A polyisobutene composition having a global maximum of the differential molecular
weight distribution curve at a molecular weight Mmax of from 3 500 to
8 000 is described, which comprises at least one local maximum at a molecular weight
of from 112 to 560. The isobutene oligomers present act as flow improvers and boiling
assistants. They are added to higher molecular weight isobutene polymers, preferably
before or in the course of a distillation, for removing unconverted isobutene and/or
an inert diluent.
