Preparation method of super absorbent polymer

A method of preparing a super absorbent polymer, comprising

• forming a hydrogel polymer by cross-linking polymerization of a water-soluble ethylene-based unsaturated monomer having at least partially neutralized acidic groups in the presence of an internal cross-linking agent, an encapsulated foaming agent, and a polymerization initiator;
• coarsely pulverizing the hydrogel polymer after mixing with a carboxylic acid-based additive;
• drying and pulverizing the coarsely pulverized hydrogel polymer to prepare a powdery base resin;
• and
• further cross-linking a surface of the powdery base resin in the presence of a surface cross-linking agent to form a surface cross-linked layer,
• wherein the carboxylic acid-based additive comprises at least one selected from the group consisting of a carboxylic acid represented by Chemical Formula 1 and a salt thereof:
• wherein in Chemical Formula 1,
• A is C5 to C21 alkyl,
• B1 is —OCO—, —COO—, or —COOCH(R1)COO—,
• B2 is —CH2—, —CH2CH2—, —CH(R2)—, —CH═CH—, or —C≡C—,
• R1 and R2 are each independently C1 to C4 alkyl,
• n is an integer of 1 to 3, and
• C is a carboxyl group.