Investigation of translational motion of poly(ethylene glycol) macromolecules in poly(methacrylic acid) hydrogels

The translational mobility of linear macromolecules of poly(ethylene glycol ) (PEG) within a weakly cross-linked poly(methacrylic acid) (PMAA) hydrogel was investigated by means of the pulse field gradient (PFG) NMR method in order to reveal the effect of PMAA/PEG complex formation. It was found that inside the collapsed gel a fraction of the PEG molecules has self-diffusio n characteristics like those of the network chains. This suggests the forma tion of an interpolymer complex, as a result of which some linear molecules acquired the dynamic properties of the network chains. Another fraction of the PEG macromolecules inside the collapsed gel enjoyed free diffusion, fo r they were not included in the complex with PMAA. In contrast, within the swollen gel (at concentrations of PEG higher than 5 wt.-%) the self-diffusi on coefficient of all PEG molecules was independent of the diffusion time, which indicates an absence of the interpolymer complex (or at least that it s lifetime is negligibly short).