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An experimental and modeling study was carried out to understand the relationship between the viscosity of a multimodal latex and its particle-size distribution (PSD) and polymer concentration. This study illustrates the inadequacy of existing models in predicting the viscosity of complex latices. It is shown that the latex viscosity at a fixed shear rate is very sensitive to the polymer concentration at high solids content and to the PSD.

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Aqueous dispersions of polystyrene latexes encapsulating a copper phthalocyanine blue pigment were formulated using the miniemulsion polymerization technique. The organic pigment was first suspended into the monomer phase, and the resulting oily suspension was subsequently converted into stable miniemulsion droplets using various types and concentrations of hydrophobe (costabilizer). The pigmented monomer emulsions were finally polymerized using potassium persulfate as the initiator. It was shown that the organic pigment could stabilize the miniemulsion droplets, and be thus satisfactorily encapsulated without introducing any other compound in the formulation. In a subsequent approach, the stability of the miniemulsion droplets was improved by using either hexadecane, hexadecanol or a polystyrene prepolymer as the hydrophobe. Dynamic light scattering and transmission electron microscopy measurements showed that the size and the morphology of the resulting pigmented polymer particles were greatly influenced by the presence of the costabilizer.© 2003 Society of Chemical Industry

A Lewis acid surfactant combined catalyst (LASC) was tentatively used in a cationic polymerization in miniemulsion of p-methoxystyrene (pMOS). In a first part, the initiating potential of trisdodecyl sulfate ytterbium (Yb(DS)3, 0.25H2O) was evidenced in the solution polymerization of pMOS initiated by the corresponding chlorinated adduct pMOS-HCl. Miniemulsion polymerizations of pMOS performed using the same initiating system gave rise to oligomers, but experimental conditions chosen could not evidence the expected LASC-mediated cationic polymerization process. Further studies showed that LASC is located at the interface and acts only as a surfactant together with SDS. The polymerization occurred due to the hydrolysis of pMOS-HCl. The resulting acidification of the water phase leads to the transformation of SDS into its sulfuric acid form acting as an inisurf according to an interfacial cationic polymerization process. Latex particles of pMOS incorporating narrowly distributed low molar mass chains were obtained.

A poly(ethylene oxide)-based macromolecular agent for reversible addition-fragmentation chain transfer (PEO-RAFT, 2 000 g • mol -1 ) was synthesized and used as a stabilizer and a control agent in the miniemulsion polymerization of styrene. Using 2,2′-azobis(isobutyronitrile) as initiator, stable polystyrene (PS) particles sterically stabilized by the PEO segments were obtained with almost complete conversion after 22 h. Molar masses increased linearly with conversion although rather broad molar mass distributions were obtained due to the presence of several populations of PEO-b-PS block copolymers. However, dynamic light scattering analyses showed a significant increase in particle diameter with conversion and the ratio of the number of particles to the number of droplets (N p /N d ) was thus lower than one indicating that the system did not follow a true miniemulsion process. Transmission electron microscopy additionally revealed the presence of holes inside the formed particles suggesting that block copolymer PEO-b-PS could be buried inside the particles during the polymerization. Varying the concentration and the nature of the initiator did not lead to an improvement of the molar mass distribution, while a decrease in polymerization temperature to 40 °C enabled to keep the particle size constant throughout the polymerization with values close to the starting droplet diameter as expected for a true miniemulsion.

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