Synthesis, Characterization and Thermal Properties of New and Known 1,3-Benzo- and Naphtho-Oxazine Monomers Obtained Using a Modified Step-wise Procedure

Abstract

New and known 1, 3-benzo- and naphtho- oxazine monomers were synthesized using a modified step-wise procedure in which formaldehyde which is a suspected human carcinogen and a confirmed animal carcinogen was replaced with methylene bromide for ring-closure reaction. Salicylaldehyde and 2-hydroxy-1-naphthaldehyde were separately condensed with the primary aromatic amines p-toluidine, p-phenylenediamine and 4-butylaniline to give imine compounds which on reduction with NaBH4 yields 2-hydrobenzylamines / 2-hydroxynaphthylamines depending on the 2-hydroxyaldehyde used. The 2-hydroxybenzylamines / 2-hydroxynaphthylamines subsequently undergo ring-closure reaction with methylene bromide in absolute alcohol to give 1, 3-benzoxazine and naphthoxazine monomers in good yields. The chemical structures of the synthesized compounds were confirmed using FT-IR, 1H and 13C NMR spectral analysis and mass spectrometry (GC-MS). The thermal properties of the synthesized compounds were determined using Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). From the result of thermal analysis, it may be concluded that the bifunctional monomers show higher glass transition temperature (Tg) and better thermal stability than the monofunctional monomers.