Modified bio-related substance, process for producing the same, and intermediate

Provided is a polyalkylene glycol derivative substantially containing no secondary hydroxyl group and being represented by the following formula (p): wherein each R is a hydrocarbon group having 1 to 24 carbon atoms, the groups represented by R being the same or different from each other in one molecule, OA 1 and each OA 2 are oxyalkylene groups having 2 to 4 carbon atoms, the groups represented by OA 2 being the same or different from each other in one molecule, and n and m are each average number of moles of the oxyalkylene group added, n represents 0 to 1000, and m represents 10 to 1000. The above derivative may be prepared by debenzylating a compound of the formula (4): wherein R, OA 1 , OA 2 , n and m are as defined above, the polyalkylene glycol derivative of formula (p) satisfying the following parameter: Hrd / Mp × 1000000 ‰ 3 wherein Mp is the molecular weight corresponding to the peak top obtained from gel permeation chromatography of the derivative of formula (p), and Hrd is the ratio of hydroxyl group residue contained in the alkyl group R at the polyoxyalkylene chain terminal end at the 2- and 3-positions of the compound of the formula (4).