A rubber sample is investigated by dielectric spectroscopy in the frequency range from ${10}^{-2}<~\nu <~{10}^7\mathrm{Hz}.$ Measurements are performed under both isothermal (at ambient pressure) and isobaric conditions. The spectral shape of the loss peaks is symmetric and temperature and pressure independent. Hence the temperature-pressure-frequency superposition principle is fulfilled in a cross-linked rubber sample. The Vogel-Fulcher-Tammann temperature law and its pressure counterpart well describe the respective temperature and pressure dependences of relaxation times. In addition we determined the activation volume from isothermal relaxation data.

The results presented give the evidence for the quasicritical, pretransitional behavior of dielectric properties in the isotropic phase of a rodlike nematic liquid crystal with the transverse permanent dipole moment. Studies were conducted in 2-cyano-4-pentylbiphenyl 4-(trans-4-pentylcyclohexyl) benzoate, focusing on the static-and ionic-dominated low-frequency (LF) regions. For the static dielectric permittivity [ε′(T)] the application of the derivative analysis revealed the pretransitional anomaly associated with the specific heat exponent α≈0.5. For the LF domain the contribution to ε′(T) from residual ionic impurities follows a linear temperature dependence on approaching the isotropic-nematic (I-N) transition. This dependence and pretransitional anomalies of electric conductivity and dielectric modulus can be associated with the influence of prenematic fluctuations. “Linear” dielectric studies were supported by the static nonlinear dielectric effect measurements, which delivered reliable estimations of the temperature of the hypothetical continuous phase transition T* and the discontinuity of the I-N transition ΔT≈1.7K.