PROCESSES FOR TRANSITIONING BETWEEN VARIOUS POLYMERIZATION CATALYSTS

The invention relates to processes for transitioning from a first polymerization reaction with a first catalyst system to a second polymerization reaction with a seco nd catalyst system where the first and second catalyst systems are incompatible. The polymerization reaction is conducted in a polymerization zone of a gas phase fluidized bed reactor which contains a fluidized bed of polymer particles by an essentially continuous passage of monomer gases through the polymerization zone. The process comprises a) discontinuing the introduction of the first catalyst system into the reactor; b) lowering the height of the bed of polymer particles from a first height to a second height; c) conducti ng essentially concurrently with the reduction of the bed height, at least one modification which is reducing the partial pressure of the monomer gases within the polymerization zone from a first partial pressure to the second lower partial pressure or introducing a n alkoxylated amide or amine into the reactor; d) introducing the second catalyst system into the reactor; and e) increasing the bed height to a level above the level of the second height.