## 2 Synthesis and Characterization of MIP
### Polymerization Technique
#### 2.2.4 Suspension Polymerization  
Suspension polymerization is an efficient technique (one-step polymerization) and one of the most systematic approaches for creating MIP beads, allowing for the formation of spherical particles with a large size (in the range from micrometers to millimeters). This technique can produce high-quality MIP beads in the size range of 5 \(\upmu\)m to 50 \(\upmu\)m. However, the utilization of water is unsuitable with the non-covalent imprinting methods. In addition, the use of liquid fluorocarbons has its drawbacks, including being a generally expensive process [55]. The general scheme for the suspension polymerization technique is shown in Figure 4.  
Suspension polymerization refers to the polymerization of monomers suspended in small droplets of water. It has two immiscible phases: continuous and dispersed. Functional monomers, initiators, porogens, and template molecules make up the dispersed phase. Polyvinyl alcohols are frequently used as a suspending agent in the continuous phase to improve their stability. Because a small droplet is comparable to a small unit from bulk polymerization, the shape and particle size of the polymer microspheres can be easily controlled. The porosity of the surface of the particles can be effectively adjusted by varying the amount of porogen. A suspending agent must be introduced to the solution to establish a protective film on the surface of the particles to prevent the particles from adhering to each other [56]. Polydatin was chosen as a template polyphenol by [PERSON] et al. [61] because of its large size and amphiphilic nature. The product obtained by a suspension polymerization technique, which included 4-VP as a functional monomer, EGDMA as a crosslinker, water/methanol as a solvent, n-heptane as an oil, and Span 80 as a surfactant, exceeded all other MIPs in terms of polyphenol uptake. This MIP was anticipated to have a maximum retention capability of q\({}_{\text{max}}\sim\)300 \(\upmu\)mol/g, which was substantially higher than the sorption capabilities described in the literature for comparable systems. The likely surface imprinting process caused by polydatin's amphiphilic characteristics was the factor for such a significant result. These interfacial processes are likely to be responsible for the superior performance found with this suspension product compared to precipitation particles. The SEM images of the polymer synthesized using the suspension polymerization technique is illustrated in Figure 3D. Contrarily, traditional techniques such as bulk, precipitation, in situ, and suspension technique uses large amounts of organic solvents. Water could potentially be a suitable alternative, owing to it generally being able to develop strong interactions with the template and/or monomers. However, water can destabilize the complex and interfere with the synthesis of the specific sites. Many of the limitations of the traditional MIP production processes can be solved by using green alternative solvents. Supercritical carbon dioxide (s\(\mathrm{CO}_{2}\)) is a green solvent that can potentially be used in polymerization techniques instead of typical organic solvents. The MIP will possess features including controlled morphology and homogeneous binding sites. Polymer synthesis in sc\(\mathrm{CO}_{2}\) has a number of advantages over conventional organic solvents, including the fact that it is aprotic and has high mass transfer and diffusivity, which is difficult to achieve with organic solvents. The ability to obtain polymers simply through depressurization, low toxicity, and low preparation costs, make sc\(\mathrm{CO}_{2}\) an appealing solvent to replace commonly used organic solvents. Presently, most commercially available monomers, including those often used in MIP synthesis, are soluble in sc\(\mathrm{CO}_{2}\).