Lipophilic Polyelectrolyte Gels and Crystal Crosslinking, New Methods for Supramolecular Control of Swelling and Collapsing of Polymer Gels

This review focuses on our trial to control the swelling and collapsing of polymer gels by two different approaches. One is the introduction of ion-pairs from bulky and hydrophobic ions into hydrophobic polymers to form ionic polymer gels as "lipophilic polyelectrolyte gels". Partial dissociation of these ion-pairs in nonpolar media, such as chloroform and THF, provides them a high swelling ability as superabsorbent polymers. Compatibility of the polymers with the media and ion dissociation are crucial for the superabsorbency. The other is preparation of polymer gels by controlling the size, shape and crosslinking points with the aid of nanoporous metal-organic frameworks (MOF). It includes polymerization between the organic ligands as host monomers fixed on the open framework and the guest monomers that penetrate into the nanopores. Thus, all the components in a crystal are polymerized, which is called "crystal crosslinking". Hydrolysis of the coordination bonds produces insoluble polymer gels without metal ions. The shapes of the polymer gels are essentially identical to those of the template crystals, and the swelling ability is controlled by arrangements of the host monomers in the template crystals. These two approaches should be unique and effective for controlling the swelling ability