Effect of phenol substitution on the network structure and properties of linear aliphatic diamine-based benzoxazines

A series of aliphatic diamine-based benzoxazines with different phenolic substitutions have been synthesized and characterized. Molecular structure of the monomers is verified by ¹H and ¹³C NMR, FTIR, and elemental analysis. The site of polymerization is regiospecified and the type of linkage in the network structure is manipulated by selectively blocking the ortho, para, and meta positions in the aromatic rings of the monomer. The controlled network structures and their properties are compared to those formed by the polymerization of aliphatic diamine-based benzoxazines prepared from unsubstituted phenol in order to provide insight into their structures. Investigation on the melting point, polymerization kinetics, gelation, and T_g and sub-T_g thermal transition is all reported on these systematically controlled structure polybenzoxazines.