Polybenzoxazines as Self-Healing Materials

The present chapter deals with the synthetic pathways for obtaining self-healing materials based on benzoxazine chemistry. Several strategies for self-healing systems involving the use of polybenzoxazine precursors as healing additives are presented. In the first approach, the additive poly(BA-dah)main contained in polysulfone (PSU) films were shown to faintly undergo a thermal ring opening reaction. Thus, thermal treatment at 160°C enables poly(BA-dah)main to chemically bind to PSU chains and form networks through the Friedel-Crafts reaction, demonstrating a novel self-healing behavior. In the second strategy, a self-healing behavior of poly(propylene oxide)s bearing coumarine-benzoxazine units (poly(Cou-PPOa)tele) through light induced coumarine dimerization reactions is described. Four different types of poly(propylene oxide) amines with molecular weights ranging from 440 to 5000 Da were reacted with formaldehyde and 4-methyl-7-hydroxycoumarin to yield desired polymers. The photo induced healing of the cured films was proven by UV-Vis spectral investigations. It was demonstrated that the toughness of the films were improved by employing allyl benzoxazine (P-ala) in the self-healable film formulation. Additional self-healing strategies for the poly(propylene oxide)s bearing benzoxazine units poly(BA-PPOa)main through supramolecular attractions are also described. The cross-linked polymer films from poly(BA-PPOa)main and additive carboxylic acid containing benzoxazine monomer (P-aba) showed autonomous self-healing capacity through the supramolecular interactions.