Preparation and Characterization of Thermoresponsive Poly(N-isopropylacrylamide-co-acrylic acid) Hydrogels: Studies with Electroactive Probes

摘要

A new method of preparing thermoresponsive hydrogels consisting of N-isopropylacrylamide (NIPA) and acrylic acid (AA), with a weli-defined concentration of an elec-troactive probe, 1, 1’-ferrocenedimethanol (Fc(MeOH)2), is described, and a comparison of the physical and electrochemical properties of NIPA—AA gels with those of aqueous solutions is presented. The NIPA—AA gels undergo a discontinuous volume phase transition at 45 0C; this transition results in a release of approximately 40% of the solution mass from the gel phase. Character-ization of hydrogels with electroactive probes is performed using electroanalytical techniques and FTIR and UV/vis spectroscopies. Steady-state voltammetry and chrono-amperometry at platinum disk microelectrodes are used to measure the diffusion coefficient of Fc(MeOH)2 in gels under a wide range of experimental conditions. Similar diffusion coefficients for Fc(MeOH)a in NIPA-AA gels are obtained by either electroanalytical technique at temper-atures lower than 20 0C. The uncertainty in the Fc-(MeOH)2 concentration in the gels, resulting from the discontinuous volume cbange transition, necessitated the use of concentration-independent chronoamperometric data (i.e. the chronoainperometric response divided by the steady-state current obtained at sufficiently long times) to obtain reliable diffusion coefficient values for Fc-(MeOH)2. For temperatures above the volume phase transition, changes of concentration of Fc(MeOH)2 are detected in a copolymeric collapsed phase.