Copolymer and antifouling coating composition containing the same

A vehicle resin for an antifouling coating composition,

• the vehicle resin being a copolymer comprising:
• a structural unit (A) derived from a polymerizable monomer (a) having a silicon atom-containing group represented by the following formula (1):
• [in the formula (1), R1, R2, and R3 each independently represent a hydrocarbon group having a carbon number of 1 to 6];
• and
• a structural unit (B) derived from a polymerizable monomer (b) copolymerizable with the polymerizable monomer (a),
• wherein the polymerizable monomer (a) is a monomer represented by the following formula (2):
• [in the formula (2), R1, R2, and R3 each independently represent a hydrocarbon group having a carbon number of 1 to 6, and R4 represents a hydrogen atom or a methyl group],
• a content of the structural unit (A) is greater than or equal to 50 mass % and less than or equal to 60 mass % in 100 mass % of the copolymer,
• a content of the structural unit (B) is greater than or equal to 40 mass % and less than or equal to 50 mass % in 100 mass % of the copolymer,
• the structural unit (B) includes a structural unit derived from a (meth)acrylate containing an alkoxy group and/or an oxyalkylene chain in ester moiety thereof, and
• an acid value derived from free carboxy group is greater than or equal to 0.1 KOHmg/g and less than or equal to 60 KOHmg/g.