Method of preparing heat-resistant resin, heat-resistant resin and heat-resistant ABS resin composition

A method of preparing a resin, the method comprising:

• polymerizing a vinylcyan compound-based first part comprising 70 to 80 parts by weight of a first monomer and 30 to 20 parts by weight of a vinylcyan compound monomer and having a glass transition temperature of 140° C. or more, a number average particle diameter of 300 to 700 Å, and a weight-average molecular weight of 200,000 to 300,000 g/mol;
• and
• polymerizing a vinylcyan compound-based second part, the second part enveloping the first part comprising the first monomer and the vinylcyan compound monomer,
• wherein the resin comprises 30 to 80 parts by weight of the first part and 70 to 20 parts by weight of the second part, and has a glass transition temperature of 135 to 145° C. and a weight-average molecular weight of 100,000 to 150,000 g/mol.