Synthesis and formation mechanism of porous 2‐hydroxyethyl methacrylate–ethylene glycol dimethacrylate copolymer beads

Abstract

AbstractPorous 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.