not follow the same temperature dependence.