We study the slow relaxation of stress in polydomain acrylate liquid crystalline elastomers undergoing the alignment transition under an imposed extension. We analyse the long-time stress relaxation, the slow approach to the mechanical equilibrium and the role of time-temperature superposition. By building the master curves, we investigate extrapolated time intervals and show the presence of two distinct relaxation regimes. At the first stage, the fast power-law relaxation of stress, with the exponent 0.67, means that directional changes in nematic domains are dominant. At very long times, we find that a different, slow power law (with the exponent 0.15) becomes the dominant mode, similar to the classical results in isotropic rubbers. Model equilibrium stress-strain curves have been obtained by extrapolating the master curves. It appears that, at a true mechanical equilibrium, one finds no mesogenic effects in stress-strain, meaning that the non-trivial nematic effects could be transient, locked by network entanglements, but capable of completely relaxing by (very slow) rearrangement of network chains.
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