Monomeric butadienyl ethers formed as fission products when an acetalization product of crotonaldehyde is subjected to a heat treatment in the liquid phase (see Group IV (b)) are polymerized during the splitting process by means of a polymerization contact agent. The acetalization products of crotonaldehyde are defined as crotonaldehyde dialkyl acetals and trialkoxy butanes. Specified contact agents which promote the polymerization of the monomer formed in addition to promoting the splitting process itself are kaolin, Fuller's earth, Tonsil, clay and hydrosilicates. In examples, (1) 1,1,3-triethoxy butane is heated with Tonsil in a flask fitted with a dephlegmator column, the greater part of the butadienyl ether product being obtained as residue in polymeric form whilst some monomeric butadienyl ether is removed as distillate along with the ethanol split off; (2) as in (1) except that the mixture is heated under reflux without removing a distillate. The residue is then divided into two portions one of which is fractionated without removing its Tonsil content whilst the other portion is fractionated after removing the Tonsil. In both cases the butadienyl ether is obtained in polymeric form but most of the starting product remains unchanged. German Specification 726,407 is referred to.ALSO:Alkoxy derivatives of butene and butadiene are obtained by subjecting an acetalization product of crotonaldehyde to a heat treatment in the liquid phase. The acetalization products of crotonaldehyde are defined as crotonaldehyde dialkyl acetals and trialkoxy-butanes. It is advantageous to distill off continuously the monomeric butadienyl ethers or crotonaldehyde diacetals formed along with the alcohol split off. The splitting process can be assisted by using an acetal-splitting catalyst or a contact agent having a large surface. Catalysts referred to are iron and lead hydroxides, carbonates of metals, the hydroxides of alkali metals or alkaline earth metals and organic bases. The process may also be carried out in the presence of an inert liquid, e.g. in the pressure of tricresyl phosphate. If ethoxy-butadienes are desired in monomeric form contact agents such as active carbon and silica gel which do not catalyse the polymerization should be used. Contact agents such as kaolin, fuller's earth, Tonsil, clay and hydrosilicates promote polymerization of the monomer formed by the splitting process in addition to promoting the splitting process itself (see Group IV (a)). If the formation of crotonaldehyde diacetals is to be promoted the fission catalyst should be used in smaller amount than is required for the complete formation of butadienyl ethers. In examples: (1) crotonaldehyde dibutyl acetal is heated at 240-247 DEG C. in a flask fitted with a dephlegmator column and the butanol formed continously withdrawn, butadienyl butyl ether remaining as residue; (2) 1,1,3-trimethoxybutane is heated in a flask fitted with a dephlegmator column and containing a finely pulverized catalyst consisting of active carbon impregnated with ammonium dihydrogen phosphate. The butadienyl methyl ether and methanol split off are removed continuously and at the end of the reaction a further quantity of 1,1,3-trimethoxybutane is added to the residue and the reaction continued as before, this procedure being repeated eleven times; (3) 1,1,3-triethoxybutane is heated in a flask as in (2) except that the finely pulverized catalyst consists of active carbon impregnated with sodium ammonium acid phosphate, the product being butadienyl ethyl ether; (4a) 1,1,3-triethoxy butane is heated with Tonsil in a flask fitted with a dephlegmator column, the greater part of the butadienyl ether product being obtained as residue in polymeric form whilst some monomeric butadienyl ether is removed as distillate along with ethanol; (4(b)) as in 4(a) except that the mixture is heated under reflux without removing a distillate. The residue is then divided into two portions one of which is fractionated without removing its Tonsil content whilst the other portion is fractionated after removing Tonsil. In both cases the butadienyl ether is obtained in polymeric form but most of the starting material remains unchanged; (4(c)) as in 4(a) except that the amount of Tonsil is reduced, the amount of monomeric butadienyl ether formed being thereby increased; (5) 1,1,3-triethoxybutane is heated in a flask as in 4(a) but in the absence of a catalyst, the yield of butadienyl ether being very low. A small amount of Tonsil is then added and the heating continued for a further period while removing the azeotropic mixture of ethanol and butadienyl ether which is obtained in increased yield whilst the residue contains the polymeric ether; to obtain crotonaldehyde diacetal small amounts of Tonsil are used; (6) 1,1,3-triethoxy butane is heated as in 4(a) with a catalyst prepared by impregnating active carbon with sodium ammonium acid phosphate, the product being crotonaldehyde diethyl acetal; (7) 1,1,3-trimethoxybutane is heated as in 4(a) with a finely pulverized catalyst consisting of active carbon impregnated with phosphoric acid and water, the product being crotonaldehyde dimethyl acetal; (8) 1,1,3-trimethoxybutane is introduced into the bottom of a glass vessel charged with tricresyl phosphate and heated to 200 DEG C. A distillate is obtained containing butadienyl methyl ether and some crotonaldehyde dimethyl acetal. When the same procedure is carried out in the presence of a finely pulverized catalyst consisting of active carbon impregnated with primary ammonium phosphate suspended in the tricresyl phosphate the yield of butadienyl ether is increased. German Specification 726,407 is referred to.ALSO:In the production of alkoxy derivatives of butene and butadiene by subjecting an acetalization product of crotonaldehyde to a heat treatment in the liquid phase (see Group IV (b)), the acetal splitting catalysts that may be used include active carbon impregnated with sodium ammonium acid phosphate or primary ammonium phosphate, the catalyst being used in finely pulverized form.