Oil-in-Oil Emulsions: A Unique Tool for the Formation of Polymer Nanoparticles

Abstract

Polymer latex particles are nanofunctional materials with widespread applications including electronics, pharmaceuticals, photonics, cosmetics, and coatings. These materials are typically prepared using waterborne heterogeneous systems such as emulsion, miniemulsion, and suspension polymerization. However, all of these processes are limited to water-stable catalysts and monomers mainly polymerizable via radical polymerization. In this Account, we describe a method to overcome this limitation: nonaqueous emulsions can serve as a versatile tool for the synthesis of new types of polymer nanoparticles. To form these emulsions, we first needed to find two nonmiscible nonpolar/polar aprotic organic solvents. We used solvent mixtures of either DMF or acetonitrile in alkanes and carefully designed amphiphilic block and statistical copolymers, such as polyisoprene- b-poly(methyl methacrylate) (PI- b-PMMA), as additives to stabilize these emulsions. Unlike aqueous emulsions, these new emulsion systems allowed the use of water-sensitive monomers and catalysts. Although polyaddition and polycondensation reactions usually lead to a large number of side products and only to oligomers in the aqueous phase, these new conditions resulted in high-molecular-weight, defect-free polymers. Furthermore, conducting nanoparticles were produced by the iron(III)-induced synthesis of poly(ethylenedioxythiophene) (PEDOT) in an emulsion of acetonitrile in cyclohexane. Because metallocenes are sensitive to nitrile and carbonyl groups, the acetonitrile and DMF emulsions were not suitable for carrying out metallocene-catalyzed olefin polymerization. Instead, we developed a second system, which consists of alkanes dispersed in perfluoroalkanes. In this case, we designed a new amphipolar polymeric emulsifier with fluorous and aliphatic side chains to stabilize the emulsions. Such heterogeneous mixtures facilitated the catalytic polymerization of ethylene or propylene to give spherical nanoparticles of high molecular weight polyolefins. These nonaqueous systems also allow for the combination of different polymerization techniques to obtain complex architectures such as core-shell structures. Previously, such structures primarily used vinylic monomers, which greatly limited the number of polymer combinations. We have demonstrated how nonaqueous emulsions allow the use of a broad variety of hydrolyzable monomers and sensitive catalysts to yield polyester, polyurethane, polyamide, conducting polymers, and polyolefin latex particles in one step under ambient reaction conditions. This nonpolar emulsion strategy dramatically increases the chemical palette of polymers that can form nanoparticles via emulsion polymerization.

Pickering emulsions stabilized by self-assembled colloidal particles of copolymers of P(St-alt-MAn)-co-P(VM-alt-MAn)

“…Using colloid particles to prepare and stabilize emulsions, socalled ''Pickering" emulsions, has drawn increasing interest in recent years [1][2][3][4]. In contrast to conventional emulsions, which are usually thermodynamically unstable and stabilized by surfactants or amphiphilic linear copolymers, Pickering emulsions are often super-stable due to the nearly irreversible adsorption of the colloid particles at the oil/water interface because of the their high energy of attachment, which makes the final emulsions extremely stable with shelf life stabilities of months or even years [3,4].…”

“…In contrast to conventional emulsions, which are usually thermodynamically unstable and stabilized by surfactants or amphiphilic linear copolymers, Pickering emulsions are often super-stable due to the nearly irreversible adsorption of the colloid particles at the oil/water interface because of the their high energy of attachment, which makes the final emulsions extremely stable with shelf life stabilities of months or even years [3,4]. In Pickering emulsions, the colloid particles are wetted partially by oil and partially by water so they become surface-active, and then they are preferentially located or adsorbed at the oil/water interface.…”

Nanoparticles by ROMP in Nonaqueous Emulsions

“…[7] As no polymerizations were performed in these systems, the idea was recently taken up by our group and developed to perform polyadditions, [8] polycondensations, [9] or oxidative polymerization [10] for the preparation of polymer nanoparticles or even core/shell particles by a combination of different polymerization methods. [11,12] For even more sensitive catalysts such as metallocenes we developed a second emulsion system which is based on a perfluorinated solvent and a hydrocarbon. [13] However, catalytic polymerizations have not yet been performed in more polar nonaqueous systems such as N,N-dimethylformamide (DMF)/n-hexane.…”

Polímeros usados como sistemas de transporte de princípios ativos

“…Em alternativa, os copolímeros diblocos podem ser dissolvidos num solvente orgânico imiscível na água, como o clorofórmio e, em seguida, emulsificados com uma fase aquosa. Por evaporação do solvente volátil são formadas as nanopartículas [108] . O bloco hidrofílico normalmente utilizado é PEO, enquanto que os blocos hidrofóbicos incluem os poli(L-aminoácidos), o poli(L- …”