Cross-Linked Poly(methacrylic acid-c o-poly(ethylene oxide) methyl ether methacrylate) Microspheres and Microgels Prepared by Precipitation Polymerization: A Morphology Study

We applied the concept of precipitation polymerization in organic solvents to the polar and hydrogen-bonding monomers methacrylic acid (MAA) and poly(ethylene glycol) methyl ether methacrylate (PEGMM), with ethylene dimethacrylate (EDMA) as cross-linker. Soluble copolymers, swellable microgels, microspheres, macrogels, and coagulum were observed after copolymerization in mixtures of methyl ethyl ketone and heptane. Increasing the amount of covalent cross-linker or decreasing the solvency of the reaction medium caused a change of morphology from microgels to microspheres. The ratio of acid to ethylene oxide groups present in the comonomers also dramatically changed the polymer−polymer interactions and hence the morphology. Three types of cross-linking are proposed to exist in this system: covalent cross-linking by EDMA and hydrogen-bonding cross-linking between two acid units as well as between acid and ethylene oxide groups. The size of the particles increased with decreasing solvency, decreasing EDMA concentration and increasing PEGMM concentration.