Polyoxypropylenglycol and 4,4¢-diphenylmethandiisocyanate cooligomers obtaining process is studied. It is established that reaction proceed by the mechanism of migratory polymerisation based on joining to the nitrogen atom of 4, 4¢- diphenylmetandiisocyanate of the mobile hydrogen atoms of polyether. It is shown that blending of cooligomer with a copolymer of isobutylene and isoprene increases elasticity, thermal and chemical stability, adhesive and physical-mechanical properties of composites and decreases shrinkage. Blends of cooligomer with a butyl rubber are recommended as the highly adhesive, high-elasticity covering, as well gluing and packing composite