The COLBERT reaction follows a two-step acid-catalyzed nucleophilic addition mechanism. During the first step, the benzoxazine amine is protonated by either an acid catalystor thiol. That is immediately followed by the sulfide attack on the BZ-1 methylene carbon during which the carbonoxygen bond is severed and a new thioether bond is formed, resulting in the ring-opening of the benzoxazine. The reaction is fast and results in sufficiently high yields of product to routinely prepare linear COLBERT condensation polymers as well as cross-linked materials.