Disclosed are: a
polyolefin polymer having a polar group represented by the general formula (i), which is produced by modifying, with a high degree of modification rate, a
double bond in a
polymer that has the
double bond at one terminal, at both terminals, or in the inside of its
polymer chain and is produced by a known method; a method for producing the
polyolefin polymer; and a water dispersionmaterial and a mold
release agent composition each comprising the
polyolefin polymer. (i) wherein PO represents a polyolefin polymer produced by the
polymerization of a
monomer comprising an ethyleneor an olefin having 3 to 20 carbon atoms, wherein a group inside the parentheses represents a polar group; A and B independently represent any one selected from R1, a cyano group, C(O)OR1 and C(O)NR1R2, provided that A and B may together form a cyclic structure; M represents a
metal cation or an
onium cation; j represents the number of the
metal cation(s) or the
onium cation(s), and is an integerof 0 to 4; i represents the number of valency of the
metal cation or the
onium cation, and is an integer of 0 to 4; D and E independently represent any one selected from an
oxygen atom, a
nitrogen atom, a
sulfur atom, R3, OR3, SR3 and NR3R4, provided that D and E may together form a cyclic structure; d and e represent the number of valency of the
substituent D and the number of valency of the
substituent E, respectively, and independently represent an integer of 0 to 4; R1, R2, R3 and R4 independently represent any one selected from a
hydrogen, an optionally substituted
alkyl, alkenyl, alkynyl, aralkyl or
aryl group having 20 or less carbon atoms, and a group having a heterocyclic ring; and n represents the average number of the functional groups, and is a number of 0.80 to 10.0.