Method of storing antioxidant mixture

A method of storing an antioxidant mixture, comprising storing an antioxidant mixture containing an antioxidant and an aluminum compound represented by the following formula (3):

• AlR3 (3)
• wherein R moieties each independently represent a halogen atom or an alkyl group having 3 or more carbon atoms,
• wherein the antioxidant is an antioxidant represented by the following formula (1) or formula (2):
• wherein:
• n represents an integer of 1 to 4,
• R1 and R2 each independently represent a C1-20 hydrocarbyl group or a hydrogen atom,
• R and R′ each represent a C1-20 hydrocarbylene group, and
• A represents a C1-30 n-valent hydrocarbon group;
• or
• wherein:
• R3, R4, R6, and R7 each independently represent a hydrogen atom, a C1-8 alkyl group, a C5-8 cycloalkyl group, a C6-12 alkylcycloalkyl group, a C7-12 aralkyl group, or a phenyl group, R5 represents a hydrogen atom or a C1-8 alkyl group,
• X represents a single bond, a sulfur atom, or a —CHR8— group where R8 represents a hydrogen atom, a C1-8 alkyl group, or a C5-8 cycloalkyl group,
• A′ represents a C2-8 hydrocarbylene group, and
• either one of Y or Z represents a hydroxyl group and the other represents a hydrogen atom or a C1-8 alkyl group, and
• wherein the antioxidant mixture is suitable for olefin polymerization.