Method for preparing polymer

A method of preparing a polymer, the method comprising:

• supplying a monomer stream and a solvent stream to a reactor and performing a polymerization reaction to prepare reaction product;
• supplying a reactor discharge stream to a separation device, separating a gaseous stream including an inert gas in the separation device, and supplying a liquid stream including the reaction product from which the inert gas is removed to a volatilization device;
• separating a polymer from a lower discharge stream from the volatilization device and supplying an upper discharge stream including an unreacted monomer, a solvent, and an inert gas to a condensation unit;
• and
• condensing and separating the unreacted monomer and the solvent in the condensation unit and supplying a gaseous stream to a vacuum unit,
• wherein a content of the inert gas in the gaseous stream discharged from the separation device is 80 wt % or more,
• wherein a content of the inert gas removed as the gaseous stream in the separation device is 75% to 99% relative to a content of the inert gas included in the reactor discharge stream supplied to the separation device,
• wherein a content of the inert gas in a liquid stream discharged from the separation device is 10 ppm to 150 ppm,
• wherein the separation device has an operation temperature of 130° C. to 150° C. and an operation pressure of 1.5 kgf/cm2g to 3.5 kgf/cm2g,
• wherein a content of the inert gas in a gaseous stream output from the condensation unit is from 100 ppm to 600 ppm, and
• wherein the inert gas is nitrogen.