Several aldehydes have been tested as substitutes for the lachrymator formaldehyde in the THPOH/ammonia process. Aldehydes such as acetaldehyde or butyraldehyde promote rapid polymer formation without being incorporated into the finish. Chloral is incorporated to a limited extent, but the finish is sensitive to base. To gain further insight into the polymer-forming process, the reactions of THP and its aldehyde derivatives with ammonia have been investigated in vitro. There is evidence that THP acts as a difunctional reagent, regardless of the aldehyde, forming a linear polymer with a single phosphorus, nitrogen, and oxygen atom in each repeating unit.