Synthesis and characterisation of cycloaliphatic and aromatic amines based cardanol benzoxazines: A comparative study

Abstract

In the current study, an attempt has been made to synthesize cardanol-based mono, bi, and tetra-functional benzoxazines by reacting various aryl amines and cycloaliphatic amines with cardanol (C) in the presence of paraformaldehyde under suitable experimental conditions by Mannich condensation. The resultant benzoxazines were characterized using several analytical techniques for their molecular structure, curing behavior, thermal stability, and hydrophobic nature. By using FTIR and 1H-NMR spectroscopic methods, the structure of benzoxazines was ascertained and assessed with benzoxazines based on aryl and cycloaliphatic amines. Using the DSC technique, the curing temperature of benzoxazines was investigated. Tetra-functional benzoxazines have a lower curing temperature than that of other mono- and bi-functional benzoxazines from the various systems of benzoxazines studied. It was also observed that the curing temperature of cycloaliphatic amine-based benzoxazines is also lower than that of aryl amine-based benzoxazines. The low temperature cure behavior of cycloaliphatic amine benzoxazine systems is due to the presence of a tertiary amine group, which contributes to a more basic nature than that of aryl amines. Thermal stability of polybenzoxazines was studied by TGA technique, among the different benzoxazine systems, the poly(C-ap-ddm) has higher char yield (30%) at 850 °C than that of other polybenzoxazines (poly(C-cha), poly(C-a), poly(C-mbch), poly(C-ddm), poly(C-ap-ipda), poly(C-ap-xyda) and poly(C-ap-mbch)). The value of water contact angle of cycloaliphatic amine-based benzoxazineswas found to be higher than that of aryl amines. Among the polybenzoxazines studied, poly(C-ap-mbch) possesses a higher value of water contact angle of 143°. Poly(C-aP-mbch) filled with 10 wt% SBA-15 (Santa Barbara Amorphous-15) possesses a value of lower dielectric constant (1.62) than that of poly(C-aP-ddm) (1.65). Data from different studies, cardanol based tetra functional benzoxazines can be used as sealants, encapsulants, adhesives, and matrices for microelectronics and automotive applications.