The cyclopolymerization of 1,5-hexadiene with ethylaluminum dichloride and diethylaluminum chloride-vanadylbis-(acetylacetonate) catalysts has been described more recently. This chapter describes synthesis of heterocyclic polymers via cyclopolymerization. The cyclopolymerization of some similar compounds has been reported. Diacrylamide has been polymerized in solution, using a radical initiator. The polymer was soluble in hot dimethylformamide and contained only a small amount of double bond. The synthesis of cyclopolymers containing heterocyclic rings by cyclopolymerization of dialdehydes has been published. Cyclopolymerization of symmetrical and unsymmetrical 1,5- and 1,6-diolefin monomers has been reported. Among the compounds studied were divinylacetals and vinyl crotonate. Work on the polymerization of 1,3-bis(4-vinylphenyl)propane and similar compounds has been reviewed. The initial observation that 1,6-hexadienes do cross-link, but undergo cyclopolymerization was made during an attempt to synthesize strongly basic ion exchange resins. The preparation of hydrocarbon soluble polymers from the polymerization of 1,5-hexadiene with the triisobutylaluminum-titanium tetrachloride catalyst system was reported in 1958.