Poly(phosphorus‐silicon‐alkyne): Widening the application potential in epoxy resin with excellent flame retardancy, mechanical property, and unimpaired thermal stability

Abstract

Aimed at promoting the flame retardancy of epoxy resin (EP) and widening its applications, a novel flame retardant, poly(phosphorus‐silicon‐alkyne) (PPSA), is synthesized from poly(silicon‐alkyne) and 9,10‐dihydro‐9‐oxa‐10‐phenanthroline‐10‐oxide (DOPO) to modify EP. The structure of PPSA is characterized by Fourier transform infrared and 1H nuclear magnetic resonance. The PPSA introduction into EP significantly improves its chemical and physical properties. When containing 2.5–10 phr of PPSA, the modified EP achieve better flame resistance capability than neat EP. In particular, EP/PPSA‐5.0 reaches a limiting oxygen index value of 31.2% and passes vertical burning test (UL‐94) V‐0 rating at the same time. The total heat release and total smoke production are lowered by 31.1% and 24.9%, respectively. In addition, the initial decomposition temperature (T5%) of the modified EP is basically unchanged thanks to good stability of PPSA. Characterization of char residues generated in the combustion of EP/PPSA reveals that PPSA protects the EP from fire by diluting flammable gas with phosphorus free radicals and forming compact thermal stable layer containing silicon and phosphorus. Subsequently, measurements of mechanical properties show that impact strength and flexural strength are markedly improved by PPSA incorporation. Therefore, PPSA modifies EP to obtain excellent thermal stability and mechanical properties, justifying an outstanding flame retardant with comprehensive properties.

A Rigid–Flexible and Multi-Siloxane Bridge Strategy for Toughening Epoxy Resin with Promising Flame Retardancy, Mechanical, and Dielectric Properties

“…Figure 7 shows the Raman curves of the char residues, where there were two special absorption peaks at 1350 cm −1 and 1590 cm −1 , belonging to peak D and peak G, respectively. The intensity ratio of the D-band to the G-band (I D /I G ) is usually used to analyze the degree of graphitization of the carbon layer, and a lower ratio of I D /I G indicates a higher degree of graphitization and better carbon structures and thermal-oxidative stability [ 52 , 53 , 54 , 55 , 56 ]. The I D /I G value of DPB/EP-0 was 2.81, while the values gradually decreased with the addition of DPB, reaching the lowest value of 2.57 when the amount of DPB was 7.5 phr.…”