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A series of novel phosphaphenanthrene/ phenylsiloxane bigroup macromolecules (DDSi-n) were synthesized and applied to obtain high-performance epoxy thermosets. DDSi-n macromolecules simultaneously enhanced the anti-impact and flame-retardant performance of epoxy thermosets. The impact strength of the DDSi-n-containing thermoset (DDSi-n/EP) was maximally increased by nearly 140% in 8% DDSi-1/EP because of the flexible phenylsiloxane block and the polar phosphaphenanthrene group interacting with matrix in DDSi-n macromolecules. Meanwhile, the evidently elevated anti-ignition and self-extinguishing performance, the suppressed combustion heat, and the enhanced charring capability of DDSi-n/EP were all caused by the flame-retardant group synergistic effect of phosphaphenanthrene and phenylsiloxane groups of DDSi-n macromolecules in thermosets. Compared with the individual phosphaphenanthrene or phenylsiloxane group in monogroup contrasts, the phosphaphenanthrene and phenylsiloxane groups in bigroup DDSi-n macromolecules were disclosed to synergistically work to toughen and flame-retard epoxy thermosets more efficiently. The working results of bigroup DDSi-n macromolecules in thermosets reveal a superior way to construct high-performance materials.

A series of flame‐retardant rigid polyurethane foams (RPUFs) containing dimethyl methylphosphonate (DMMP) and expandable graphite (EG) were prepared by box‐foaming. The RPUFs were characterized by thermogravimetric analysis (TGA), the limiting oxygen index (LOI), cone calorimeter, and scanning electron microscope (SEM). The decomposition process of DMMP was investigated by Pyrolysis‐Gas Chromatography/Mass Spectroscopy (Py‐GC/MS). Accordingly, their flame retardant behaviors and mechanism were also discussed. The results show that the DMMP/EG system can linearly enhance the LOI value from 19.2% of the pure RPUF to 33.0% of RPUFs containing 16 wt% flame retardant. In addition, the DMMP/EG system also remarkably increases yields of the residual char and drastically decreases the peak value of heat release rate (PHRR), heat release rate (HRR), total heat release (THR), total smoke release (TSR), and the yields of CO (COY). In the flame retardant RPUFs, when the matrix is ignited, the flame retardant DMMP should be decomposed to gaseous PO2 fragments, which can inhibit free radical chain reaction of flammable alkyl free radical from the decomposed matrix; whereas the flame retardant EG can rapidly expand and form loose and worm‐like expanding graphite char layer accordingly, which can hinder the heat transmission to the inner matrix and reduce decomposing velocity of matrix. After the combination of the two flame retardant effects, the DMMP/EG flame retardant system provides the matrix with better flame retardant effects than one of them does. Namely, it shows excellent gas‐condensed bi‐phase synergistic effect. POLYM. COMPOS., 35:301–309, 2014. © 2013 Society of Plastics Engineers

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