A polymer compound of a block polymer containing at least three block segments each having a repeating unit structure comprising a polyalkenyl ether structure comprises a repeating unit structure having a silyl ether side chain represented by the formula (1) in at least one block segment of the block polymer and a repeating unit structure containing one kind or two or more kinds of either a side chain having an ionic functional group represented by the formula (2) or an ester-type functional group obtained by esterifying the ionic functional group in at least one other block segment. ##STR00001##