Industrial autothermal cationic isobutylene polymerization reactors may present very complex dynamic behavior and difficult operation. A mathemathical model was developed to describe the operation of an autothermal solution industrial reactor, and some possible sources of complex dynamical behavior were analyzed. The results obtained indicate that the most probable source of the complex behavior observed industrially is the existence of adventitious impurities in the feeed stream. The effects caused by the presence of adventitious impurities on process operation and product properties were investigated for both polymerization and oligomerization. In the first case, impurities influence the reactor productivity but do not change the polymer quality. In the oligomerization, both the polymer quality and the reactor productivity are seriously affected by the existence of impurities in the feed stream.