Synthesis and characterization of oligo(phenoxy-imine)s of Schiff bases containing phenyl-1,3,5-triazine unit: limit oxygen index values of oligomers

Abstract

Aromatic compounds containing hydroxyl groups in their structure are converted to oligomer or polymer products from the combination of phenoxy-structured radical units in the presence of oxidants such as O₂, H₂O₂ and NaOCl in alkaline or acidic aqueous media. These macromolecule compounds are used in many fields in industry because they contain both phenyl units and different functional groups in their structures. Since the phenyl units in the main chain give rigidity to the structure, the thermal stabilities of these types of polymers are quite good. Schiff base compounds were obtained as a result of the condensation reaction of 4-hydroxy-3-methoxybenzaldehyde, 2-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 5-bromsalicylaldehyde and 2-hydroxy-1-naphthaldehyde compounds with 2,4-diamino-6-phenyl-1,3,5-triazine as amine. Oligo(phenoxy-imine)s were synthesized from Schiff bases by oxidative polycondensation in the presence of O₂ oxidant in aqueous alkaline medium. The structural characterizations of Schiff bases and oligo(phenoxy-imine)s were performed by FT-IR, ¹H-NMR, ¹³C-NMR and UV–Vis analyses. Electrochemical band gap (\(E^{\prime}_{g}\)) values of monomers and oligomers were calculated from CV measurements. The \(E^{\prime}_{g}\) values of FMD, FMB, FMM, FMF, FMN, OFMD, P-FMB, OFMM, OFMF and OFMN were calculated to be 2.80, 2.63, 2.52, 2.76, 2.12, 2.57, 2.49, 2.44, 2.51 and 2.07 eV, respectively. Limit oxygen index values of OFMD, P-FMB, OFMM, OFMF and OFMN were calculated to be 33.46%, 38.85%, 38.43%, 44.86% and 23.46%, respectively. Also, the molecular weight distributions, glass transition temperature (T_g) and surface images of oligomers were determined from GPC, DSC and SEM measurements, respectively.