Organoclay compositions which comprise the reaction product of a smectite-type clay having an ion exchange capacity of at least 50 meq. wt. per 100 g. clay (active basis), and mixture of a quaternary ammonium compound and a chain transfer agent which is a thiol, .alpha.-methylketone, .alpha.-methylalcohol or a halogen compound are useful agents for use in the processes for the preparation of thermoplastic materials.