a structure of phosphorous - containing functionalized poly , a preparation method thereof , and a composition prepared therefrom are provided . the curable composition includes an unsaturated monomer and a phosphorous - containing functionalized poly having a polymerizable group and a molecular weight between 500 and 20 , 000 . the composition provides excellent fluidity and fast curing rate . after curing , the composition exhibits excellent low dielectric coefficient and dielectric loss , high heat resistance and flame retardancy . it is suitable for prepregs , laminated sheets for printed circuits or the like .