Enhanced flame retardant and dielectric properties of oligo(2,6-dimethyl-1,4-phenylene ether) resins through DOPO derivative incorporation

Owing to their low-dissipation factor, oligo(2,6-dimethyl-1,4-phenylene ether) (OPE) resins are commonly used to prepare copper-clad laminates (CCL) for high-frequency communication devices. To further improve the dielectric properties, some low-dielectric rubbers such as styrene-ethylene-butylene-styrene (SEBS) are generally added by industries. This highly flammable rubber makes it necessary to add flame-retardant additives to achieve UL-94 V-0 certification. Some of these additives are halogen-based, causing adverse effects on biological systems. To mitigate this, we report curable telechelic OPEs containing 9,10-dhydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-derivatives (intrinsic fire retardance) with low-dielectric properties for high-frequency communication devices. We synthesized four types of phosphinated OPEs (POPEs) and categorized them into two sets: the first set is POPE-PM (phenyl methacrylate end groups), and POPE-VBE (vinyl benzyl ether end groups), then the second set is POPE-APM (both allyl and phenyl methacrylate end groups), and POPE-AVBE (both allyl and vinyl benzyl ether end groups), and investigated the structure-property relationship. UL-94 and MCC assessments revealed that the integration of phosphinate into OPE thermosets raises their flame-retardant capacity. Importantly, this integration does not alter their core properties of thermal steadiness, hydrophobic capacity, mechanical hardness, and lower dielectric attributes. All the thermosets derived from POPE resins showed competitive or better thermal properties over commercial OPEs resins (SA9000 from SABIC and OPE-2St from MGC). Particularly, thermosets derived from allyl-group containing resins POPE-APM and POPE-AVBE showed enhanced Tg, flame-retardant, dielectric properties, and low moisture absorption properties over ally-free ones.