A modifier represented by Formula 1: wherein, in Formula 1, R 1, R 4, and R 5 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, R 2 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 3 is a connecting group represented by Formula 2 or Formula 3, wherein, in Formula 2 or Formula 3, R 6 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms; or a substituent represented by Formula 2-1, R 7 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 8 to R 10 are each independently a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with an alkyl group having 1 to 20 carbon atoms, wherein, in Formula 2-1, R 11 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 12 and R 13 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms. R 1, R 4, and R 5 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, R 2 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 3 is a connecting group represented by Formula 2 or Formula 3, R 6 is a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms; or a substituent represented by Formula 2-1, R 7 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 8 to R 10 are each independently a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with an alkyl group having 1 to 20 carbon atoms, R 11 is a divalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms, and R 12 and R 13 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which is substituted or unsubstituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, and an aryl group having 6 to 30 carbon atoms.