Copolymerization Core-shell” particles

Alternative approaches involving molecules that combine the properties of a monomer with those of a surfactant (so-called polymerizable surfactants) have also been reported. For example, quaternary alkyl salts of dimethyl aminoethyl methacrylate (CnBr) surfactants were used to promote polymer encapsulation of silica gels in aqueous suspension [43, 44]. The polymerizable surfactant formed a bilayer on the silica surface, the configuration of which enabled the formation of core-shell particles. The CnBr amphiphilic molecule was either homopolymer-ized or copolymerized with styrene adsolubilized in the reactive surfactant bilayer. This concept of admicellar polymerization is detailed in Sect. 3.1. In the recent... 

The presented three step method of inorganic particle preparation, consequent functionalization and finally embedding into a miniemulsion copolymerization system offers an easy way to prepare core shell particles with a wide range of functionalities at the surface. Those products inherit a high potential as reactive filler materials in advanced polymers composites. 

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). 

The copolymer composition in miniemulsion copolymerization of vinyl acetate and butyl acrylate during the initial 70% conversion was found to be less rich in vinyl acetate monomer units [34]. Miniemulsion polymerization also allowed the synthesis of particles in which butyl acrylate and a PMMA macromonomer [83, 84] or styrene and a PMMA macromonomer [85] were copolymerized. The macromonomer acts as compatibilizing agent for the preparation of core/shell PBA/PMMA particles. The degree of phase separation between the two polymers in the composite particles is affected by the amount of macromonomer used in the seed latex preparation. 

Temperature- and pH-sensitive core-shell microgels consisting of a PNIPAAm core crosslinked with BIS and a polyvinylamine (PVAm) shell were synthesized by graft copolymerization in the absence of surfactant and stabilizer [106] The core-shell morphology of the microgels was confirmed by TEM and zeta-potential measurements. Other examples of core-shell microgel systems are PNIPAAm-g-P(NIPAM-co-styrene) colloids [107] or PS(core)-g-PNIPAAm (shell) particles [108],... 

Core-shell polystyrene-polyimide high performance particles have been successfully prepared by the dispersion copolymerization of styrene with vinyl-benzyltrimethyl ammonium chloride (VBAC) in an ethanol-water medium using an aromatic poly(amic acid) as stabilizer, followed by imidization with acetic anhydride [63]. Micron-sized monodisperse polystyrene spheres impregnated with polyimide prepolymer have also been prepared by the conventional dispersion polymerization of styrene in a mixed solvent of isopropanol/2-methoxyethanol in the presence of L-ascorbic acid as an antioxidant [64]. 

Seeded emulsion polymerization can be used with batch, semi-continuous, or continuous polymerization to give the desired value of N, In batch or semi-continuous emulsion polymerization, seeding ensures batch-to-batch reproducibility of the final particle size in continuous emulsion polymerization, it ensures the reproducibility, not only of the final particle size, but also of the conversion of the exit stream. Seeded emulsion polymerization is equally adaptable to emulsion homopolymerization and copolymerization. Moreover, two-stage or multiple-stage polymerizations can be used to produce core-shell latex particles the variation of the process type---batch, semi-continuous, continuous----as well as the para-... 

This second set of nonionic surfmers was engaged in core-shell emulsion copolymerization of 1 1 tyrene-butyl acrylate, in comparison with a commercial nonionic surfactant NP30 [85]. High conversions were obtained in all cases, with limited amounts of floe at solid contents of 35%. To reach the targeted size of 240 nm, the amount of surfactant must be adjusted. Too much surfactant causes nucleation of new particles without decreasing the amount of floe, whereas in the reverse case limited flocculation is observed (slightly larger particles) and more floe is produced. 

The polymer particles with heterogeneous structure (e.g., core-shell, rusberry-like...) can be form by the classical batch emulsion copolymerization of unsaturated monomers with different reactivities and hydrophobicities. For example, the emulsion copolymerization of butyl acrylate and vinyl acetate gave polymer particles with a butyl acrylate-iich core and a vinyl acetate - rich shell [67]. The similar stmcture of polymer particles were reported in the emulsion copolymerization of acrylonitrile with hydrophobic unsaturated monomers such as bulyl aciylate [68]. 

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