US 9,217,919 B2  138  137  A molecular weight of the compound represented by the  general formula (Al) is preferably from 200 to 2,000, and  especially preferably from 400 to 1,000.  (A4)  OH  (A3)  OH  o=l=}F  F  I  N- \  F  O=S  II  F  0 F  (A2)  OH  OH  (Al) -continued  OH  (A5)  OH  (A6)  0 ~0H  lf  (A7)  (AS) 