(Poly)alkylene glycol-containing compound

A polyalkylene glycol-containing compound comprising:

• a hydrophobic structural moiety (A);
• a polyalkylene glycol moiety (B);
• and
• one lactam ring-containing structural unit (C), in its structure,
• wherein the polyalkylene glycol-containing compound is represented by the following formula (2):
• wherein R5 is a hydrocarbon group having a carbon number of 4 or greater and optionally containing at least one heteroatom;
• R8 is a hydrogen atom or a hydrocarbon group having a carbon number smaller than that of R5 and optionally containing at least one heteroatom;
• R6 is a structure represented by the following formula (4) or (4′);
• wherein x is 0, y is 0 or 1, and z is a number of 0 to 5;
• R7s are the same as or different from each other and are each a C2-C20 alkylene group;
• X2 is direct bond, an ester group, an ether group, a carbonyl group, a carbonate group, or a group represented by the following formula (10):
• wherein Z1 and Z2 are each a hydrogen atom or hydroxy group, with one of Z1 or Z2 being a hydrogen atom and the other being a hydroxy group;
• X3 is a urethane group, an ester group, an ether group, a carbonyl group, a carbonate group, an isocyanate group or an amide group;
• n2 is a number of 5 to 100;
• and w2 is a number of 1 to 3,
• wherein the at least one heteroatom in each of R5 and R8 is a nitrogen atom, a sulfur atom, a phosphorus atom, or a halogen atom,
• a proportion of a total mass of R8 other than a hydrogen atom and R5 is 2.5 to 60% by mass in 100% by mass of the polyalkylene glycol-containing compound.