An acrylamide derivative of the following general formula (I) is used to prepare a polymer or copolymer:wherein R1 represents a hydrogen atom, a straight-chain or branched alkyl group containing 1 to 4 carbon atoms or a C3-6 cycloalkyl group, R2 and R3 each independently represent an alkylene group containing 1 to 6 carbon atoms or R2 and R3 may be combined to form a ring, X represents a hydrogen atom, an amino group, a hydroxyl group, a halogen atom, a carboxyl group or a -COOR4 group wherein R4 represents a C1-6 straight-chain or branched alkyl, C3-6 cycloalkyl, phenyl, substituted phenyl, benzyl or substituted benzyl group, and Y represents an amino group, a halogen atom, a carboxyl group or a -COOR4 group wherein R4 represents a C1-6 straight-chain or branched alkyl, C3-6 cycloalkyl, phenyl, substituted phenyl, benzyl or substituted benzyl group. The thus obtained polymer or copolymer is a polymer or hydrogel incorporating many functional groups while maintaining the sensitive temperature response.