Organolithium cleavage of aliphatic polyethers, polysulfides and polyimines

Organolithium compounds and other Group IA organometallics cleave high molecular weight poly(alkylene oxides) very rapidly at room temperature in dilute benzene solution. This reaction also works on a dimeric polyepoxide such as bis(2‐n‐butoxyethyl)ether and much less readily on a monomeric one as 1,2‐dimethoxyethane. On the other hand, a simple aliphatic monoether such as di‐n‐butyl ether is not cleaved under conditions several orders of magnitude more drastic than were effective on the polyethers. The mechanism for this facile polyether cleavage is proposed as a β‐elimination in which the organolithium is greatly activated by chelation with the main‐chain oxygen atoms of the polyether. This cleavage method has been used broadly on high molecular weight polyethers to obtain quantitative yields of hydroxyl‐ended, amorphous, and crystalline polyethers (Mn = 500–10,000), many of which cannot be made by direct polymerization. Aliphatic polysulfides and an N‐substituted aliphatic polyamine cleave by this same method to, respectively, mercapto‐ended and secondary amine‐ended polymers. The mechanism aspects of these results are discussed.