Estudo teórico das reações de eletropolimerização dos ácidos 3- hidroxifenilacético e 3-hidroxibenzóico e caracterização experimental do poli (ácido-3-hidroxibenzóico)

Abstract

This work reports the theoretical study of the mechanism of polymerization of 3-hydroxyphenylacetic acids (3-HPA) and 3-hydroxybenzoic acid (3-HBA) and characterization of polymeric material obtained in the electropolymerization of 3-HBA.From the molecular modeling of 3-HPA and intermediates, analysis of the properties derived from the electronic structure, it was possible to propose a mechanism for the electropolymerization reaction. Carbon-6 presents the higher increase in the amount of partial charge, through the processes of 3-HPA oxidation to form cr3-HPA deprotonation followed by this lead to the r3-HPA. The pairing should occur between the SOMO beta of cr3-HPA and SOMO alpha r3-HPA forming the ether bond observed in the experimental IR. We also investigated the electropolymerization of 3-HBA in three different pH values (0.5, 7.0, 12), and you can see that in an acid medium the formation of electrochemically active material is more evident. The study of electrical properties by cyclic voltammetry utlize cationic and anionic probes revealed that the film formed has anionic structure. The 3-HBA and poly (3-HBA) were characterized by spectroscopic techniques (FTIR, UV/Vis, fluorescence), thermal analysis (TGA and DTA) and structural analysis (DRX and MEV). The FTIR spectra showed that the functional groups are preserved in the polymer structure and also highlights the emergence of the ether group in the polymer structure. The analysis of UV/Vis revealed a band broadening and increased extent of absorption of the polymer in the visible region, indicating the extent of conjugation in the polymer structure. The diffractograms obtained for the monomer and polymer are characteristic of crystalline structures. Based on the studies of the electronic structure of 3-HBA and intermediaries, a mechanism for the electropolymerization reaction was proposed, in which the carbon 6, similarly to 3-HPA, should be attacked and the pairing should occur between the SOMO beta of cr3-HBA with the SOMO alpha r3-HBA, the lower energy gap, forming a polyether as elucidated in the FTIR spectra. The propagation of the reaction occurs through the pairing of radicals from the oxidation and deprotonation of the monomer with cation radicals from oxidation of the oligomers formed.