Abstract: Methods for producing rubbery polymers are disclosed comprising forming a slurry of such rubbery polymers, preferably butyl rubber prepared from a mixture of a C.sub.4 to C.sub.8 isoolefin and a C.sub.4 to C.sub.10 conjugated mutiolefin in a low temperature reaction zone in the presence of a Friedel-Crafts catalyst and an organic halide diluent, passing that slurry into an overflow passage for transporting the slurry to a recovery system, and injecting a mixture of a hydrocarbon liquid having a boiling point above the boiling point of the organic halide and a polar organic catalyst quenching agent into said overflow passage at a point adjacent to the outlet from the reaction zone in order to prevent continued production of polymer in the overflow passage and to maintain the overflow passage substantially free of agglomerates.