a process is provided for making metallated and substituted alkynes from feedstocks which include alkadienes containing allenic unsaturation or such alkadienes in a mixture with alkynes having either internal or terminal unsaturation , such as a mixture of propadiene and propyne . this reaction involves an initial step in which the allenic hydrocarbon and any internal alkyne is isomerized and simultaneously the resultant terminal alkynes are metallated with an alkali metal . the reaction is carried out at relatively low temperatures in a suitable inert solvent such as diethylether . when metallation is complete the reaction mixture can be contacted directly with any suitable electrophile , such as a halo silane , for example , chlorotrimethylsilane , and the alkali metal on the terminal alkyne is replaced with the desired substituent . the products thus formed are useful as monomers for preparing polymers having a variety of properties , for example , as asymmetric membranes for gas separation .