Abstract
This study compares the thermal stability of solid dispersions of indomethacin (IMC) in polyvinylpyrrolidone (PVP) at the 1:1, 7:1, 10:1, and 20:1 molar ratios of PVP to IMC. It is found that the thermal stability of IMC increases with increasing the amount of PVP as evidenced by increasing the decomposition temperature evaluated by thermogravimetry. The effect reaches its saturation for the 10:1 dispersion. The decomposition data are treated by isoconversional kinetic analysis that reveals that the thermal stabilization is associated with deceleration of the process. It also reveals that the mechanism of stabilization depends on the amount of PVP. In the 1:1 and 7:1 systems thermal stabilization is accomplished by an increase in the activation energy, whereas in the 10:1 and 20:1 systems it is associated with a decrease in the preexponential factor. Molecular level interpretation of these effects is proposed. The decelerating effect of PVP is also confirmed by comparing the rate constants.
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