NOVELTY - A copolymer is obtained by copolymerizing a monomer mixture comprising 30 mol% or more carbonyl group-containing monomer (a1) (I) and 20 mol% or more monomer (a2) containing polymerizable double bonds and polar groups with respect to 100 mol% of total amount of monomer mixture. The monomer (a2) does not contain (meth)acryloyl group.    USE - Copolymer is used in baking paste composition used in manufacture of sintered material e.g. green sheet used in manufacture of laminated ceramic capacitor (all claimed) used in formation of circuit used in plasma display device, liquid crystal display device, and solar cell.    ADVANTAGE - The copolymer has excellent compatibility with respect to solvent, and provides baking paste composition with excellent thixotropic property, pseudo-plastic characteristics, coatability, baking property, and fluidity during coating, and desired viscosity, which enables formation of coating film with excellent surface smoothness. The formation of threads during the coating of baking paste composition is suppressed.    DETAILED DESCRIPTION - A copolymer is obtained by copolymerizing a monomer mixture comprising 30 mol% or more carbonyl group-containing monomer (a1) of formula (I) and 20 mol% or more monomer (a2) containing polymerizable double bonds and polar groups with respect to 100 mol% of total amount of monomer mixture. The monomer (a2) does not contain (meth)acryloyl group.    R1=H or methyl;and    R2=branched 4-18C cycloalkyl or 6-18C aryl optionally substituted by alkyl.    INDEPENDENT CLAIMS are included for the following:    (1) baking paste composition, which contains the copolymer (A), a solvent (B), and an inorganic powder (C);    (2) green sheet, which contains the baking paste composition and a base material; and    (3) manufacture of sintered material, which involves coating the baking paste composition on base material, drying the coated baking paste composition, and baking the laminate of baking paste composition and base material after the drying process.