## 3 Polymerization Methods for IIP Synthesis  
Several polymerization methods have been developed for the synthesis of ion imprinted polymers. Table 3 shows these methods, noting the general features of each one, as well as SEM images to observe the possible morphology of the polymeric particles after synthesis. * Bulk polymerization is the strategy traditionally employed for the synthesis of IIP. * The polymerization reaction is carried out in a homogeneous system, in which the reactants (metal ion, functional monomer, cross-linking reagent, and initiator) are dissolved in an appropriate solvent inside a sealed vial in the absence of oxygen. * Polymerization is induced with increased temperature and/or UV radiation. * The polymer obtained has a rigid and heterogeneous consistency, and it is necessary to employ after synthesis, grinding, and sieving procedures before use, to standardize the size of the particles. * Convenient for solid phase extraction of metal ions. * The imprinting effect, adsorption capacity, and selectivity of these polymers are lower compared to those obtained by other strategies, due to the incomplete removal of the template during washing after synthesis and the difficult access of the metal ion to the selective cavity. * During polymer grinding, the binding sites can be destroyed. Figure 8: Number of published papers on IIP from 1991 to 2022. Web of Science: ion-imprinted polymer and ion imprinted polymer (Accessed in August 2022). \begin{table}
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**Polymerization Methods** & **General Features** & **Examples of Polymeric Particle Morphology** \\ \hline \hline \end{tabular}
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Table 3: Polymerization methods of IIP and SEM images to observe the possible morphology of the polymeric particles after synthesis. The synthesis reagents are dissolved in non-polar organic solvent and then added in an immiscible phase (usually polar) containing stabilizing agents (surfactant) to form a dispersive phase (with the non-polar phase inside the micelle), preventing coagulation of the emulsion drops. The polymerization reaction takes place inside the emulsion droplets, after heating the medium under agitation, remaining in suspension with the dispersive phase, which causes the polymer to be produced in the shape of spheres. Water is usually used as the immiscible phase and polyvinyl alcohol and inorganic salts as surfactants. The stabilizer affects the size and shape of particles, as well as their crystallinity and transparency [72] It is noteworthy that water can solvate the metal ion interfering with the complexation, and it is necessary to use another dispersive phase, using a doughy appearance surfactant based on a perfluorocarbon polymer [75,76]. Preipitation polymerization is similar to bulk polymerization, but the solvent volume is different. It is 5-fold to prevent the formation of a compact polymer. The mixture of reagents and solvent is degassed and stored in a water bath at a temperature of 60 \({}^{\circ}\)C for 24 h or UV radiation. Preipitation occurs when the microsphere acquires greater density than the solution during the reaction, becoming insoluble. After synthesis, the microspheres are separated by centrifugation and washed with a solvent mixture to remove excess synthesis reagent. There is no formation of emulsions. \begin{table}
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** Polymerization Methods** & **General Features** & **Examples of Polymeric Particle Morphology** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Cont. * Initially, the surface of the solid support is activated or chemically modified to anchor molecules that have a vinyl group in the structure so that polymerization occurs. * The support material is usually inorganic (silica gel or magnetite nanoparticles), which are chemically and mechanically stable materials regarding organic solids, such as cellulose. * All reagents are dissolved in the solvent and mixed with the supporting solid.