ne group, R4-Z-Y1???X1???(2) R4-Z-X2???(3) In general formulas (2) and (3), R4 represents an alkyl group having 8 to 16 carbon atoms, Z is a functional group represented by chemical formula (i) or (ii), Y1 represents ???(CH2CH2O)n???, ???(CH2CH(CH3)O)p???, or the combination of ???(CH2CH2O)n??? and ???(CH2CH(CH3)O)p???. n and p are integers of 1 to 6 when Y1 represents ???(CH2CH2O)??? or ???(CH2CH