Method of preparing aromatic vinyl-unsaturated nitrile-based copolymer and aromatic vinyl-unsaturated nitrile-based copolymer prepared using the same

A method of preparing an aromatic vinyl-unsaturated nitrile-based copolymer of an injection molding resin, in which a content of an oligomer is less than 0.5 parts by weight based on 100 parts by weight of the copolymer, a content of a residual monomer is less than 1,000 ppm, and a content of a structural unit derived from unsaturated nitrile monomers in the copolymer is in a range of 22 to 30 wt %, the method comprising:

• preparing a polymerization product by adding a polymerization initiator into a mixed solution prepared by adding an aromatic vinyl-based monomer and an unsaturated nitrile-based monomer into a reaction solvent, and then performing polymerization at 115 to 135° C. until a monomer conversion ratio is 80% or more;
• and
• performing a devolatilization process on the polymerization product,
• wherein the aromatic vinyl-based monomer and unsaturated nitrile-based monomer are used in a weight ratio of 65:35 to 78:22, and
• the polymerization initiator includes an organic peroxide having a 1 hour half-life temperature in a range of 100 to 120° C. and is used in an amount of 0.01 to 0.08 parts by weight based on 100 parts by weight of total monomers,
• wherein a molecular weight regulator is further included in an amount of 0.21 to 0.27 parts by weight based on 100 parts by weight of the total monomers during the polymerization, and whereupon a fogging haze of the injection molding resin is less than 2.0 as measured according to ASTM 1003.