Copolymerization and phase separation behaviors of benzoxazine–amine thermosets

The ring-opening addition reaction of benzoxazine with amines offers advantages in terms of curing temperature and control of material characteristics. In the present article, a benzoxazine monomer, 3,3′-sulfonyl-bis(4,1-phenylene)-bis(3,4-dihydro-2H-1,3-benzoxazine) (BZS), was synthesized from 4,4′-diaminodiphenyl sulfone (DDS), paraformaldehyde and phenol. The copolymerization and phase separation behaviors of BZS/DDS curing systems were studied. Experimental results show that there are competitive copolymerization paths in the curing process, and, moreover, that these copolymerization paths may result in phase separation in the cured resin. These findings can be used for improving polybenzoxazine properties such as toughening, and thus have potential value for various applications such as in the development of coatings, adhesives, and composites.