Methylol adduct formation

Formaldehyde fixes proteins in tissue by reacting with basic amino acids— such as lysine,5 7—to form methylol adducts. These adducts can form crosslinks through Schiff base formation. Both intra- and intermolecular cross-links are formed,8 which may destroy enzymatic activity and often immunoreactiv-ity. These formaldehyde-induced modifications reduce protein extraction efficiency and may also lead to the misidentification of proteins during proteomic analysis. 

The general definition of a condensation reaction is a one that involves product formation by expulsion of water (or other small molecule) as a by-product. By this definition, activation and methylolation are also condensations. In more precise terms the chain-building process should be described as a condensation polymerization, however, in the jargon of the phenolics industry, the term condensation is usually reserved for the chain-building process. This terminology is not necessarily observed in the literature [88]. Many literature reports correctly refer to methylolation as a condensation reaction. The molecular weight development of the phenol alcohol adducts may also be classified as a step-polymerization. 

Proban 210 and Pyrovatex CF are the most important durable FRs. The former is an adduct of tetrakis(hydroxy methyl) phosphonium chloride (THPC) with urea and the latter is N-methylol dimethyl phosphonopropionamide. Both operate only in the cellulose pyrolysis stage of combustion, favouring the char formation and thus are considered condensed-phase FRs [71,72]. 

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