ted by the formula (1) is identical with the aforesaid constituent unit (1). [0161] In the formulas (4) and (5), R5 is a hydrocarbon group, such as a saturated or unsaturated hydrocarbon group, an alicyclic hydrocarbon group or an aromatic hydrocarbon group, and examples of such hydrocarbon groups include the same groups as previously described with respect to R3 in the formula (3). [0162] In the