Aldehyde polymers are probably the oldest synthetic polymers [1–8]. Polyoxymethylene, the polymer of formaldehyde, was first described by Butlerov in 1859 and the polymer of chloral was first prepared in 1832 by Liebig. This was about one century before the concept of linear macromolecules was developed. Polyformaldehyde and polychloral were isolated because they were stable at room temperature and above.