Miniemulsion polymerisation

More recently, Priego-Capote et al. reported on the production of MIP nanoparticles with monoclonal behaviour by miniemulsion polymerisation [63]. In the synthetic method that they employed, they devised to use a polymerisable surfactant that was also able to act as a functional monomer by interacting with the template (Fig. 4). The crosslinker content was optimised at 81% mol/mol (higher or lower contents leading to unstable emulsions). In this way, the authors were able not only to produce rather small particles (80-120 nm in the dry state) but also to locate the imprinted sites on the outer particle surface. The resulting MIP nanobeads were very effective as pseudostationary phases in the analysis of (/ ,S)-propranolol by CEC. 

Fig. 4 Molecular imprinting at the nanoparticle surface by miniemulsion polymerisation. Reproduced with permission from [63]...

Only a few attempts were reported concerning the arrangement of MIP particles between two porous membranes, or their deposition on a single membrane. For example, Lehmann et al. used MIP nanoparticles with diameters between 50 nm and 300 nm imprinted with boc-L-phenylalanin-anilide obtained by miniemulsion polymerisation the selective rebinding properties as well as the hydrodynamic properties of the nanoparticles stacked between two polyamide membranes were studied [254]. 

Vaihinger D, Landfester K, Krauter I, Brunner H, Tovar GEM (2002) Molecularly imprinted polymer nanospheres as synthetic affinity receptors obtained by miniemulsion polymerisation. Macromol Chem Phys 203(13) 1965-1973... 

The primary distinction between miniemulsion and conventional emulsion polymerisation is the nucleation mechanism. In miniemulsion polymerisation (104,132, 193, 361) radicals from the water phase enter the dispersed monomer droplets directly to initiate polymerisation (i.e., the droplets act as individual reactors). This nucleation mechanism is referred to as droplet nucleation. Because of the small size and large surface area of the miniemulsion droplets, they are competitive for radicals relative to the homogeneous and micellar nucleation mechanisms. The monomer droplets polymerise to become polymer particles (275). Miniemulsion latex particles are typically prepared in the size range of 50 to 500 nm in diameter. 

Hybrid aqueous dispersions were prepared containing both acrylic resins and polyurethane to provide enhanced properties for coating applications. Nanosized (approximately 50 mn) hybrid latexes were prepared at 30 C by the redox-initiated miniemulsion polymerisation of n-butyl methacrylate monomer in the presence of a urethane prepolymer. A stabiliser, of low molecular weight and low water solubility, was required to obtain stable particles of the required size. 7 refs. 

A monomer preemulsion, used for miniemulsion polymerisation, was prepared by stirring a mixture of epoxy resin, acrylic monomers, surfactants, costabiliser and water. Miniemulsion polymerisation produced the composite latex. Methacrylic acid and/or dimethylaminoethyl methacrylate were added to introduce the functional groups into the composite latices. The functional groups were introduced either by batch polymerisation or two-stage polymerisation, the latex produced by the two-stage polymerisation method had good polymerisation stability, storage stability and solvent resistance. 11 refs. 

Journal of Rubber Research 4, No.l, 1st Quarter, 2001, p.28-37 MINIEMULSION POLYMERISATION OF A BIFUNCTIONAL MACROMONOMER... 

Details are given of the miniemulsion polymerisation of a hydrophobic bifunctional ethylene-butylene copolymer macromonomer. Polymerisation kinetics were examined using potassium persulphate and AIBN. Solubihties of the resultant latex film in toluene, chloroform and THE were investigated. 16 refs. 

The application of the miniemulsion polymerisation technique to the encapsulation of titanium dioxide inside PS latex particles was investigated. The dispersions were prepared by sonication of the titanium dioxide in the presence of polybutene-succinimide pentamine stabiliser. Latexes were characterised in terms of the encapsulation efficiencies and particle size. 36 refs. 

Macromolecular Symposia 151, Feb.2000, p.549-55 MINIEMULSION POLYMERISATION APPLICATIONS AND NEW MATERIALS... 

Hybrid miniemulsion polymerisation was carried out with methyl methacrylate, butyl acrylate, and acrylic acid in the presence of oil-modified PU resin. Latexes with... 

EVIDENCE FOR THE PRESERVATION OF THE PARTICLE IDENTITY IN MINIEMULSION POLYMERISATION... 

The efficiency of the stripping process is also influenced by the particle size distribution, in particular the existence of particles with a diameter of 2 pm and above, as is the case with latices produced by the microsuspension and miniemulsion polymerisation processes. For smaller latex particles, the rate determining processes are the diffusion of VCM from the surface of the PVC particle into the aqueous phase and from the aqueous into the gas phase. At larger sizes, there is a switch to the rate determining step being diffusion of the VCM through the solid PVC particle and then into the aqueous phase. 

Most of the ultrasonic polymerisation studies involve miniemulsion polymerisation process where both shear and radicals generated by acoustic cavitation at 20 kHz are important. However, Teo et al. [65] have also used high frequency (213 kHz) to successfully carry out microemulsion polymerisation. By manipulating the concentration of surfactant used to stabilise the emulsion droplets, shear forces needed to generate emulsion droplets could be avoided. 

Ouzineb K, Hua H, Jovanovic R, Dube MA, McKerma TE. Monomer compartinentalisation in miniemulsion polymerisation studied by infrared spectroscopy. C R Chim 2003 6 1343-1349. 

The book is focusing on emulsion polymerisation in combination with both conventional and controlled radical polymerisation. Except for miniemulsion polymerisation, more exotic techniques, such as inverse emulsion polymerisation, microemulsion polymerisation and dispersion polymerisation are not covered. Chapter 1 gives a historic overview of the understanding of emulsion polymerisation, while also focusing on the solution of the... 

Core-and-shell composite particles based on inorganic cores with a polymer shell have also been investigated by several researchers, but do not seem to have reached industrial products. The reason for this is probably the high cost and possibly limited benefits of this type of latexes compared to existing products. A similar type of product is composite particles based on pre-emulsified polymers such as epoxies or polyesters (alkyds) with a subsequent addition of new monomers and polymerisation. This technique is partly connected to the process of miniemulsion polymerisation described in Section 1.2.2. A type of core-and-shell particles or at least multiphase particles may be obtained in this type of process. However, industrial applications of this type of products are not found on a large scale yet. Applications of polymer particles, mainly made by emulsion polymerisation, in the biomedical field was concentrated initially in the areas of blood flow determination and in vitro immunoassays. Microspheres have been employed for the determination of myocardial, cerebral and other blood flow and perfusion rates. Polymer particles and lattices, in particular, have been extensively used in immunoassays, starting in 1956, with the development... 

Two main nitroxide families have been examined TEMPO (N1 in Figure 5.6) and derivatives (N2-N7) and SGI (NIO). With TEMPO, most of the results were related to styrene homopolymerisation and only a few articles reported the homopolymerisation of n-butyl acrylate (Georges et al, 2004) in addition to its copolymerisation with styrene. With SGI, the homo-, random and block copolymerisations were investigated for both styrene and -butyl acrylate monomers. Only in the case of styrene has the emulsion process been examined, and due to the difficulties encountered most authors turned their attention towards miniemulsion polymerisation. 

From these few reports, it can be concluded that nitroxide-mediated LRP is still a difficult process to achieve in db initio emulsion polymerisation. This is the direct consequence of the complex nucleation step and of an extensive droplet nucleation (Cunningham, 2003). Thus, the various groups decided to focus on miniemulsion polymerisation, in which such difficulties are naturally overcome. 

In a miniemulsion process, the monomer droplets behave as independent microreactors, which allow the use of the same reagents as in bulk. In that way, benzoylperoxide (BPO) was applied as an initiator in the miniemulsion polymerisation of styrene at 125°C, in conjunction with free TEMPO (Prodpan et aL, 2000) according to the recipe initially reported by Georges group in its pioneering work (Georges et aL, 1993). In another experiment. 

Similar systems of styrene miniemulsion polymerisation received careftil attention from Cunningham et al. (2002b) in particular, their purpose was to assess the effect of the water solubility of the initiator and the nitroxide on the quality of control. In the case of BPO as an initiator, two nitroxides were tested, namely TEMPO and hydroxy-TEMPO, the latter being much more hydrophilic than the former (Ma etai, 2001). The kinetics were actually not affected by the type of nitroxide selected, whereas TEMPO offered better control than hydroxy-TEMPO as far as the evolution of Mn with monomer conversion was regarded, especially in the early stage of the polymerisation reaction. These results confirm that the choice of a proper nitroxide with optimal hydrophilicity is actually crucial in miniemulsion, as it was also the case in emulsion. 

When the acyclic SG1 nitroxide was selected instead of TEMPO, the miniemulsion polymerisation of styrene could be performed at 90° C in the presence of AIBN as a monomer-soluble radical initiator (Lansalot et al, 2000). However, even after 24h the monomer conversion was incomplete owing to the persistent radical effect leading to the release of a high free nitroxide concentration. With the slow thermal autoinitiation of styrene at 90°C and the good stability of SGI in the studied medium, no consumption of the nitroxide excess could be achieved under such experimental conditions. Consequently, although the polymers exhibited good molar mass characteristics, the polymerisation was too slow to be really viable. 

When BPO was replaced by potassium persulphate, a water-soluble radical initiator, and the polymerisation was carried out at 135°C with a [TEMPO]o/[K2S208]o = 2.9 initial molar ratio, the miniemulsion polymerisation of styrene was particularly fast as conversion reached 87% within 6h (McLeod et al, 2000). This feature was actually assigned to the partition of TEMPO between the organic and the aqueous phase that would lead to a... 

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