identical to or different from each other, is a hydrogen atom or a hydrocarbon group having a carbon number of 1-4, wherein a ratio of the hydrocarbon atom number with respect to the hydrocarbon group number in R1 and R2 is 0.15 or less. [0015] In the present invention, the oxyalkylene group AO and the oxyethylene group EO are preferably added each other in a random form. [0016] In the composition