Fig. 1. Structural diagram of poly-isoprene molecule and simplified vulcanization structure

Fig. 2. Dielectric constant curves of unaged rubber sample

Fig. 3. Partially aged samples

Fig. 4. Terahertz dielectric constant curves during thermal oxygen aging of samples. (a)Real part; (b) imaginary part

Fig. 5. Dielectric constant curves at 1.0THz frequency point. (a) Real and imaginary parts of dielectric constant versus aging time; (b) average slope of real part curve of dielectric constant versus aging time

Fig. 6. Fitted imaginary parts of dielectric constants

Fig. 7. Distribution of resonant frequency points obtained by fitting

Fig. 8. Real part of dielectric constant at zero frequency, real part of dielectric constant at optical frequency, and dielectric strength