Three dimensional crosslinked networks of hydrophilic polymer chains where the free polymer segments are solvated by water constitute hydrogels. Some hydrogels contain groups which interaction with water depends strongly on external parameters (temperature, pH, ionic force). External stimuli induce coil to globule transition of the free rotation segments, inducing large diminution of volume. Therefore, it is said that the material react to external stimuli in a “smart” way and the materials are called smart hydrogels.
An extensive study of synthesis and properties of hydrogels, polymers which swell in water, has been performed. However, the study of analogous crosslinked polymers where the free rotation chains are solvated by nonaqueous solvents is quite limited. Moreover, while smart hydrogels have been extensively studied, there are no study of smart solvogels, that is materials swelled in solvents which react to external stimuli by large changes in the volume and other physicochemical properties.
In the present communication, crosslinked polyacrylamides are swelled in different solvents (alcohols, ketones, amides). The swelling degree and swelling rate depends on the solvation capability of the solvent on the polymer chains. Additionally, crosslinked polymers which show phase transition temperatures are synthesized.
The ability to swell the solvogels in good solvents for linear polymers allows synthesizing true semi-interpenetrated solvogels. Additionally, allows loading inside the solvogels active molecules (e.g. complexing agents) which, if the gel is now swelled in water, are retained inside the polymer matrix.
The swelling of polymeric gels in homogenous solvent mixtures show that, as happens with real solutions of small molecules, the solvation capability of the mixed solvents is not a linear relationship of that of the pure solvents. In the case of solvogels, this result suggests that the good solvent of the polymer chains is preferentially retained inside the solvogel. In that way, low temperature separation of miscible solvents could be performed. Smart solvogels could be used for the temperature driven release of molecules.
The possibility of synthesizing solvogels affected by other parameters (acidity, solvent activity) is also discussed.