Structure–Property\nRelationship of Diaminodiphenylmethane-Based\nBenzoxazinesPrecursors for High-Performance Thermoset Polymers

A series of benzoxazine monomers were synthesized based\non 3,3′-,\n3,4′-, and 4,4′-diaminodiphenylmethane and salicylic\naldehyde (P-3,3′-d, P-3,4′-d, and P-4,4′-d, respectively)\nin order to identify the influence of the position of the amino group\nin an aromatic amine on the ability of the monomer to polymerize,\non its behavior during the polymerization process, and on the structure\nand properties of the polymers [poly(P-3,3′-d), poly(P-3,4′-d),\nand poly(P-4,4′-d), respectively] formed during their curing.\nThe chemical structure of all obtained benzoxazines was characterized\nusing <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy. Differential\nscanning calorimetry was used to study the curing process of benzoxazines\nas well as to determine the glass transition temperature of polymers\nbased on them. The thermal stability of each polymer was studied by\nusing thermogravimetric analysis. It was found that P-3,3′-d\nhas the lowest melting point and the highest glass transition temperature\nfor poly(P-3,3′-d), and the position of the amino group in\nthe initial diamine does not affect the onset of the polymerization\nprocess in the studied benzoxazines. The resulting compounds can be\nused as components of resins for polymer matrix composites with improved\nproperties.