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.sub.1--).sub.n--CX.sub.1R.sub.2--CX.sub.2R.sub.3-]-- (1) (In the formula, n is an integer of 2 to 10; X.sub.1 and X.sub.2 each represents --H, --OH, or a functional group capable of being converted into --OH, provided that at least one of X.sub.1 and X.sub.2 is hydroxy or a functional group capable of being converted into hydroxy; and R.sub.1, R.sub.2, and R.sub.3 each represents --H or C.sub.1-5 alkyl, aryl, aralkyl, or heteroaryl and the two or more R.sub.1's may be different).