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Fire hazard and waste crisis are two challenges for thermosets, particularly for epoxy resins (EPs) possessing the largest market share therein; yet it is beset with difficulties to solve the challenges simultaneously. Herein, a commercialized phosphorus-containing diol named diethyl bis(2-hydroxyethyl)aminomethylphosphonate (DAP) with "trinity" structures containing phosphonate ester, primary hydroxyls and tertiary amine was applied in an epoxy-anhydride curing system to achieve the catalyst-free mixed transesterification within the adaptable carboxylate/phosphonate networks. The phosphonate structure in DAP was covalently bonded into the epoxy vitrimers (EVs), endowing the EVs with intrinsic fire safety. In detail, the peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP) and maximum smoke density (Ds max) values were considerably reduced by 62.0%, 73.6%, 78.9% and 70.8%, respectively. Meanwhile, owing to the self-catalytic tertiary amine and highly reactive primary hydroxyls from DAP, the mixed transesterification within the adaptable carboxylate/phosphonate networks was accelerated, endowing facile reprocessibility and malleability of the vitrimers, which were further degraded into low-mass molecules by simple alcoholysis. Killing two birds with one stone, this work provided a promising and feasible way to make sustainable and fire-safe thermosetting polymers with comprehensive properties. [Display omitted] • Catalyst-free adaptable carboxylate/phosphonate networks were used to construct intrinsically fire-safe epoxy vitrimers. • The vitrimers exhibited observable suppression on heat, smoke and toxic gas during burning. • The vitrimers showed desirable malleability without sacrificing intrinsic fire safety. • Degradation of the vitrimers was achieved via simple alcoholysis, showing multi-path recyclability. [ABSTRACT FROM AUTHOR]

Flame retardancy and recyclability are two important issues in the research field of thermosets, particularly for epoxy resin (EP) with the biggest market share. It is of great importance, but rarely achievable, to integrate these properties simultaneously into EP. Herein, we report a facile way to prepare intrinsically flame-retardant epoxy vitrimers combining rapid recycling and multiple shape memory effects by introducing dynamic ester-linkages with catalytic transesterification activity into the crosslinking networks of EP. The flame-retardant epoxy vitrimers exhibited high T g (∼110.7 °C), desirable thermal stability and excellent flame retardancy with UL-94 V-0 rating, and high LOI of ∼34%. Also, the value of the peak heat release rate (PHRR) and the total heat release (THR) showed 63% and 32% reduction, respectively. Meanwhile, flame-retardant epoxy vitrimers showed high malleability that could be reprocessed in 15 min at 200 °C without sacrificing the mechanical properties and flame retardancy. Moreover, the dynamic transesterification network allowed flame-retardant EP to access multiple shape memory effect. The design of flame-retardant epoxy vitrimers provide a prime example to foster the cyclic utilization of flame-retardant thermosetting polymers. [Display omitted] • A facile strategy was proposed to prepare intrinsically flame-retardant epoxy vitrimers. • The epoxy vitrimers owned high T g , desirable thermal stability and excellent flame retardancy. • The epoxy vitrimers displayed fast recyclability (∼15 min) without loss in flame retardancy and mechanical properties. • The multiple shape memory performance of the epoxy vitrimers was easily manipulated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel phosphorus-containing transition metal complexes were designed as latent curing agents for EP. • The cured EP thermosets revealed excellent comprehensive fire-safety performance among the related literature. • Dielectric properties of the EP thermosets were improved by introducing the symmetric complexes, especially in high frequencies. Concerning the application of fire-safety epoxy resin (EP) in electrical and electronic devices, a question may inevitably arise: how can fire hazards be reduced without compromising comprehensive properties? Herein, this work presented a solution to fabricate intrinsic fire-safety EPs with attractive properties by introducing phosphorus-containing transition metal complexes as multifunctional curing agents. Cured with 15 wt% DPPSSZn, the EP thermoset exhibited superb fire safety performance, and the testing samples achieved a V-0 rating in the UL-94 vertical burning test and possessed an upgraded LOI value of 36.5%. Additionally, the peak heat release rate (pHRR) and the total smoke production (TSP) showed 71.4% and 74.3% decreases, respectively. Similar results were found in the system by replacing Zn with Co ions. Furthermore, the prepared EP possessed latent curing behaviors within 90 days with rather low complex viscosity. Lower dielectric constant and dielectric loss factors were obtained owing to the uniform dispersion and the relatively low polarized networks enabled by the reactive metal complexes. Hence, this work proposed a feasible and simple strategy for developing intrinsic fire-safety thermosets with desirable comprehensive properties. [ABSTRACT FROM AUTHOR]