Polymers core shell grafts

Z. Cui, B. Yang, Monodisperse silica-polymer core-shell microspheres via surface grafting and emulsion polymerization. Macromol. Mater. Eng. 2003, 288, 380-385. 

Barahona, R, Turiel, E., Cormack, P A. G., Martin-Esteban, A., Chromatographic Performance of Molecularly Imprinted Polymers Core-Shell Microspheres by Precipitation Polymerization and Grafted MIP Films via Iniferter-Modified Silica Beads, 1. Polvm. Sci. A Polvm. Chem. 2010,48,1058-1066. 

Fig. 5-4. Schematic representation of composite polymeric particles. (A) Surface coating, (B) pellicular, (C) core shell graft, (D) pore matrix composite, (E) interpenetrating polymer networks.

Activation and functionalisation of polymeric particles can be carried out to produce liquid chromatography adsorbents with a range of functionalities. The type of chemistries employed will depend upon the chemical nature of the polymer and the required final product functionalities. Covalent attachment may be carried out, as is required for core shell grafts or coatings applied which may or may not be further derivatised. In all cases it is essential that the derivative is stable to the chromatographic conditions employed and any clean up procedures used. 

Generally, the number of the shell chains in a microsphere ranges from a few hundred to a few thousand. The range of the diameter of the core is from 10-100 nm. Such a core-shell structure is very similar to the (AB)n type star block copolymers, which have many arms and spherical polymer micelles of the block or graft copolymers formed in selective solvents that are good for the corona sequence and bad for the core sequence. In fact, many theoretical investigations of the chain con-... 

Thermoplastic elastomers (TPE), 9 565-566, 24 695-720 applications for, 24 709-717 based on block copolymers, 24 697t based on graft copolymers, ionomers, and structures with core-shell morphologies, 24 699 based on hard polymer/elastomer combinations, 24 699t based on silicone rubber blends, 24 700 commercial production of, 24 705-708 economic aspects of, 24 708-709 elastomer phase in, 24 703 glass-transition and crystal melting temperatures of, 24 702t hard phase in, 24 703-704 health and safety factors related to, 24 717-718... 

More recently, the scope of using hyperbranched polymers as soluble supports in catalysis has been extended by the synthesis of amphiphilic star polymers bearing a hyperbranched core and amphiphilic diblock graft arms. This approach is based on previous work, where the authors reported the synthesis of a hyperbranched macroinitiator and its successful application in a cationic grafting-from reaction of 2-methyl-2-oxazoline to obtain water-soluble, amphiphilic star polymers [73]. Based on this approach, Nuyken et al. prepared catalyticaUy active star polymers where the transition metal catalysts are located at the core-shell interface. The synthesis is outlined in Scheme 6.10. 

Different architectures, such as block copolymers, crosslinked microparticles, hyperbranched polymers and dendrimers, have emerged (Fig. 7.11). Crosslinked microparticles ( microgels ) can be described as polymer particles with sizes in the submicrometer range and with particular characteristics, such as permanent shape, surface area, and solubility. The use of dispersion/emulsion aqueous or nonaqueous copolymerizations of formulations containing adequate concentrations of multifunctional monomers is the most practical and controllable way of manufacturing micro-gel-based systems (Funke et al., 1998). The sizes of CMP prepared in this way vary between 50 and 300 nm. Functional groups are either distributed in the whole CMP or are grafted onto the surface (core-shell, CS particles). 

Important parameters that control the size of micelles are the degree of polymerization of the polymer blocks, NA and NB, and the Flory-Huggins interaction parameter %. The micellar structure is characterized by the core radius Rc, the overall radius Rm, and the distance b between adjacent blocks at the core/shell-interface as shown in Fig. 1. b is often called grafting distance for comparisons to polymer brush models, b2 is the area per chain which compares to the area per head group in case of surfactant micelles. In the case of spherical micelles, the core radius Rc and the area per chain b2 are directly related to the number of polymers per micelles, i.e., the aggregation number Z=4nR2clb2. 

Two kinds of photoresponsive azobenzene polyurethane functionalized multiwalled carbon nanotube (AzoPU-MWNT) composites were synthesized by in-situ polycondensation (50). Core-shell structures with MWNTs as hard core and polymer layer as soft shell were formed and the average thickness of the grafted polymers was about 7-10 nm. The AzoPU-MWNT composites showed reversible photoisomerism behavior. 

In all instances of the dispersion polymerization, amphiphilic graft copolymers produced in a selective solvent for the branches play a crucial role. Schematically, a microsphere obtained by copolymerization in this way with a small amount of macromonomer has a core-shell structure as given in Fig. 2, with the core occupied by the insoluble substrate polymer chains and the shell by the soluble, graft-copolymerized macromonomer chains. The backbone chains of the graft copolymers, which must be insoluble in the medium, serve as the anchors into the core. The following section presents general criteria for the size control of polymeric microspheres by dispersion copolymerization... 

The use of core-shell impact modifiers for sPS is also patented in EP 318793 [15] (see Table 19.1). These impact modifiers are usually prepared using the emulsion polymerization process, although other methods such as the microsuspension polymerization process are possible. The core usually consists of polymers prepared from an acrylate, especially butyl or 2-ethylhexyl acrylate or butadiene. These rubber particles are then grafted with vinyl monomers, where... 

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