Constructing Novel High-Performance Dipolar Glass Polymer Dielectrics by Polar Rigid/Flexible Side Chains

Developing new polymer dielectrics with superior dielectric and energy storage properties is urgent to meet the demand for electronic devices in the field of microminiaturization or harsh environments. In this paper, two dipolar glass polymers based on polynorbornene main chain and flexible/rigid cyano side chain were synthesized by ring opening metathesis polymerization method: polymer PCEMT with flexible side chains and polymer PCPMT with rigid side chains. The backbone is built from two rigid five-membered rings, which not only avoids the narrow band gap caused by π-π conjugation of traditional aromatic main chains, but also maintains high thermal stability and high glass transition temperature (T_g). The introduced polar cyano groups on the side chain gave high dielectric constants (ε_r) for both polymers, where the ε_r of PCEMT and PCPMT reached 7.9 and 4.6 at room temperature and 1 kHz, respectively. Due to high polarization and high breakdown strength, the PCPMT obtains a maximum discharge energy density (U_d) of 4.47 J/cm³ at room temperature, which is 1.61 and 1.57 times of biaxially oriented polypropylene and polyimide (Kapton). The supernal T_g of 229 °C makes the energy storage performance of PCPMT almost unaffected at 100 °C. The charge-discharge efficiency (η) always keeps over 90% and an U_d of 5.2 J/cm³ at 480 MV/m is achieved, which is much better than Kapton (U_d = 1.77 J/cm³, η = 42.5%) under the same conditions. This work provides a new idea for preparing the high-performance polymer dielectrics via introducing rigid polar side chains.