# Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives
## 3 Preparation of Molecularly Imprinted Microspheres
### Controlled/Living' Radical Precipitation Polymerisation (CRPP)
#### 3.2.3 Reversible Addition-Fragmentation Chain Transfer Precipitation Polymerisation (RAFTPP)
The properties of the hydrophilic surface in the grafted and ungrafted MIM/NIM particles could be investigated by comparing their static water contact angle. This outcome showed a significant difference between the grafted and ungrafted MIM film, as the grafted MIM film showedgreater hydrophilicity compared to the ungrafted one. The grafted MIM/NIMs also showed a reduction in non-specific binding in pure aqueous solution, thus increasing water compatibility. This approach was highly useful, since it allows any kind of hydrophilic monomer to be grafted onto the MIM surface and requires no additional of functional or hydrophilic comonomers in the molecular imprinting system, thus making it less complicated and more efficient (requires no time for the optimisation of MIM formulation components). The stimuli-responsive MIMs (in this case, thermo-responsive) showed significantly decreased specific template binding of the grafted MIMs at a higher temperature (45 \({}^{\circ}\)C) compared to ambient temperature in a pure aqueous solution, likely because the polymer brushes collapsed at the higher temperature and blocked the binding sites. Not only brush layers are used for grafting, as [PERSON] et al. (2019) also demonstrated the use of a crosslinker (such as methylene bisacrylamide (MBA) to produce a hydrogel layer. This approach widens the scope of this versatile surface-grafting approach. Later on, a new strategy that allows for the more effective controlled synthesis of pure water-compatible MIMs with surface-grafted hydrophilic polymer brushes via facile one-pot RAFTPP was developed, using two types of CTA, a normal RAFT agent and hydrophilic macromolecular chain-transfer agents (Macro-CTAs, such as PEG Macro-CTAs and poly(N-isopropylacrylamide) [PNIPAAm]) [8]. Macro-CTAs play the role of a coCTA and steric stabiliser. Figure 4: The mechanism of the reversible addition-fragmentation chain transfer (RAFT) polymerisation (**a**), RAFTPP (**b**). M, monomer; (1), propagating radical; (2), thiocarbonylthio compound as RAFT agent; S, sulphur; R, free radical leaving-group that is capable of reinitiating polymerisation; Z, group that modifies the activity of the RAFT agent; (3), intermediate radical; (4), dormant species; (5), fragment radical. The results show a significant increase in both surface hydrophilicity and pure water-compatible template binding properties for grafted MIMs prepared with hydrophilic Macro-CTAs, making this method highly favourable for producing a water-compatible MIM. Another study using Macro-CTAs was conducted by incorporating a fluorescent monomer 2-hydroxyethyl anthracene-9-carboxylate methacrylate (AnHEMA) into the RAFTPP system [75], giving them analyte binding-induced fluorescence quenching properties. Therefore, the MIMs were able to act as optical chemosensors for direct drug quantification in a biological matrix, skipping any sample pretreatment, thus making it an effective and efficient method. Considering the great potential of stimuli-responsive MIMs, [PERSON] et al. [71] developed a new MIM that has both thermo- and photoresponsive properties in a pure aqueous environment via RAFTPP by surface-grafting an azo-containing MIM layer and thermo-responsive PNIPAAm brushes. The azo group's configuration can be controlled by light irradiation, thus generating an alteration in the structural arrangement of the binding sites that affects binding functionalities, resulting in a significant modification of the strength of host-guest interactions. This method resulted in orange-yellow MIP and NIP particles, demonstrating the presence of the azo-containing polymer layer on the core of the MIM. The photoresponsive properties of the grafted MIMs were shown by their photoregulated ability to take up and release the template in pure aqueous solutions. UV light irradiation led to the release of the template from the MIMs into the solution, shown by a decrease in equilibrium template binding capacity.