TG/DSC/FTIR studies on the oxidative decomposition of polymer-silica composites loaded with sodium ibuprofen

The purpose of this study was to investigate the thermal properties of polymeric microspheres and their modified with drug molecules and silica gel counterparts under oxidative atmosphere. Permanently porous polymeric microspheres of poly(TRIM) (trimethylolpropane trimethacrylate) and poly(HEMA-co-TRIM) (2-hydroxyethyl methacrylate) were synthesized via the suspension-emulsion polymerization method. The polymer-sodium ibuprofen (IBS) solid dispersions were prepared by the solvent diffusion method. The ternary polymer-sodium ibuprofen-silica gel composites were obtained by hydrolysis and condensation of silica precursor (tetraethoxysilane, TEOS) introduced into the solid dispersions. The acidic and basic environments of TEOS gellation were used, so the acid (A) and base (B) sets of ternary composites were produced. The conducted TG/DSC/FTIR analyses reveal that thermal decomposition of pure polymers starts at about 240 °C with degradation of methacrylate linear units in accordance with the depolymerization mechanism which is accompanied by the oxidation process of methacrylate ester bonds. The next maxima of degradation of pure organic matrices are observed at about 360 °C, 430 °C and 510 °C and are connected with oxidation processes. The thermal stability of solid dispersions of the drug within polymeric matrices as well as ternary composites is higher at about 90 °C in comparison with pure organic matrices. Drug molecules and silica spices act as a shield preserving both the transfer of air inside the structure of the studied materials and the evaporation of gases produced as a result of thermal decomposition of the organic phase.