Macromolecular core-shell particles

Figure 22 Sketch of the preparation of macromolecular core-shell particles via grafting of a monomer on a initiator-group containing a cross-linked core, (a) Mixture of monomer, cross-linker and azo-group containing monomer emulsified in water, (b) Reactive cross-linked core, (c) Core-shell particle [254,255]...

Landfester, K. and Musyanovych, A. (2007) Core-shell particles, in Macromolecular... 

Another procedure for the preparation of modified thermosets consists of introducing preformed particles in the initial formulation. This technique is also well documented for modified thermoplastics (Paul and Bucknall, 2000). In Chapter 7 different macromolecular architectures such block copolymers, crosslinked microparticles, hyperbranched polymers, and den-drimers, were presented (Fig. 7.11). All these compact molecules can be used as thermoset modifiers. Thermoplastic powders and core-shell polymers are the more accessible preformed molecules. Some examples are given below. 

The compatibilization strategies comprise (i) addition of a small quantity of cosolvent - a third component, miscible with both phases, (ii) addition of a copolymer whose one part is miscible with one phase and another with another phase, (iii) addition of a large amount of a core-shell copolymer - a compatibilizer-cum-impact modifier, (iv) reactive compounding that leads to modification of at least one macromolecular species that result in the development of local miscibility regions, and (v) addition of a small quantity of nanoparticles which influence blend structure similarly to particle-stabilized water/oil emulsions. 

L.S. Peixoto, F.M. SUva, M.A.L. Niemeyer, G. Espinosa, P.A. Melo, M. Nele, J.C. Pinto, Synthesis of poly(vinyl alcohol) and/or poly(vinyl acetate) particles with spherical morphology and core-shell structure and its use in vascular embolization, Macromolecular Symposia 243 (2006) 190-199. 

M.D. Besteti, A.G. Cunha, D.M.G. Freire, J.C. Pinto, Core/shell polymer particles by semibatch combined suspension/emulsion polymerizations for enzyme immobilization, Macromolecular Materials and Engineering 299 (2014) 135-143. 

In the synthesis of these macromolecular system, many parameters involved can affect the information associated with the binding sites, such as functional monomers/polymers, crosslinkers and solvents/porogens. Thus, both the feasibility of imprinting and the proper preparation conditions need exploration for the preparation of efficient imprinted materials (Liu Z. et al., 2010). It is important to state that MIP can be obtained in different formats, depending on the preparation method followed. To date, the most common polymerizations for preparing MIPs involve conventional solution, suspension, precipitation, multi-step swelling and emulsion core-shell. There are also other methods, such as aerosol or surface rearrangement of latex particles, but they are not used routinely (Puoci et al., 2011). 

Cholesterol and triacylglycerols are transported in body fluids in the form of lipoprotein particles. Each particle consists of a core of hydrophobic lipids surrounded by a shell of more polar lipids and apoproteins. The protein components of these macromolecular aggregates have two roles they solubilize hydrophobic lipids and contain cell-targeting signals. Lipoprotein particles are classified according to increasing density (Table 26.1) chylomicrons, chylomicron remnants, very low density lipoproteins (VLDL), intermediate-density lipoproteins (IDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Ten principal apoproteins have been isolated and characterized. They are synthesized and secreted by the liver and the intestine. 

Special proteins, called apoLipoproteins, are required for handling and traruv port of lipid droplets. These proteins are synthesized on the ER and enter the lumen of the ER, where they are assembled into large macromolecular structures. The relevant proteins include apolipoprotein A apo A) and apo lipoprotein B (apo B), Apo A and apo B combine with lipid droplets to form structures called chylomicrons, microscopic particles with large cores of lipid coated with a thin shell of protein. The chylomicrons are transferred to secretory vesicles, which migrate through the cytoplasm to the basal membrane of the cell. Here the vesicles fuse with the membrane, resulhng in the expulsion of chylomicrons from the cell. (If the vesicles fused with the apical membrane of the enterocyte, the effect would be a futile transfer of the dietary lipids back to the lumen of the small intestine.)... 

The model used in the above studies ignores the departure from the bulk density of the adsorbate brought about by the interaction of the two interfaces. Li and Caldwell s article addresses this issue by introducing a three-component model consisting of a core particle, a flexible macromolecular substance with affinity toward the particle, and a solvation shell (see Fig. lb). 

Figure 5 Experimental SAXS data from a composite latex with a polystyrene core and a poly(methyl methacrylate) shell. The number average diameter is 92.8 nm. The inset displays the electron density cross-section of the particle derived from contrast variation studies. Reproduced with permission of Huthig Wepf Verlag from Ballauff MB, Bolze J, Dingenouts N, HickI P. and Pbtschke D (1996) Small-angle X-ray scattering on latexes. Macromolecular Chemistry and Physics 197 3043-3066.

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