ABSTRACT
Polymer hydrogels are cross-linked materials absorbing large quantities of water without dissolving. The ability of hydrogels to absorb water arises from their hydrophilic functional groups attached to the polymer backbone while their resistance to dissolution arises from cross-links between network chains (Tanaka 1981; Shibayama and Tanaka 1993). If such a conventional hydrogel is dried by heating, the polymer network obtained has no voids (pores) in its structure. However, as the polymer network swells again in water, the space between the network chains increases so that a type of porosity called molecular porosity appears. Thus, molecular porosity in conventional gels depends on the degree of swelling and the distance between the polymer regions is in the range of a few nanometers. In contrast, however, macroporous hydrogels refer to materials having a permanent porous structure that persist even in the dry state (Dusek 1982). According to the IUPAC, material having pores of larger than 50 nm are called macroporous (Sing et al. 1985). Some researchers dene macroporous gels as opaque materials with a measurable specic surface area and absorbing nonsolvents in their dry states (Millar et al. 1963; Rabelo and Coutinho 1994).
