Precipitation polymerization in acetic acid: study of the solvent effect on the morphology of poly(divinylbenzene).

This paper reports on two important results regarding the precipitation polymerization of poly(divinylbenzene) (PDVB) in acetic acid (HAc). (1) Acetic acid is a novel kind of solvent worthy of investigation because it is amphipathic and innoxious. Thus, two kinds of model solvents, methyl ethyl ketone (MEK) and n-heptane, were selected to investigate the solvent effect on the particle morphology of PDVB-55 during precipitation polymerization in acetic acid. Monodisperse PDVB-55 microspheres were obtained with an MEK content of 30 vol % and a DVB loading of 2 vol %. Odd-shaped particles were found to almost disappear when MEK was added. For MEK contents up to 90 vol %, space-filling macrogels consisting of small particles with diameters of around 10 nm were obtained. More homocoagulated particles were produced when n-heptane was added, for which concentrations up to 50 vol % gave rise to cauliflower-like particles. Thus, in the acetic acid system, microspheres, pumpkin-like particles, macrogels, and coagulum could be successfully obtained. (2) The preparation of nonpolar PDVB-55 particles could be more predictable. For the first time-based on the regulation of former studies--the regularity of the dispersive term (delta(d)) on the particle morphology for a PDVB precipitation polymerization system was reported. The three-dimensional Hansen solubility parameters were utilized to perfect the regularity of the Hildebrand solubility parameter. Microspheres or particles were formed in the range of moderate delta values for both parameters, i.e., delta = 20.2-24.3 MPa1/2 or delta = 16 MPa1/2. What was even more important, delta(d) was found to be around 15.4 MPa1/2, and delta(h) should be below 13.5 MPa1/2. Cyclohexane, cyclohexanone, n-butyl acetate, and 1,4-dioxane were used to verify this regularity, and positive results were obtained. Stable, uniform, and well-separated PDVB-55 microspheres and particles were produced as a result of interaction forces between oligomers, polymers, and solvent.