Microgel precipitates

In the precipitation region, we observed that the mixed DTAB/PAMPS films were still more stable, impossible to rupture. The images of the films showed that microgel precipitates were trapped in the films and were prob-... 

Polymerization in dilute solution also allows a very straightforward isolation and purification of the microgels. After polymerization, the resulting microgels can be conveniently precipitated from the reaction solution by using suitable nonsolvents for the microgel molecules. The resulting powders can be filtered off, dried, and redispersed in suitable solvents when needed. 

The microgels could be conveniently isolated by precipitation as white powders, readily redispersable in many different organic solvents such as dialkylamides, nitriles, dichloromethane, acetone and THF. Further to this, the DMAA-based microgels exhibited a rather amphiphilic character and were also soluble in water and in alcohols such as methanol or ethanol in contrast, their counterparts based on MMA turned out to be more lipophilic and therefore insoluble in water and alcohols but soluble in organic solvents of low polarity such as toluene. 

Ester formation by dimethylsulfate or diazomethane is not satisfactory because the microgels become insoluble when the reaction proceeds to higher conversions. With diazomethane part of the unsaturated groups is involved in a side reaction of a 1,3-dipolar cycloaddition [132]. A more efficient method for ester formation of microgels is the reaction with 0-alkyl-N,N -bisisopropyl isoureas of the alcohols. The alkyl ureas are easily separated from solutions in methanol [294-296]. The esterified microgels were isolated by precipitation and freeze-drying. Depending on the alcohol used for ester formation, the yields of... 

Any colloidal material provides an intrinsically favorable accessibility to its surface when compared to bulk material. Therefore, the availability of receptor binding sites should be facilitated by using colloidal MIPs. Submicron scale MIPs were prepared by precipitation polymerization, emulsion polymerization, and miniemulsion polymerization. Precipitation polymerization uses the insolubility of the formed polymer microgel in a certain solvent, whereas emulsion and miniemulsion polymerization employ two solvent phases for the preparation of the colloidal polymer. The latter methods offer the opportunity for tailoring the surface of the colloids exclusively, thereby enhancing the accessibility of the binding sites. Each of the three approaches has their own characteristics and will be described in the following sections. 

Cationically-charged microgel particles Precipitation polymerization of NIPAM or NIPMAM with a crosslinker (MBA) and AEMH 200-1000 nm Cationic surface charge. Swelling capacity dependent on MBA amount [12]... 

Microgels can be prepared by heterophase polymerization (free radical or controlled radical) of monomers in the presence of a crosslinking agent in aqueous phase. Heterophase polymerization techniques suitable for microgel synthesis are precipitation polymerization and inverse mini- and microemulsion. 

During precipitation polymerization, all ingredients are dissolved in a solvent (water) to form a homogeneous mixture in which initiation of polymerization takes place. The formed polymers are transformed into a collapsed state because the reaction temperature is far above VPTT (for example in the case of PNIPAAm) and become crosslinked by crosslinker molecules to form a colloidal polymer network or microgel. This technique has been widely used for the synthesis of thermosensitive PNIPAAm [30-35] and poly(/V-vinyl caprolactam) (PVCL) [36] microgels. 

The precipitation polymerization is a versatile technique and offers several advantages for the preparation of aqueous microgels ... 

Different ionic monomers were copolymerized with NIPAAm or VCL to obtain pH- and temperature-sensitive microgels. Snowden et al. [65] reported preparation of aqueous microgels by copolymerization of NIPAAm and acrylic acid (AAc) in a precipitation polymerization process. The AAc content was 5wt%. Obtained microgels displayed pH and electrolyte sensitivity, as well as temperature sensitivity. 

The copolymerization of different functional monomers during precipitation polymerization can be used for design of amphoteric aqueous microgels [76-82], Amphoteric microgels were prepared by copolymerization of NIPAAm with acrylic acid and vinylimidazole (Vim) [76-80], Alternatively, Tan and coworkers prepared amphoteric colloids by copolymerization of acrylic acid, 2-(diethylamino)ethyl... 

Precipitation polymerization allows preparation of microgel particles with a coreshell structure. This can be achieved by using monomers of different reactivity or hydrophilicity in a batch polymerization process. Alternatively, core-shell microgels can be prepared by seed polymerization techniques or by stepwise addition of co-monomers to the reaction mixture. 

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