an ultra low loss dielectric thermosetting resin composition has at least one cyanate ester component and at least one reactive intermediate component that is capable of copolymerization with said component . the invention is a cyanate ester resin of the form : t n - f / 1 − f - w ] n − 1 - f / 1 − f - f / 1 − f ] n + 2 , wherein t is a 1 , 3 , 5 - substituted - triazine moiety ; w is a linking atom between triazine and either component a or component b ; z is component ; h is component ; ocn is a cyanate ester end group ; r is a reactive end group of component b ; n is an integer greater than or equal to 1 ; and f is a weight or mole fraction of component a . the composition exhibits excellent dielectric properties and yields a high performance laminate for use in high layer count , multilayer printed circuit board , prepregs , resin coated copper , film adhesives , high frequency radomes , radio frequency laminates and various composites .