Exploring the chemical structure of polydapsone

Abstract

Polydapsone is a promising polymer that has been prepared mainly as copolymers. Due to the similarity of dapsone monomer to aniline, its polymerization has been carried out in the same conditions as in the synthesis of polyaniline, but unlike this one, polydapsone chemical structure and properties are still not fully known. In this paper, polydapsone was synthesized by oxidative polymerization in an aqueous HCl medium, using ammonium persulfate as the oxidizer agent. It was observed that carrying the synthesis both at room temperature and for 48 h resulted in higher yields than at 5 °C or for 24 h. The molar ratio of dapsone:oxidant also increased the reaction yield with the increase in oxidant content, and the stoichiometric ratio of 1:4 led to the best results. Fourier transform infrared and Raman spectroscopies summed to density functional theory calculations revealed that the polymerization of dapsone occurs via amino-amino coupling with the formation of protonated amines and that the Cl− counterions take part in the structure. Ultraviolet spectroscopy showed no significant differences between the monomer and the polymer, suggesting that polydapsone has a semiconductor character. X-ray diffraction revealed a semicrystalline morphology that appears only when the polymer is in its protonated form, at the same time that its thermal stability increases with deprotonation, as shown by thermal analysis. This approach allowed us to suggest a chemical structure for polydapsone and correlate the synthesis parameters with the chemical and crystalline structures and further with some physicochemical properties.