Effect of aromatic boronic acids on thermal characteristics of polybenzoxazine derivatives and composites

İpek, Halil
Polybenzoxazines, a class of phenolics offering excellent mechanical and physical properties, have been developed to overcome the shortcomings of the traditional phenolic resins. These materials possess low water absorption, low melt viscosity, near-zero shrinkage upon curing and releasing no by-products. In addition, molecular design flexibility of benzoxazine monomers gives opportunity to adjust the properties of the polybenzoxazines according to the application area making them advantageous for various industrial and academic applications. Several methods such as preparation of alloys with other high performance polymers, hybridization with inorganics, designing of novel monomers and incorporation of additive compounds during curing process were employed to improve the performance of polybenzoxazines. In this work, polybenzoxazines and polybenzoxazine composites involving aromatic boronic acid derivatives were prepared to improve thermal characteristics. The effect of aromatic boronic acids on thermal characteristics of polybenzoxazines were investigated. In the first part, benzoxazines based on phenol and aniline or/and 3-amino phenyl boronic acid were synthesized. The monomers were polymerized by using optimized curing program. In the second part, benzoxazine monomer based on phenol and 4-aminomethyl benzoate was synthesized. The monomer was cured with and without incorporation of various amounts of aromatic boronic acids (benzene-1,4-diboronic acid, 4,4′-biphenyldiboronic acid, or 3-hydroxyphenylboronic acid). The structural and thermal characteristics of the benzoxazine monomers, polybenzoxazines and polybenzoxazine composites were analyzed by NMR, FTIR, DSC, TGA and DP-MS techniques. Improvement in the thermal characteristics were recorded by the incorporation of aromatic boronic acids either as an additive or as a reactant for the synthesis of the benzoxazine monomers.