Phase behavior of polymer/mosquito repellent system PLA/DEET
The phase diagram of the binary polymer/mosquito repellent system poly (lactic acid) (PLA) and N,N-diethyl-3-methylbenzamide (DEET) has been established for the purpose of screening the potential use of biodegradable PLA as drug-delivery reservoir for DEET. Crystallization-induced solid-liquid (S-L) phase separation occurs on sufficiently slow cooling of liquid solutions containing crystallizable PLA at temperatures slightly higher than ambient. Non-isothermal crystallization starts spherulitically at point-like nuclei, followed by dendritic crystal growth due to depletion of crystallizable polymer in the solution in the later stage. Analysis of vacuum-dried crystallized systems reveals the formation of intra-spherulitic scaffold-like structures with a pore size smaller than 10 μm. If crystallization is suppressed due to fast cooling or high concentration of stereodefects in racemic random PLA copolymers then liquid-liquid (L-L) phase separation into an almost pure DEET phase and a PLA/DEET solution occurs at temperatures slightly below room temperature .
 Sungkapreecha C, Iqbal N, Gohn AM, Focke WW, Androsch René, Phase behavior of the polymer/drug system PLA/DEET, Polymer (2017), doi:10.1016/j.polymer.2017.08.031
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