Precipitation Polymerization Methods

Their size was ideal for their convenient removal at the end of any reaction by means of filtration. Because of their favorable initiation properties, only molybdenum-based initiators were used, which were removed quantitatively in 

In analogy with carboxylate-functionalized beads, di-pyridylamide-based resins were synthesized. In contrast to di-pyridylamine, the corresponding amide revealed a high selectivity for both mercury(II) and palladium(II) [10]. This allowed the selective enrichment of these two transition-metal ions from aqueous solutions over a concentration range covering several orders of magnitude [11]. 

In addition, a palladium(II)-loaded resin was successfully used as heterogeneous Heck, Sonogashira-Hagihara, and amination catalysts [12]. Based on these encouraging results, a variety of different methylpyridyl- and bis(pyrimidyl)-derivatized supports were prepared from NBE derivative monomers containing ligands 2-6 (Table 11.1) [12-15, 21-23]. 

Barrett created the term ROMPgel for linear polymers, which swell but do not dissolve in certain solvents because of solubility restrictions governed by the nature of the functional monomer used. Such ROMPgels were prepared with a variety of different functional groups including phosphines [3], allyl-boronates [25], a polymeric Tosmic reagent [26], naphthalenes, and biphenyls [27], alkylphosphonates [28], as well as anhydrides [29], some in a precipitation polymerization setup similar to the one described by our group. 

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The aim of our work was to develop a fast, simple and selective CL imaging assay coupled with MIP for the chiral recognition of fluorescence labeled phenylalanine. The precipitation polymerization method was used for preparing MIP microspheres with uniform shape. Figure 2 shows the dansyl-L-phenylalanine molecular imprinting process. The average diameter of microspheres was about 0.7 pm. 

Figure 15 SEM micrograph of polyferrocenylsilane microspheres formed from precipitation polymerization methods with average particle diameters of 2.1 iim (Reproduced with permission of The American Chemical Society from Kulbaba, K. et al., J. Am. Chem. Soc., 2002, 124, 12522.)...

The low temperature precipitating polymerization method comprises the polymerization reaction in an organic solvent which is sparingly soluble in water, such as methyl ethyl ketone, and in an aqueous solvent by using triethylamine as an acid acceptor. This reaction is a kind of interfacial polymerization method. ... 

Once the polymer reaches a certain critical mass, this solvent is no longer able to hold the polymeric chain in solution, thus precipitating the particles off the solution. The polymerization temperature in which the solvent is able to hold the polymerization process up to a certain critical mass is known as theta [0) temperature. The polymer precipitates off the solution after this point. Solvents with this particularity for a given polymer are known as 6 solvents. Therefore, the selection of a proper 6 solvent is essential to obtain discrete particles in the precipitation polymerization method. 

The fabrication of thermoresponsive PG nanogels was recently developed by Calderdn et al. [35] in an attempt to develop stimuli-responsive materials based on dendritic PG. In this work, the precipitation polymerization method... 

In dispersion polymerization, the monomer and initiator are dissolved in the continuous phase, which acts as a nonsolvent for the developing polymer. The continuous phase can be organic, aqueous, or a mixture of miscible phases. Two methods of initiation have been employed, including gamma radiation [75] and chemical initiation by potassium perox-odisulphate [76]. As the polymer is formed, it precipitates as nanoparticles. These particles are not polymeric precipitates as in precipitation polymerization. Rather, they are swollen by a mixture of the monomer and the continuous phase [39],... 

Methods for making an MIP with appropriate selectivity are the subject of other chapters. Here only the format of the MIP is mentioned. Crushed and sieved bulk MIPs have been widely used for MISPE but uniformly sized and spherical formats (obtained e.g., by precipitation polymerization) are more convenient. The cost of making the MIP is not negligible if the development work is included. However, this is still less than the cost of making a new affinity phase and the MIPs are stable, easily reproduced, and may even be reused, if so wished. 

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. 

Mosbach and co-workers developed a method to prepare molecularly imprinted polymers by precipitation polymerization [24]. They started from a dilute, homogenous solution of the monomer methacrylic acid (MAA) and the crosslinker trimethylolpropane trimethacrylate (TRIM) or ethylene glycol dimethacrylate (EGDMA). The polymer formed in the presence of the template molecule 17/1-estradiol, theophylline, or caffeine contained a high proportion of discrete spheres of diameter less than a micron. Because the effect of coalescence becomes predominant with higher solid content of the reaction mixture, this approach is limited to solid contents of typically <2 wt%. 

Micron-size particles can also be prepared by polymerization of monomer dispersion in organic solvents (e.g. alcohol) in which the emerging polymer is not soluble. At the beginning of the process, the reaction mixture is homogenous but during the reaction, stabilized polymer particles precipitate. This method offers uniform particles with a diameter of 2-15 pm (40). 

Precipitation polymerization can be used for integration of inorganic NPs into microgel structures. An interesting approach for the preparation of the hybrid microgels is encapsulation of the NPs during precipitation polymerization. To demonstrate the efficiency of this method, LaF3 Eu NPs modified with a mixed... 

Controlled free-radical polymerization (CFRP) has been used successfully to produce block, graft, and other controlled architecture copolymers within the last decade for a variety of free radically polymerizable monomers. The main techniques include reversible addition fragmentation and transfer (RAFT) polymerization, stable free-radical polymerization (SFRP) mediated by nitroxide/alkoxyamine based radicals, atom transfer radical polymerization (ATRP), diphenyl ethylene (DPE) mediated polymerization, and novel precipitation/emulsion polymerization based methods like free-radical retrograde precipitation polymerization (FRRPP). ... 

For chromatographic applications, monodisperse spherical MIP particles are preferable to the irregularly shaped MIP particles formed by grinding and sieving the polymer monoliths. Consequently, some researchers have developed methods that produce spherical MIP particles through precipitation polymerization and emulsion polymerization. Monodisperse MIP microspheres were prepared by Mosbach et al. under similar conditions to the MIP monolith preparation but under significantly more dilute precipitation polymerization conditions. The MIP microspheres grew to 1-3 pm diameter with a narrow size distribution. 

Spherical beads possess better hydrodynamic and diffusion properties than irregularly shaped particles. It is, hence, desirable to apply MIPs in a spherical bead format, especially for flow-through applications. Methods to synthesize spherical polymer beads are often classified according to the initial state of the polymerization mixture (i) homogeneous (i.e. precipitation polymerization and dispersion polymerization) or (ii) heterogeneous (i.e. emulsion polymerization and suspension polymerization). In addition, several other techniques have been applied for the preparation of spherical MIP beads. The techniques of two-step swelling polymerization, core-shell polymerization, and synthesis of composite beads will be detailed here. 

Due to the beneficial health effects of trans-resveratrol in grape wine, many methods have been developed for its detection and quantification.1 In our laboratory, a MIP-based CL imaging sensor for determination of tram-resveratro 1 in grape wine has been developed. The MIP of trans-resveratro 1 was prepared by a precipitation polymerization using trans-resveratrol as the target molecule,... 

Microspheres based on metal-containing polymers should exhibit interesting redox, semiconductive, magnetic, and photonic properties intrinsic to the polymeric materials, and may prove useful for a variety of applications. The most common methods for microsphere preparation involve the use of steric stabilizers, which may adversely affect the properties of the resultant materials. This problem can be avoided by the use of a precipitation polymerization methodology, which allows for the autostabilization of the polymer microspheres without addition of stabilizers. This... 

A slight modification of the solution-polymerization method is of greater industrial importance. According to this procedure the monomer is mixed with a liquid that, while being a solvent for the monomer, precipitates the polymer from the solution. The polymer can be removed from the reaction mixture, and with the addition of new monomer, the process can be made continuous. 

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