Vinyl polymer, process for producing vinyl polymer, thermosetting coating composition, and coating material

A vinyl polymer having a weight-average molecular weight of 1,500 to 10,000 which is obtained through: a first step in which a starting-material mixture containing a vinyl monomer is continuously fed to a first tank reactor of the continuous operation type and the vinyl monomer is polymerized at a polymerization temperature of 150 to 300 DEG C for a residence time of 1 to 60 minutes until the conversion into polymer reaches 50 to 99% to produce an intermediate reaction mixture; and a second step in which 0.01 to 5 parts by weight, per 100 parts by weight of the vinyl monomer, of a polymerization initiator and the intermediate reaction mixture are fed to a second reactor and the vinyl monomer is further polymerized at a polymerization temperature of 100 to 200 DEG C for a residence time of 10 to 240 minutes until the conversion into polymer reaches 80% or higher.