Journal of Applied Polymer Science, Vol.73, No.3, 353-361, 1999
Phosphorus-containing epoxy resin for an electronic application
A phosphorus-containing epoxy resin, 6-H-dibenz[c,e] [1,2] oxaphosphorin-6- [2,5-bis(oxiranylmethoxy)phenyl]-6-oxide (DOPO epoxy resin), was synthesized and cured with phenolic novolac (Ph Nov), 4,4'-diaminodiphenylsulfone (DDS), or dicyandiamide (DICY). The reactivity of these three curing agents toward DOPO epoxy resin was found in the order of DICY > DDS > Ph Nov. Thermal stability and the weight loss behavior of the cured polymers were studied by TGA. The phosphorus-containing epoxy resin showed lower weight loss temperature and higher char yield than that of bisphenol-A based epoxy resin. The high char yields and limiting oxygen index (LOI) values as well as excellent UL-94 vertical burn test results of DOPO epoxy resin indicated the flame-retardant effectiveness of phosphorus-containing epoxy resins. The DOPO epoxy resin was investigated as a reactive flame-retardant additive in an electronic encapsulation application. Owing to the rigid structure of DOPO and the pendant P group, the resulting phosphorus-containing encapsulant exhibited better flame retardancy, higher glass transition temperature, and thermal stability than the regular encapsulant containing a brominated epoxy resin. High LOI value and UL-94 V-0 rating could be achieved with a phosphorus content of as low as 1.03% (comparable to bromine content of 7.24%) in the cured epoxy, and no fume and toxic gas emission were observed.
Keywords:phosphorus-containing epoxy resin;6-H-dibenz[c,e] [1,2]oxaphosphorin-6-;[2,5-bis(oxiranylmethoxy)phenyl]-6-oxide;phenolic novalac;4,4 ' -diaminodiphenylsulfone;dicyandiamide;bisphenol-A;flame retardant;limiting oxygen index;UL-94V test