Flame–retarded epoxy resin with high glass transition temperature cured by DOPO-containing H-benzimidazole

Abstract

A halogen-free flame retardant of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-containing H-benzimidazole (DHBI) was synthesized and subsequently used as co-curing agent of 4,4′-diamino-diphenylmethane for diglycidyl ether of bisphenol-A. The structure of DHBI was characterized by Fourier transform infrared (FTIR) spectroscopy, proton, carbon 13 and phosphorus-31 nuclear magnetic resonance, and mass spectroscopy. A series of cured epoxy resins (EPs) were prepared and their flame retardancy, thermal stability, flexibility, and dielectric properties were investigated. The resulting cured EP (EP-10) with 7.45 wt% of DHBI successfully achieved UL 94 V-0 rate with limited oxygen index of 35.6% and without dropping phenomenon. Compared with the cured pristine EP (EP-00), the glass transition temperature of EP-10 was increased by 6.9°C, accompanied with an enhancement of flexible strength by 13.1 MPa and a decrement of dielectric constant by 0.3 at the testing frequency of 1 MHz.

Flame retardant and toughening behaviors of bio‐based DOPO‐containing curing agent in epoxy thermoset

“…9,10‐dihydro‐9‐oxa‐10 phosphaphenanthrene‐10‐oxide (DOPO) was verified as an effective phosphorus‐containing flame retardant for epoxy thermoset. Due to excellent flame retardant effect of DOPO‐based derivatives, they had received outstanding attentions in flame retardant thermosets . Currently, some researchers designed DOPO derivatives with different structures to prepare flame retardant epoxy thermosets; those flame retardants showed excellent flame retardant efficiency …”

A novel curing agent based on diphenylphosphine oxide for flame-retardant epoxy resin

“…22 –30 For example, the derivatives prepared by the reaction of DOPO with Schiff base can be used as intumescent reactive flame retardants because both phosphorus and nitrogen exist in one structure. 31 –34 Xu et al prepared a phosphorus/nitrogen-containing co-curing agent called D-bp which modified the EP thermoset, which in turn exhibited excellent flame retardancy at low phosphorus content. However, the thermal stability of the EP resins decreased greatly with the increase in phosphorus content.…”

Reactive cyclic phosphonamide flame retardant for epoxy resins

“…Some of them have in fact reached the final stage of commercialization. For example, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide and its derivatives have long been the workhorse of nonhalogenated flame‐retardant EP . However, the reactivity of these phosphorus‐containing flame retardants inevitably changes the curing chemistry of EP.…”