the present invention relates to a method of producing low density polydi resins having high yield strengths and the products thereof . in particular a polydiene resin , such as dihydroxyl terminated 1 , 2 - polybutadiene is reacted at room temperature with an organic chain extender , such as hexamethylene - 1 , 6 - diisocyanate , and a graft comonomer such as n - vinyl - 2 - pyrrolidone in the presence of a peroxide free radical initiator , such as o , o &# 39 ;- bis diisopropylbenzene , whereby a elastomeric material having the peroxide and a graft comonomer dispersed therethrough is produced . at a subsequent period of time , the elastomeric material can be exposed to elevated temperatures whereupon the elastomer is cured to a low density resin having a high yield strength .