Using various techniques, polyynes with "n" up to 4 or 5 were synthesized during the 1950s. Around 1971, T. R. Johnson and D. R. M. Walton developed the use of end-caps of the form −, where R was usually an ethyl group, to protect the polyyne chain during the chain-doubling reaction using Hay's catalyst (a copper(I)–TMEDA complex). With that technique they were able to obtain polyynes like with "n" up to 8 in pure state, and with "n" up to 16 in solution.