Lightly Cross-Linked Microgels by Precipitation Polymerization of Maleic Anhydride and Styrenic Monomers

The synthesis and properties of micron-sized particles by precipitation polymerization of maleic anhydride (MAn), styrene (Sty), 4-methylstyrene (4MS), and divinylbenzene (DVB-55) in methylethylketone (MEK)/heptane cosolvent mixtures are described. Particles were narrowly dispersed with diameters varying as a function of reaction solvent, cross-linker type and loading, and 4MS/Sty ratios. Diameters ranged from 1 to 14 μm when swollen in good organic solvents, with the largest sizes observed at low cross-linker loadings and for polymerization solvents containing ≥70 vol % MEK. At constant cross-linker loading and solvency, increasing the 4MS/Sty ratio from 0.1 to 1 more than doubled the particle diameters, illustrating the impact of comonomer composition on particle nucleation. Switching entirely from 4MS to Sty shifted solvency requirements for microgel formation by 10 vol % of the good solvent, MEK. Similarly, replacing DVB-55 with a diacrylate cross-linker restricted microgel formation to lower solvency regimes. Hydrolysis of anhydride groups gave microgels with pH-dependent swelling and volume swelling ratios of up to 40 depending on the degree of cross-linking.