Synthesis of High-Tg, Flame-Retardant, and Low-Dissipation Telechelic Oligo(2,6-dimethylphenylene ether) Resins for High-Frequency Communications

An intrinsic flame-retardant moiety, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), is incorporated into oligo(2,6-dimethyl-1,4-phenylene ether) (OPE), and four phosphorus-containing telechelic OPE resins are synthesized. The first is synthesized with a para phenyl methacrylate end group (OPE-PM); the second is synthesized with para and meta phenyl methacrylate end groups (OPE-OPM); the third is synthesized with a para vinyl benzyl ether end group (OPE-VBE); and the fourth is synthesized with para and meta vinyl benzyl ether end groups (OPE-OVBE). All the self-cured samples showed good flexibility, high temperature (Tg = 216 to 250 °C, Td5% > 400 °C), and water resistance (0.25%). The self-cured OPE-OPM and OPE-OVBE show outstanding low dielectric values of 2.63 and 2.65 and impressive low dissipation factors of 0.0035–0.0047 at 10 GHz, respectively. The results indicate that a further crosslinking behavior in the chain end can enhance the rigidity and further enhance the dielectric properties. Most importantly, all phosphinated thermosets show excellent burning resistance, and both UL-94 VTM and microscale combustion calorimetry experiments were conducted to explain the flame-retardant behavior. We believe that this work will contribute greatly to the research related to polymeric substrate materials for 5G technology.