Poly(n-butylamino) (di-allylamino) phosphazenes were prepared by the reaction of samples of (NPCl2)(n) having a molecular weight of either 5 x 10(4) or 10 x 10(6) with n-butylamine, and di-allylamine. Films were prepared by the casting method, and the molecular weight dependence of properties of the film were determined with an Erma refractometer, an oxygen gas permeater, and a tensilon and reho-vibron-orientec. It was found that the refractive index of the film did not depend on the molecular weight and n-butylamine or di-allylamine contents. Also, the glass transition temperature of the films decreased with increasing di-allylamine content. The oxygen gas permeability D-k value increased with increasing di-allylamine content. However, a plot of the Young’s modulus values versus amine contents or D-k values did not produce a straight line. In order to make a film having the highest D-k value, the polymer has to have an antisymmetric structure.