the stirrer 3 was driven to stir the mixture when the temperature of the reaction liquid reached 140 u00b0 c the conduit 7 and the outlet 8 were closed an outlet 15 from which the reaction liquid was drawn and an inlet 20 for the recycling liquid were opened the reaction liquid was recycled at a flow rate of 1 kg min by means of a liquid circulation pump 16 in a circuit including a tubular mixer 16 static mixer valves amounted to pipes from an alkylene oxide reservoir 12 and from a pump 13 for feeding a definite amount of an alkylene oxide were then opened and 2 9 kg of propylene oxide was introduced at a blowing rate of 87 g min into the reactor through a blowing nozzle 18 over a period of about 35 minutes the reaction was continued for 10 minutes and unreacted materials and the gaseous component were taken out by passing the reaction mixture through a partial condenser 9 and a total condenser 10 the desired unsaturated polyester was obtained in a yield of 99 and had an acid value of 30 in this method the maximum reaction pressure in the reactor 1 was recorded as 0 8 kg cm 2 the reaction was carried out under the same conditions using the same apparatus as described above except that the reactor 1 was not confined in this case the yield and acid value of the resulting unsaturated polyester were almost equal to.