Dispersion polymerization of styrene in polar solvents. IV. Solvency control of particle size from hydroxypropyl cellulose stabilized polymerizations

Abstract

AbstractChanging solvent has a dramatic effect on the outcome of HPC stabilized dispersion polymerization of styrene in polar solvents. In methoxyethanol/ethanol mixtures, particle size varies from essentially infinity for unstabilized reactions (below 30% ethanol) to about 3 microns in ethanol. In a series of n‐alcohols, there was a maximum in particle size at intermediate chain length: particle size increased from 2 microns in methanol to 8.3 microns in pentanol, then decreased again to 1 micron in octadecanol. These results were rationalized in terms of the three‐component Hansen solubility parameters. The largest particles were obtained in solvents with Hanson polarity and hydrogen bonding terms closest to HPC. The generality of the three‐component solubility parameter approach was examined by reactions performed in eight mixed solvents with the same values of all three Hansen terms. Seven of the eight solvents gave particles of similar size and molecular weight. The two critical effects of solvent on both particle size and molecular weight appear to be: (a) the solubility properties of the grafted HPC‐PS formed, and (b) the partitioning of monomer and initiator between solution and particle phases subsequent to nucleation.