improved radiation curable polyurethanes are provided that are polymerizable crystalline polymers having terminal ethylenic unsaturation , relatively low molecular weights and that rapidly crystallize , are prepared from the reaction product of certain polyester glycols and diisocyanates to form an isocyanate - terminated prepolymer that is then reacted with an ethylenic unsaturated alcohol to form the ethylenic unsaturated crystallizable polymer , or in the alternative , the polyester glycol is reacted with an ethylenic unsaturated monoisocyanate to form the polymerizable crystallizable polymer , that can be used as such for example in preparing magnetic tape , as such , or in admixture with other materials , and which can be applied to a substrate from a melt , or formed by molding , extrusion , and then cured with appropriate energy as an electron beam .