The purpose of the present study was to propose a new approach for the characterization of insoluble amphiphilic copolymers using their emulsifying properties. The capacity of four newly-synthesized block copolymers to stabilize a model emulsion formed by mixing equal volumes of water and ethyl acetate was investigated. The copolymers were composed of dextran or heparin and poly(isobutylcyanoacrylate) and were obtained either by anionic or by radical polymerization of isobutylcyanoacrylate in emulsion, initiated on dextran or heparin. A quantitative analysis of the stability of the emulsion obtained with the different copolymers was evaluated using a Turbiscan MA 2000. The results suggested that this approach provides a new methodology for investigating emulsifying properties of polymers that are insoluble in pure solvents, allowing quantitative comparisons to be made between them. 相似文献
The morphology of polybutylacrylate–polystyrene (PBA–PS) core-shell latex particles prepared by seeded emulsion polymerization was investigated as a function of the addition method of styrene (St). The thin layer chromatography/flame ionization detector (TLC–FID) technique was used to characterize the morphology of the core-shell latexes. It was found that grafting PS to the PBA core occurs during seeded emulsion polymerization. The percentage of grafting depended on the method of addition of St, being greatest for the batch reaction, less for the preswollen batch reaction, and least for the semibatch reaction. Upon aging the PBA core-polymer migrated out of the latex particles with a low degree of grafting to form dumbellshaped particles, whereas the PBA–PS core-shell particles with a high degree of grafting remained spherical because of the emulsifying ability of graft copolymer. 相似文献
The polymerization of vinyl stearate in aqueous emulsions with a non-ionic emulsifying agent and potassium peroxydisulfate as initiator has been investigated by use of a dilatometric method to follow the reaction. In general, the reaction kinetics do not follow the pattern established for styrene. Variation of initiator concentration produced latices containing approximately equal numbers of latex particles, even though the rate of reaction was almost directly proportional to the peroxydisulfate concentration. For a given initiator and monomer concentration polymerization occurs very slowly when the monomer is completely solubilized but as the number of micelles is reduced and the number of emulsion droplets increased, the rate increases to an optimum value, whereafter it decreases. A mechanism is proposed by which the sparsely soluble vinyl stearate reacts and redistributes itself into latex particles of a different size range from the micelles and emulsion droplets originally present. 相似文献
Excellent stability of water-in-oil emulsions could be obtained by partial crosslinking of the fatty chain in several polyglycerol fatty esters. Such products were capable of emulsifying and stabilizing up to 50 wt% water in vegetable oils at a level of 3-5% emulsifier per total emulsion weight. The corresponding non-crosslinked products require at least 20-25% emulsifier to give the sane level of stability, with much higher viscosity. Degree of polymerization, molecular weight distribution, viscosity, dielectric constant and refractive index of the emulsifier were correlated to the emulsion stability. The most remarkable result is a clear correlation between the molecular weight of the emulsifier and emulsion stability; best emulsions were prepared with polymeric emulsifier with MW of Ca. 40000. 相似文献
Summary: This article deals with recent progress including the authors' work concerning the application of block copolymers as polymeric surfactants in heterophase polymerizations. The synthesis methods for preparing block copolymers by emulsion and dispersion techniques are outlined, with emphasis on recently developed controlled free radical polymerizations in aqueous media. Specific characteristics of amphiphilic block copolymers are described, for example, micellization and emulsifying effects. A general overview of emulsion and dispersion polymerization in an aqueous and organic medium with ionic and nonionic block copolymers is presented for the preparation of electrosteric and sterically stabilized latex particles. Typical examples of microemulsion, miniemulsion, oil‐in‐oil emulsion, and micellar polymerizations are provided. Current and potential developments of so‐called “hairy latexes”, inverse‐, multiple‐, and solid emulsions, as well as of nonaqueous polymeric dispersions are also discussed.
PS foam obtained by free radical polymerization of water‐in‐styrene, stabilized with a PS–PEO diblock copolymer. 相似文献