Preparation And Properties Of Phosphorus-containing Flame-retardant Latent Epoxy Resins

A phposphorus-containing epoxy resin(DOPOER) was synthesized byDOPO and bisphenol A type epoxy resin. Dicyandiamide(DICY) or2-(2-dimethylaminothethoxy-4,4,5,5)-tetramethyl-1,3,2-dioxaborolane(PDB) was used as latent curing agents ofDOPOER to obtain an one-pot epoxy resin with good latency and fire resistance.The vertical flame test and the limiting oxygen index test were used to characterize the flame-retardant performance of DOPOER-DICY series.DOPOER-DICY-1.5 system with phosphorus content of 1.5wt%passed UL-94 V-0 and its LOI value achieved 34.6%. The gelation time at 60℃ was 9days. The curing mechanism of DOPOER-DICY system was studied by non-isothermal DSC method. The results showed that the activation energy(Ea) was 125.9 kJ/mol and autocatalytic mechanism existed in the system. The TGA results showed that with the increasing phosphorus content, the initial degradation temperature decreased gradually. The initial degradation temperature(Td,5%) of DOPOER-DICY-1.5 is 335.3℃ and the maximum weight loss temperature(Td,max)of DOPOER-DICY-1.5 is393.7℃. The DMA results showed that with the increasing phosphorus content, the glasstransition temperature(Tg) of DOPOER-DICY systems rose in the first stage, and then decreased. Theglasstransition temperature of DOPOER-DICY-1.5 is 139.0℃.The DOPOER-PDB systems showed even better performances in latency, thermal stability and dynamic mechanic properties. With the phosphorus content of 1.5 wt%, the gelation time at 60?Cof PDB/DOPOERsystems became 15 d and passed UL-94 V-0 and the LOI reached 35.6%. The TGA results exhibited that with the increasing phosphorus content, the initial degradation temperature decreased gradually. The initial degradation temperature(Td,5%), the maximum weight loss temperature(Td,max) and the char yield of DOPOER-DICY-1.5 is 335.3?C,393.7?C and 18.0%, respectively. The DMA results showed that the glasstransition temperature(Tg) of DOPOER-DICY-1.5 is 117.0?C. While adding more phosphorus contents, the tensile strength and bending strength increased gradually. Compared to pure system, the tensile strength and bending strength of the DOPO-PDB-1.5 increased by 58% and 27.1%, respectively while the impact strength were maintained. The TGA-FTIR, SEM pictures and cone calorimetry results proved that during the combustion, DOPOER-PDB resin could produce phosphoric-acid-type dehydrating agent, accelerating the polymer charring, and that most of the phosphorus gathered in the surface to form compact carbon layers, which prevented the oxygen from permeating inside. In addition, the flammable gas was restrained to release and thus reduced the process of thermal degradation and improved its fire retardancy.