Broadband dielectric relaxation spectroscopy of functionalized biobased castor oil copolymer thermosets

Novel biorenewable copolymer thermosets are successfully synthesized by the ring-opening metathesis polymerization (ROMP) of norbornenyl-functionalized castor oil (NCO) and norbornenyl-functionalized castor oil alcohol (NCA) with controlled amounts of 0.8 and 1.8 norbornene rings per fatty acid chain, respectively. The NCO and NCA monomers are mixed in different concentrations and simultaneously polymerized via ROMP using Grubbs catalyst. Broadband dielectric relaxation spectroscopy (BDRS) is used to investigate the molecular dynamics of the fully cured copolymer thermosets over a wide range of frequencies (5 × 10^-2 to 0.5 × 10⁷ Hz) at different constant temperatures (-70 to 125 °C). Four phenomena, namely α-, β-, and γ-relaxation processes and ionic conductivity are observed for all the measured samples. The broadband dielectric relaxation spectroscopy for biorenewable functionalized castor-oil-based copolymer thermosets is presented over a wide range of frequency and temperature. The temperature dependence of the characteristic relaxation times is described by the Vogel-Fulcher-Tammann equation for the α-relaxation process. In the low-temperature range, two separate local relaxation processes, β and γ, are clearly seen and are well described by the Havriliak-Negami equation.