The invention provides new compositions of matter that are capable of forming cross-linked polymeric materials upon reaction with various known epoxy-containing compositions. Thus, the compositions of this invention are useful in the manufacturing of prepregs and laminates for PWB applications among many other uses. Preferred compositions of this invention include substituted hydroxyarylphosphine oxide mixtures, the glycidyl ether derivatives, or the epoxy resin oligomer adducts derived therefrom. The materials provide for laminates that have higher glass transition temperatures, improved thermal stability, and that are free of halogen.