Synthetic hydrogels. Part 9—Preparation and characterisation of macroporous hydrophilic matrices

Abstract

The photopolymerisation of solidified hydrophilic monomers around frozen ice crystals to produce macroporous matrices is described. This technique enables a range of hydrophilic materials to be produced in which the transport and sorption properties are not simply related to fractional hydration, as is the case in conventional hydrogels. The essential requirement for their production is the choice of a monomer/solvent system in which rapid cooling produces crystallisation of the solvent without phase separation of the monomers. A study of the phase equilibria involving hydrophilic monomers, in conjunction with water and ethyene glycol as the solvent phase, identifies the composition ranges that enable this ‘freeze–thaw’ polymerisation to be successfully accomplished. The principle can be utilised to prepare membranes or particulates with morphologies based on interconnected pores of diameter in the range 1–20 µm. Careful choice of monomers, solvent, crosslinking agents and polymerisation conditions leads to variable and controlled distributions of pore sizes.