Spatially resolved solvent interaction with glassy HPMC polymers studied by magnetic resonance microscopy

Magnetic resonance microscopy was used to study the interaction of an alkaline water solvent (pH=12) with hydroxypropylmethyl cellulose (HPMC) matrices with different molecular masses Mw=12000, 86 000, and 120 000. The polymers in the form of cylinders were hydrated at 37 °C and monitored at equal time intervals with a 300 MHz Bruker AVANCE. The spatially resolved spin-spin relaxations times T2 and diffusion coefficients D of the solvent molecules within the gel layer of HPMC samples, along with changes in the dimension of the glass core of the polymers were determined as a function of hydration times. The experimental data allows us to characterize the diffusion mechanism as being Fickian and to determine the mean diffusivity values D¯ of the solvent molecules for each voxel within the gel of the studied polymers. The influence of the molecular mass of the HPMC polymers on swelling properties has been shown.