The present invention provides a compound of formula (I), (II), or (III), wherein R¹, R², R², R³, and R³ are the same or different and each is H an alkyl, an alkenyl, an alkynyl, a cycloalkyl, an aryl, or an aralkyl. Alternatively, either of R² or R² combined with either of R³ or R³ comprises a ring. R⁴ is a protecting group or a solid support R⁵ is H or an alkyl. R⁶ is a protecting group, an amidoalkyl, an alkyl, an alkyl ketone, an alkenyl, an alkynyl, a cycloalkyl, an aryl, or an aralkyl. R¹⁵ is H or a protecting group. Q and Q¹ are the same or different and each is a nucleoside, an oligonucleotide comprising a nucleoside, or an oligomer comprising a nucleoside, which is of formula (a) or (b), wherein B is a labeling group, an alkyl, an alkenyl, an alkynyl, a cyclic group optionally containing one or more heteroatoms, or an amino; and, E is H, a halogen, a hydroxy, an alkoxy, an ester, an amino or a protecting group. X and X¹ are independently O, S, or Se, and n is an integer from 1 to about 300. Each Q in each monomeric unit defined by n can be the same or different. The present invention further provides a method of preparing a polymer using the N-acylphosphoramidite of formula (I) or (II).