Low dielectric and flame-retardant properties of thermosetting redistributed poly(phenylene oxide)

A curable low-molecular-weight poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was prepared by the redistribution of regular PPO with maleic anhydride (MA) in toluene, using benzoyl peroxide as an initiator. The redistributed PPO (MA-PPO), which contained alkene groups, was characterized by proton nuclear magnetic resonance and Fourier transform infrared spectroscopy. The redistributed PPO oligomers with reactive double bonds were cured with triallylisocyanurate (TAIC) and/or a phosphorus-containing allyl-functionalized monomer (allyl-DOPO). Electrical properties of cured resins were studied by using a dielectric analyzer. The glass transition temperatures were measured by dynamic mechanical analysis. The flame retardancy was determined by the UL-94 vertical test. The effects of curing accelerator and the amounts of TAIC and allyl-DOPO incorporated into the network on the dielectric properties, glass transition temperature, and flame retardancy of the resulting systems were investigated. The results indicated that MA-PPO cured with TAIC exhibited low dielectric constants (2.23-2.58 at 1 GHz) and dissipation factors (0.0034-0.0039 at 1 GHz) but had high glass transition temperatures (171-197°C). The MA-PPO/TAIC copolymerized with allyl-DOPO could achieve a flame retardancy rating of UL-94 V-0 at about 1.35 wt % of phosphorus. The redistributed PPO/TAIC resins have potential applications in the fabrication of printed circuit boards.