An addition-cleavage oligomer of the general formula Z-By-A- (BA) x-BA-By-Z, wherein the A monomer unit is derived from a diester or diacid, and the B monomer unit is Derived from a bifunctional monomer having a functional group that co-reacts with the acid group or ester group of the A monomer, x + y is 0 to 60, Z includes an ethylenically unsaturated polymerizable group, and among the A or B monomers Addition-cleavage oligomers, wherein at least one of comprises a 1-methylene-3,3-dimethylpropyl group. [Selection figure] None一般式 Z-By-A-(B-A)x-B-A-By-Zの付加開裂オリゴマーであって、式中、Aモノマー単位がジエステル又は二酸に由来し、Bモノマー単位が、Aモノマーの酸基又はエステル基と共反応する官能基を有する二官能性モノマーに由来し、x+yが0~60であり、Zがエチレン性不飽和重合性基を含み、A又はBモノマーのうちの少なくとも1つが1-メチレン-3,3-ジメチルプロピル基を含む、付加開裂オリゴマー。【選択図】なし