Poly(divinylbenzene) microspheres as an intermediate morphology between microgel, macrogel, and coagulum in cross-linking precipitation polymerization

Precipitation copolymerizations of mixtures of divinylbenzene-55 (DVB55) an d 4-methyl-styrene at total monomer loadings of 4 vol % were conducted in s olvent mixtures comprised of mixtures of methyl ethyl ketone and heptane. T he experimental compositions hence formed a two-dimensional matrix where th e actual DVB content varied from 0 to 55% and the solvent composition varie d from 0 to 100 vol % MEK. Four distinct polymer morphologies including mic rospheres, microgels land soluble polymer), macrogel, and coagulum were obs erved and are reported in form of a morphology map superimposed on the abov e compositional map. The structures of these four polymer architectures are described, and the effects of both DVB concentration and solvency on the t ransitions between morphology domains are discussed. The portion of reactio n volume occupied by the polymer formed decreases with both decreasing solv ency and increasing DVB concentration. These results indicate that the micr ospheres are formed, in part, by an internal contraction which is caused by both the marginal solvency of the continuous phase and the cross-linking o f the polymer network. This contraction is likely progressive, supporting t he presence of a lightly cross-linked corona around the microspheres which acts as an insitu steric stabilizer layer.