Process for polymer production

A continuous process for producing a polymer of reduced molecular weight which comprises subjecting a halogenated butyl polymer selected from chlorinated butyl rubber and brominated butyl rubber and having a number average molecular weight (M.sub.n) of from about 85,000 to about 150,000 to mastication in an extruder at a temperature of from about 140.degree. to about 200.degree. C. while being exposed to and in contact with an atmosphere containing from about 0.1 to about 4 volume per cent of ozone for a time sufficient to produce a reduced molecular weight polymer wherein the halogenated butyl polymer contains at least about 75 percent of the unsaturation in the EXO methylene configuration, said extruder is selected from twin screw and single screw extruders, said mastication is characterized by a shear rate of at least about 575 to about 1900 sec.sup.-1, and said reduced molecular weight polymer has an M.sub.n of from about 10,000 to about 40,000.