Study of the structures of butadiene polymers produced on initiation by Lewis acids

Butadiene has been polymerized by AlCl3 and related materials at −78°C. The structure of the polymers produced has been studied by infrared analysis. The structure of the soluble polybutadiene was found to be independent of extent of conversion, concentration of catalyst solution, and length of reaction. An insoluble polymer also formed in the system and the amount of this depended on the extent of conversion, being greater at higher conversion whether this was achieved by higher catalyst concentration or longer time. Complexing the AlCl3 with nitroethane or nitrobenzene changed the structure of the polymer slightly, while the use of diethyl ether as a complexer produced no changes. TiCl4, used as the initiator, produced polymers of slightly different structure from those formed with AlCl3, while AlBr3 and BF3·Et2O yielded polymers like those from AlCl3. When the solvent used was varied, the polymer structure also varied. The observed variations were small in all cases.