A polymer consisting mainly of structural units represented by the general formula (1), wherein the total molar amount of terminal aldehyde groups and acetal groups is 0.6 mol% or smaller based on the total molar amount of the structural units represented by the general formula (1). -[-(-CHR 1 -) n -CX 1 R 2 -CX 2 R 3 -]-(1) (In the formula, n is an integer of 2 to 10; X 1 and X 2 each represents -H, -OH, or a functional group capable of being converted into -OH, provided that at least one of X 1 and X 2 is hydroxy or a functional group capable of being converted into hydroxy; and R 1 , R 2 and R 3 each represents -H or C 1-5 alkyl, aryl, aralkyl, or heteroaryl and the two or more R 1 's may be different).