Purpose: Glass transition temperature (T(g)) measurements of polymers are conventionally conducted in the dry state with little attention to the environment they are designed to work in. Our aim was to develop the novel use of dynamic mechanical analysis (DMA) to measure the T(g) of enteric polymethacrylic acid methylmethacrylate (Eudragit L and S) polymer films formulated with a range of plasticizers in the dry and wet (while immersed in simulated gastric media) states.
Methods: Polymer films were fabricated with and without different plasticizers (triacetin, acetyl triethyl citrate, triethyl citrate, polyethylene glycol, propylene glycol, dibutyl phthalate, dibutyl sebacate). T(g) was measured by a dynamic oscillating force with simultaneous heating at 1 °C/min. This was conducted on films in the dry state and while immersed in 0.1M HCl to simulate the pH environment in the stomach.
Results: The T(g) of unplasticized Eudragit L and S films in the dry state was measured to be 150 and 120 °C, respectively. These values were drastically reduced in the wet state to 20 and 71 °C for Eudragit L and S films, respectively. The plasticized films showed similar falls in T(g) in the wet state. The fall in T(g) of Eudragit L films to below body temperature will have far-reaching implications on polymer functionality and drug release.
Conclusions: Immersion DMA provides a robust method for measuring T(g) of polymer films in the wet state. This allows better prediction of polymer behaviour in vivo.
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