A curable composition, comprising:
- 100 parts by weight of a polyisobutylene-based polymer (A) having 1.2 or more (meth)acryloyl groups per molecule;
- 15 to 900 parts by weight of a polyisobutylene-based polymer (B) having 0.5 to 1.0 (meth)acryloyl group per molecule;
- and
- 0.001 to 50 parts by weight, per 100 parts by weight of the total weight of the polymer (A) and the polymer (B), of a polymerization initiator (C),
- wherein each of the polymer (A) and the polymer (B) have a number average molecular weight of 500 to 500,000 as measured by size exclusion chromatography based on polystyrene standards, and a molecular weight distribution (weight-average molecular weight Mw)/(number-average molecular weight Mn) of 1.0 to 2.0,
- wherein the polymer (A) includes one or more selected from the group consisting of polymers represented by the following general formulas (1) and (3) to (6):
- where, independently, R1 represents a divalent or higher alkyl-substituted benzene having a free valence at the benzylic position or a divalent or higher-valent alkylene group having 4 to 20 carbon atoms and a free valence on a tertiary carbon, A represents a polyisobutylene-based polymer;
- R2 represents a divalent saturated hydrocarbon group having 2 to 6 carbon atoms and containing no heteroatoms, R3 and R4 each represent hydrogen, a monovalent hydrocarbon group having 1 to 20 carbon atoms, or an alkoxy group, R5 represents hydrogen or a methyl group, and n represents an integer of 2 or greater, and
- the polymer (B) includes one or more selected from the group consisting of polymers represented by the following general formulas (2) and (7) to (10):
- where, independently, R6 represents a monovalent alkyl-substituted benzene having a free valence at the α-position of alkyl or an alkyl group having 4 to 20 carbon atoms and a free valence on tertiary carbon, A represents a polyisobutylene-based polymer, R2 represents a divalent saturated hydrocarbon group having 2 to 6 carbon atoms and having no hetero atoms, R3 and R4 each represent hydrogen, a monovalent hydrocarbon group having 1 to 20 carbon atoms, or an alkoxy group, and R5 represents hydrogen or a methyl group.