Abstract: A block copolymer of propylene can be obtained with its quality controlled uniform by conducting at first continuous polymerization of propylene in a polymerization system, receiving a polymer slurry, which has been discharged continuously from the polymerization system, in a batchwise polymerization tank, feeding ethylene to the tank to conduct batchwise polymerization of ethylene and propylene. Upon discharge of a copolymer slurry formed by the preceding batchwise polymerization, at least a predetermined amount of unreacted ethylene is left over in the tank. Into the tank with the unreacted ethylene still left over therein, there are simultaneously charged the polymer slurry from the polymerization system and a deactivator. During this charging, ethylene is not supplied.

Abstract: A block copolymer of propylene is produced by using propylene itself as a liquid medium, conducting continuous polymerization (former-stage polymerization) of propylene alone or propylene and a small amount of ethylene at first and then conducting batchwise copolymerization (latter-stage polymerization) of ethylene and propylene. The amount of an activity improver to be added to a polymerization tank for the latter-stage polymerization and/or the polymerization time of the latter-stage polymerization are controlled in accordance with the amount of a slurry transferred from a polymerization tank for the former-stage polymerization to the polymerization tank for the latter-stage polymerization so as to maintain the ratio of the amount of the polymer polymerized by the former-stage polymerization to the amount of the polymer polymerized by the latter-stage polymerization constant in the block copolymer.

Abstract: Disclosed herein is a method for controlling the polymerization temperature in a polymerization apparatus equipped with a cooling system in which steam, which has occurred in the presence of a volatile liquid medium in a reaction system, is condensed in a reflux condenser and the resulting noncondensable gas and condensate are then returned to the reaction system, thereby removing the polymerization heat. A portion of the noncondensable gas is recirculated to the cooling system. The flow rate of the noncondensable gas to be recirculated and the flow rate of a cooling medium to be introduced into the reflux condenser are controlled in accordance with the temperature of the reaction system.

Abstract: Polymer powder is separated from a carrier gas by separating the polymer powder from the carrier gas in a cyclone separator, drawing the thus-separated polymer powder through a bottom part of the separator into a hopper, feeding out the polymer powder by a rotary feeder from the hopper while controlling the revolution speed of the rotary feeder in accordance with the powder level in the hopper, and controlling the volume of a purge gas, which is introduced into a polymer powder guide extending between the separator and the hopper for the prevention of plugging thereof, in accordance with the revolution speed of the rotary feeder. The height of the top of the powder in the hopper is maintained at a predetermined constant level.