Monoolein cubic phases containing hydrophobically modified poly(N-isopropylacrylamide)

Monoolein (MO) cubic phases containing a hydrophobically modified poly(N-isopropylacrylamide) (PNIPAM) were prepared by hydrating MO using the polymer solution. A copolymer of N-isopropylacrylamide and octadecylacrylate [P(NIPAM-omega-ODA)] was prepared as a hydrophobically modified PNIPAM; it included the cubic phase so that the content was 0.17%. The copolymer was identified by Fourier transform infrared (FTIR) and proton NMR spectra. The lower critical solution temperature (LCST) of the polymer was found to be 30 similar to 32 degrees C through differential scanning calorimetry (DSC). At the air/water interface, hydrophobically modified PNIPAM was more surface-active than homo-PNIPAM, possibly due to the hydrophobic ODA moiety. On the other hand, the phase transition of the cubic phase-containing PNIPAM was investigated on a polarizing microscope, and the phase transition temperature was determined using DSC. Its values of ca. 70 degrees C is characteristic of the MO cubic phase. Sodium salicylate was included in water channels of the cubic phase and the degree of release was observed for 4 days at 20 and 40 degrees C. A higher temperature resulted in a higher degree of release. Under our experimental conditions, it is believed that the higher release was not due to thermal contraction of the polymer, but to the thermally enhanced diffusion of sodium salicylate.