It is an object to provide a film having both high transparency and high heat resistance, and particularly a coating solution for forming a coating film from which an optical film can be produced. A triaroylbenzene-skeleton polymer in which a terminal of a polymer produced by polymerizing a compound of Formula [1] below is modified by a compound of Formula [2] below. A coating solution for forming a coating film, comprising the polymer. A film obtained from the coating solution for forming a coating film. In the formulae below, X1 is a divalent group of Formula [1a], Formula [1b], or Formula [1c] below (where Y1 and Y2 are independently a C1-2 alkylene group; n is an integer of 1 to 6; and m is an integer of 1 to 6), X2 is divalent benzene, thiophene, furan, or fluorine, and X3 is a hydrogen atom, a halogen atom, CF3, a C1-6 alkoxy group, or a C1-6 alkyl group.