SYNOPSISSuspended emulsion is a new polymerization process in which a water phase containing the initiator is suspended in an organic phase containing the monomer; the polymer formed is insoluble in both the organic and water phases. The final morphology of the polymer is a powder of grains (around 100-300 microns) formed with agglomerates of primary particles (around 1 micron). This article describes the effects of small amounts of either suspending agents (water-soluble polymers) or surfactants. These effects concern mainly the morphology (grain and particle size), but also the polymerization kinetics. A rather homogeneous distribution of grains and particles inside the grain may be obtained by using a cellulosic polymer as the suspending agent and an anionic surfactant such as sodium dodecyl sulfate.
I NTRO DUCT10 NPoly(viny1 chloride) (PVC) is an important commodity polymer that is prepared industrially in huge amounts, using various radical polymerization processes. The main process is suspension polymerization using water-soluble polymers such as cellulosic derivatives or poly (vinyl alcohol) as suspending agents, which stabilize first the monomer droplets of the organic phase dispersed through efficient stirring and, later on, the polymer grains; a bulk precipitation polymerization takes place inside the monomer droplets. According to the adopted nomenclature, microdomains (10-20 nm in size) are formed under precipitation and a first aggregation step of the growing polymer chains. These microdomains soon undergo a second aggregation step to give primary particles ( 100 nm initially). During the polymerization, these primary particles are growing in size and further give agglomerates inside the grains. A skin of the suspending agent grafted with PVC is formed around the grains (size 50-300 * To whom correspondence should be addressed. CCC 0021-8995/94/131879-11 microns). The final grains are more or less porous, according to the polymerization conversion (density difference between the polymer 1.42 and the monomer 0.86) , the interfacial tension of the suspending agent system ( hydrophilicity of the water-soluble polymer, presence of other nonionic or ionic surfactants), and the aggregation modes of the primary particles (modulated by the stirring mode and intensity, the presence of surfactants, the temperature, etc.) . The second important process for commodity polymers is the bulk process, which can lead to the same kind of morphology with microdomains, primary particles, and grains of about the same sizes. The grains are not stabilized by any surfactant; however, their external surface is formed with agglomerates of primary particles more compact than those present inside these grains. The compactness of that skin has probably a mechanical origin upon collision of the grains with other grains under the high stirring conditions experienced by the system in the initial (up to 10% conversion) steps of the process. The internal morphology is comparable with that of the suspension process, the final porosity...
