Esterification Oligomerization of Phosphaphenanthrene Biphenol Caused Efficient Flame Retardant Effect of Group Aggregation in Epoxy Resin
Xiao Wu, Hui Zhu, Wang Xi, Yong Qiu, Juan Li, Lijun Qian
Abstract
The efficient and simple synthetic method prepared several linear phosphaphenanthrene biphenol oligomers DQPC-n (n = 1, 2, 4) to explore the effects of phosphaphenanthrene groups with different aggregation amounts on flame retardant behavior in epoxy resin. The aggregated phosphaphenanthrene groups in DQPC-n bring epoxy resins with better flame retardancy than phenol compound DOPO-HQ. The limited oxygen index values of epoxy resins with DQPC-n were more than 35.8% and obtained a V-0 rating in the UL 94 test, while that with DOPO-HQ only passed a V-1 rating at the same phosphorous content. Simultaneously, DQPC-n showed efficient flame retardancy in the cone calorimeter test. Especially, the DQPC-1 with moderate aggregated phosphaphenanthrene groups exerted a better flame inhibition effect in epoxy resin, and the values of THR, TSP, and av-EHC of the DQPC-1/EP were lower than that of DOPO-HQ/EP. The mechanism results demonstrated that the pyrolysis of DQPC-1 concentrated released more phosphorus-containing fragments to prevent the combustion chain reaction process. In addition, DQPC-1 can facilitate the aromatic residue formation in the condensed phase. Therefore, the aggregation effect of the phosphaphenanthrene groups in this thesis provides a method for developing efficient epoxy resin additives.