A P/N/Si-containing hyperbranched flame retardant for improving mechanical performances, fire safety, and UV resistance of epoxy resins

The applications of epoxy resin (EP) are limited in many high-tech fields due to its unsatisfied fire safety and mechanical properties, but introducing flame retardants usually further deteriorates mechanical properties. In this work, a flame-retardant hyperbranched polymer SD was synthesized from 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), diethanolamine, polyformaldehyde, and phenyltrimethoxysilane (PTMS), and applied in high-performance EP. The results showed that the resultant EP-SD samples maintain high transparency and show improved UV-shielding performances. 1.5 wt% of SD allows EP to achieve a vertical burning UL-94 V-0 classification, indicative of high efficiency. EP-SD6 with 6 wt% SD obtains a limiting oxygen index (LOI) of 36.0 % and its peak heat release rate (PHRR) and peak smoke release rate (PSPR) are 65.4 % and 20.2 % lower than those of the neat EP. The addition of SD also improves the mechanical properties of EP. The tensile strength, elongation at break, flexural strength and impact strength of EP-SD6 are increased by 70.4 %, 68.4 %, 30.2 % and 59.7 %, respectively. The superior flame retardancy and mechanical properties of EP-SD6 enable it to stand out from flame-retardant EP systems. Therefore, this work provides a rational design strategy for preparing fire-safe EPs with great optical and mechanical properties based on hyperbranched polymers, which can satisfy the requirements of different industries.