Polyreactions in miniemulsions

The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.

Miniemulsion Polymerization and the Structure of Polymer and Hybrid Nanoparticles

Emulsion polymerization mechanisms and kinetics

The formulation of micronutrients and nutraceuticals in the design of functional foods brings enormous technological challenges. The incorporation of micronutrients and/or nutraceuticals can compromise the product functionality. Issues often encountered are related to unwanted changes in the product physico-chemical stability, appearance, texture, flavour, taste and bioavailability due to inherited instability or interactions with other ingredients. This review intends to present the general strategies in using colloidal dispersions as delivery systems for micronutrients and nutraceuticals. Some illustrative examples will be given on how colloidal delivery systems can be utilised in the design of novel functional foods.

Colloidal delivery systems for micronutrients and nutraceuticals

▪ Abstract Miniemulsions are specially formulated heterophase systems in which stable nanodroplets of one phase are dispersed in a second, continuous phase. Because each of the nanodroplets can be regarded as a nanoscopic, individual batch reactor, a whole variety of reactions and processes resulting in both organic and inorganic nanoparticles can be performed. This chapter reviews the wide range of possibilities of reactions in miniemulsions for the formation of structured nanoparticles. Different kinds of polymerizations, such as radical, anionic, and enzymatic polymerization, as well as polyaddition and polycondensation can be carried out in the nanodroplets, which permits the formulation of a variety of polymers, copolymers, or hybrid particles that previously have not been synthesized in other heterophase processes. Additionally, this review shows that miniemulsions are also highly suited for the encapsulation of various organic and inorganic, solid or liquid materials and for the functionalization o...

Synthesis of colloidal particles in miniemulsions

Emulsion and miniemulsion copolymerizations were carried out with acrylic monomers (methyl methacrylate, butyl acrylate, and acrylic acid) in the presence of an alkyd resin. Poly(methyl methacrylate) was used as a hydrophobe or cosurfactant in the miniemulsion reactions. The results demonstrate that miniemulsion polymerization is the preferred process, probably because of mass transport limitations of the alkyd in the conventional emulsion polymerization reactions. The monomer emulsions prepared for the miniemulsion reactions were much more stable and the polymerizations were free of coagulum. Reaction rates, particle size characteristics, grafting efficiencies, and some film properties were measured. © 1996 John Wiley & Sons, Inc.

Emulsion and miniemulsion copolymerization of acrylic monomers in the presence of alkyd resin

Miniemulsion polymerization of styrene with the chain transfer agent n-dodecyl mercaptan (DDM) used as cosurfactant was studied. Droplet size and shelf life for unpolymerized miniemulsions were measured and compared with those of equivalent macroemulsions. The miniemulsion monomer droplets with dodecyl mercaptan as cosurfactant were very stable. Shelf lives were from 17 h to 3 months. The kinetics of miniemulsion polymerization were studied. Unlike other miniemulsion systems where the cosurfactant does not act as a chain transfer agent, the polymerization rate falls with cosurfactant level because the chain transfer agent enhances radical desorption from the particles. The polymerization rate in all the miniemulsions was lower than that of the corresponding macroemulsions. Polymerized particles were larger than in the corresponding macroemulsions, but molecular weights were lower. Results indicate that DDM can serve as an effective cosurfactant as well as a chain transfer agent. The fact that the molecular weights are lower in the miniemulsion reactions indicates predominant droplet nucleation. © 1997 John Wiley & Sons, Inc.

Miniemulsion polymerization of styrene with chain transfer agent as cosurfactant

Low molecular weight species, formed during the emulsion copolymerization of styrene and acrylic acid, were isolated and characterized. Samples of the reaction mixture were taken at different times during seeded and unseeded batch reactions. Reactions were stopped via injection of the samples into hydroquinone solutions and cooling with dry ice. Low molecular weight copolymers were separated and FTIR spectroscopy, mass spectroscopy, and 13C–NMR spectroscopy techniques were used to measure the oligomer composition, molecular weight, and copolymer sequence distribution, respectively.



The molecular size measurements should relate to the size of oligomeric radicals that grow in the water phase and enter polymer particles and the measurements should also relate to any water-soluble polymer that is formed by termination in the aqueous phase. The molecules, found for copolymers formed from 90/10 weight ratios of styrene and acrylic acid, were comprised of 6–9 monomer units with 2–3 being styrene. Those formed from 60/40 styrene/AA ratios contained 13–16 monomer units with 1–2 styrene. Differences were observed between seeded and unseeded systems, especially in the amount and nature of the water-soluble material formed early in the reaction. © 1993 John Wiley & Sons, Inc.

Characterization of water-soluble oligomer in acrylic acid-styrene emulsion copolymerization

The stability of vinyl acetate miniemulsions employing polyvinyl alcohol (PVOH) as the surfactant, and hexadecane and/or various polymers as the cosurfactant, were studied. Shelf lives (to phase separation) and monomer droplet sizes were measured. The results indicate that it is possible to prepare stable miniemulsions using a nonionic surfactant (PVOH) and hexadecane as the cosurfactant. Polymeric cosurfactants do not create stable miniemulsions but retard Ostwald ripening to an extent that allows predominant droplet nucleation. The polymerization behavior of these miniemulsion systems was investigated using on-line conductance measurements to differentiate droplet versus micellar/homogeneous nucleation. The effect of cosurfactant concentration on the reaction rate was compared for hexadecane and polymeric cosurfactants. © 1994 John Wiley & Sons, Inc.

Miniemulsion polymerization of vinyl acetate with nonionic surfactant

A polymer chain transfer agent was synthesized by the reaction between poly(vinylbenzyl chloride) latex particles and 2-aminoethanethiol in a basic environment. In subsequent emulsion polymerization reactions, low molecular weight species were formed when waterborn oligomeric radicals diffused to the surface of these seed particles. These low molecular weight oligomers were separated by membrane filtration and their composition and molecular weight weight were analyzed by FTIR and mass spectroscopy. The measured composition results were compared with those that were calculated from the copolymerization equation. The molecular weights were compared with earlier experimental results that were obtained by isolation of oligomers formed when a water-soluble inhibitor was added to a reacting emulsion.



Three seeded emulsion copolymerization systems, that is, styrene–acrylic acid, styrenemethacrylic acid, and styrene–methyl methacrylate, were investigated. The distribution of monomer in the water phase and in the copolymer particles was analyzed. The results show that the oligomer compositions for different copolymerization systems can be approximated reasonable well by the copolymerization equation, using the reactivity ratios obtained from bulk copolymerization. The length of the oligomer radicals formed depends on their composition and the properties of the polymer particles, such as surface charge, composition, size, and concentration. © 1994 John Wiley & Sons, Inc.

Shou‐Ting Wang

Papers

Emulsion and miniemulsion copolymerization of acrylic monomers in the presence of alkyd resin

Miniemulsion polymerization of styrene with chain transfer agent as cosurfactant

Characterization of water-soluble oligomer in acrylic acid-styrene emulsion copolymerization

Miniemulsion polymerization of vinyl acetate with nonionic surfactant

Studies of water‐soluble oligomers formed in emulsion copolymerization