The oxidation of sealing liquids has been examined in order to select the best temperatures and times for dissolving macromolecular polyisobutylene P-200 in I-20A industrial oil. Conclusions are drawn on the desirability of maintaining a temperature in the reactor in the range 110-120A degrees C for 5-6 h in the dissolution of the polyisobutylene. Temperatures above 120C, even acting briefly, lead to extensive decomposition of the macromolecular polyisobutylene.