Abstract: A flame retardant suitable for manufacturing a polymer composition is provided. The polymer composition is used for forming a cured film in which a balance among flame retardancy, adhesion, chemical resistance, heat resistance, and elasticity, and so on, is provided. A flame-retardant polymer composition with an excellent balance among the above properties is also provided. The flame retardant of the invention has a structure of Formula (1), (2), or (3): (in which, R1 is hydrogen or methyl, R2 is C2-20 alkylene or C2-20 alkylene in which any —CH2— is replaced by —O—, R3 and R4 are C1-20 alkyl, phenyl, and phenyl substituted by C1-5 alkyl or phenyl, R3 and R4 may also be an integrally-formed cyclic group, and p and q are 0 or 1).