A polymer includes a repeating unit represented by Formula (1) and/or a repeating unit represented by Formula (2), and a repeating unit represented by Formula (3) and/or a repeating unit represented by Formula (4), where a proportion of a total of the repeating unit represented by Formula (1) and the repeating unit represented by Formula (2) is greater than 0 mol % but ≤100 mol %; a proportion of a total of the repeating unit represented by Formula (3) and the repeating unit represented by Formula (4) is ≥0 mol % but less than 100 mol %; a proportion of a total of the repeating unit represented by Formula (1) and the repeating unit represented by Formula (3) is ≥20 mol %; and a proportion of a total of the repeating unit represented by Formula (2) and the repeating unit represented by Formula (4) is ≤80 mol %.