Curing behavior and dielectric properties of hyperbranched poly(phenylene oxide)/cyanate ester resins

A novel hyperbranched poly(phenylene oxide) (HBPPO) modified 2,2′‐bis(4‐cyanatophenyl) isopropylidene (BCE) resin system with significantly reduced curing temperature and outstanding dielectric properties was developed, and the effect of the content of HBPPO on the curing behavior and dielectric properties as well as their origins was thoroughly investigated. Results show that BCE/HBPPO has significantly lower curing temperature than BCE owing to the different curing mechanisms between the two systems, the difference also brings different crosslinked networks and thus dielectric properties. The dielectric properties are frequency and temperature dependence, which are closely related with the content of HBPPO in the BCE/HBPPO system. BCE/2.5 HBPPO and BCE/5 HBPPO resins have lower dielectric constant than BCE resin over the whole frequency range tested, while BCE/10 HBPPO resin exhibits higher dielectric constant than BCE resin in the low frequency range (<104 Hz) at 200°C. At 150°C or higher temperature, the dielectric loss at the frequency lower than 102 Hz becomes sensitive to the content of HBPPO. These phenomena can be attributed to the molecular relaxation. Two relaxation processes (α‐ and β‐relaxation processes) are observed. The β‐relaxation process shifts toward higher frequency with the increase of temperature because of the polymer structure and chain flexibility; the α‐relaxation process appears at high temperature resulting from the chain‐mobility effects.