Formaldehyde polymerizes in aqueous solution to give paraformaldehyde, HO--(CH2O)nH. Although high molecular weights are achieved, the polymer

Question:

Formaldehyde polymerizes in aqueous solution to give paraformaldehyde, HO--(CH2O)nH. Although high molecular weights are achieved, the polymer "unzips" readily. However, if the polymer is treated with acetic anhydride, the resulting material (an important commercial polymer called Delrin) no longer "unzips." Explain the chemistry described.