SYNTHESIS AND FORMATION MECHANISM OF POROUS 2-HYDROXYETHYL METHACRYLATE ETHYLENE-GLYCOL DIMETHACRYLATE COPOLYMER BEADS

Porous poly(2-hydroxyethyl methacrylate) (PHEMA) beads cross-linked with ethylene glycol dimethacrylate (EGDM) were prepared by the suspension polymerization of the monomers in the presence of cyclohexanol or toluene as the diluents. A 20% aqueous NaCl solution containing MgCl2 . 6H2O, bentonite, and gelatine was used as the water phase. In this way, spherical, highly swellable, and/or porous copolymer beads of sizes 0.1-1.0 mm could be synthesized at EGDM contents higher than 20 mol %. The copolymers formed in cyclohexanol, compared to those prepared in the absence of a diluent, exhibit a larger degree of volume swelling in water, indicating that most of the diluent remains in the gel phase throughout the copolymerization. Contrarily, toluene induces porous structures even at a very low degree of cross-linking (41% porosity at 2 mol % EGDM). An interesting feature of HEMA-EGDM copolymerization in toluene is that the pore volume of the networks increases with increasing EGDM concentration up to 20 mol %, but it decreases again as the EGDM concentration further increases. The results can be explained with the differences in the solvating conditions of the copolymers depending on their EGDM contents.