The effect of the preservative methylparaben on the thermoresponsive gelation behavior of aqueous solutions of poloxamer 407

The effects of 0.2% (w/v) methylparaben (0.2MP) on the micellization, intermicellar association and gelation characteristics of poloxamer 407 (PX) in aqueous solution as well as the water distribution in PX based samples have been investigated. Differential scanning calorimetry (DSC) studies demonstrated that 0.2MP shifted the critical micellization temperature (CMT) of PX to a lower temperature. According to sub-ambient DSC determination, 0.2MP disturbed interfacial water surrounding PX and decreased CMT. Flow curves revealed that intermicellar association of PX was promoted by 0.2MP. Since more intermicellar packing facilitated the thermoresponsive gelation, the reduction of the sol-gel transition temperature of PX was also substantiated in the presence of 0.2MP as indicated by temperature sweep tests.