Fundamental studies on cationic polymerizations i. the inversion temperature

The low‐temperature AlCl3‐initiated polymerization of isobutene has been investigated. Direct evidence of the occurrence of chain‐breaking reactions is presented. The polymer molecular weight can be affected by changes in reaction temperature between ‐35 and −78°C. at the same conversion level. The discovery of inversion temperature (Ti) is described. At Ti, the molecular weight becomes independent of monomer concentration. We call Ti the temperature level at which the dependence of product molecular weight on the monomer concentration changes its sign. The inversion temperature has been observed in methyl chloride, ethyl chloride, and vinyl chloride, and vinyl choride diluents. A theory explaining the phenomenon is postulated. It is suggested that competing chain breaking process having dissimilar activation energies determine the molecular weight. Their effects cancel each other at Ti. The previously reported, unusual inverse relation existing between molecular weight and monomer concentration is explained by the concept of Ti.