Síntese assistida por micro-ondas e caracterização estrutural de novas resinas termorrígidas

Abstract

Benzoxazines are a relative recent class of high performance thermosetting resins. These benzo-heterocyclic compounds have been extensively studied and reviewed to scientific community due to their applications, especially in the fields of polymer chemistry and materials science. A limitation in the synthesis of benzoxazines is the duration of the reaction processes, where it normally takes several hours to obtain the desired products. The microwave-assisted organic synthesis (MAOS) is a well-established technique that has been used in the enhancement of chemical reactions. In this sense, this work aims to explore the versatility of microwave irradiation for a synthesis of new bio-based benzoxazines. The guaiacol, along with paraformaldehyde and different conjugated and non-conjugated amines are successfully fused into guaiacol-derived 3,4-dihydro-2H-1,3-benzoxazines. The reactions conducted under microwave irradiation are completed much faster than those under traditional heating, preserving or even improving, total yields. The chemical structures of novel benzoxazines are confirmed by 1H and 13C NMR spectroscopy, FT-IR, and HR-MS. The thermal behavior of the resins are evaluated by DSC and TGA, where it was observed that these compounds have good thermal stability and wide processing-window, with onset temperature of polymerization above 230 ˚C. These results indicate dramatic improvement over the traditional methodologies for the production of this class of resins. Therefore, MAOS can be considered a green and efficient strategy for the synthesis of eco-friendly benzoxazines.