Robert J. DeVoe

Catalytic Opening of Lateral Benzoxazine Rings by Thiols

Publisher Summary Benzoxazines are easy and inexpensive to prepare via condensation of phenol, formaldehyde, and an amine. Some are commercially available and various mercaptans in a range of functionalities are also commercially available. Both are inexpensive. Benzoxazines (BZs), one of the COLBERT coreactants, have enjoyed a great deal of attention of late because of their excellent high temperature properties, low moisture uptake, lower cure shrinkage than epoxies, great dielectric properties, and so on. The COLBERT reaction affords a significant advance in lowering the polymerization temperature of benzoxazines. In particular, the reaction allows benzoxazine polymerization under ambient conditions, providing furthermore flexibilized and toughened polymers. In addition to its utility as a facile method to prepare thermoplastic and thermosetting condensation polymers possessing unique structural, thermal, moisture, and adhesive properties, the COLBERT reaction provides the simplest pathway to structural motifs useful as synthons for Sommelet–Hauser rearrangement. 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 catalyst or thiol. 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. The monomers used are inexpensive and commercially available from a variety of sources. The polymers can be prepared under ambient and solventless conditions, and have a variety of uses from adhesives to moisture barrier films. These considerations are encouraging for developing commercial applications for the COLBERT polymers.