A magnolol-derived bisphosphate (MBDPP) was successfully synthesized from the substitution reaction between magnolol and diphenyl phosphoryl chloride. MBDPP was subsequently applied for the fabrication of intrinsically anti-flammable bismaleimide (BMI) thermosets. The effect of MBDPP on the curing kinetics of BMI systems was investigated by the non-isothermal DSC technology, showing that the addition of MBDPP increased the reaction activation energy of the BMI system owing to the steric hindrance of MBDPP. With only 2 wt% of MBDPP, the BMI thermoset achieved an LOI of 35.0% and UL-94 V-0 grade. Besides, the PHRR, MARHE, THE, TSP and mean SEA of the BMI thermoset with 2 wt% of MBDPP were declined by 26%, 33%, 27%, 34% and 50%, respectively, compared to those of the unmodified BMI. The enhanced anti-flammability and smoke suppression performances of the BMI thermosets were attributed to the formation of an intact, expansive and thermally resistant char layer by the presence of MBDPP. Such a char layer effectively blocked the transportation of combustible degradation products to the flame and the thermal radiation of heat to the polymer matrix, so as to slow down the heat release rate and smoke emission.
In order to improve the efficiency of β -CD, the inclusion complex of β -CD and resorcinol bisdiphenylphosphate (RDP) ( β -CD@RDP) was prepared, which β -CD was as the host component and RDP was as the guest. The structure and thermal stability property of β -CD@RDP was also characterized. EP/ β -CD@ RDP composites were prepared by adding β -CD@RDP into EP matrix. The results of thermogravimetric test showed that the flame retardant systems could effectively increase the corresponding temperature of EP matrix to reach the maximum thermal decomposition rate, and exhibited good char-forming property. When the amount of β -CD@RDP in EP was 20wt%, the limiting oxygen index (LOI) value of EP was increased to 26.5% from 19.8%, and the vertical burning test (UL-94) reached V-1 level. The cone calorimeter test indicated that 20wt% loading in EP could reduce the peak of heat release rate (PHRR) and the total heat release (THR) of EP by 94.7% and 93.4% respectively, and the peak of smoke production rate (PSPR) and the total smoke production (TSP) was reduced by 16.7% and 22.2%, respectively. Therefore, the addition of β -CD@RDP could reduce the fire risk of EP effectively.
The thermal degradation of resorcinol bis(diphenyl phosphate) (RDP) and bisphenol A bis(diphenyl phosphate) (BDP) has been studied by 31 P NMR, Q-TOF, and GPC at normal and extreme heating conditions. The thermal degradation begins with the elimination reaction that generates reactive monomers and arynes. The aryne-bisphosphate adducts or their decomposition products were identified through Q-TOF analysis. Through the intertwined condensations, transesterifications, and elimination reactions, the reactive acid phosphates are formed and eventually convert the bisphosphates into volatile triphenyl phosphate, oligomeric aryl/acid polyphosphates, and non-volatile polyphosphoric acid. It is these reactions and products that provide the bisphosphates effective pathways for entry into the vapor phase or action in the condensed phase. The facility of these reactions, particularly the elimination reaction that is the initiation step, to occur is critical for the high efficiency of flame retardancy displayed by the bisphosphates. A thermal Melvin rearrangement of the bisphosphates to arylphosphonates has also been established.
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