# Microsphere Polymers in Molecular Imprinting: Current and Future Perspectives
## 3 Preparation of Molecularly Imprinted Microspheres
### Suspension Polymerisation
Different dispersing agents such as water and perfluoro-1,3-dimethylcyclohexane were explored by [PERSON] [140] and led to similar structures and sizes, but did not affect the shape significantly. MIM and NIM polymers have significant differences. Polymers with MIMs have an irregular, rough morphology with many small cavities caused by the template molecule structure. Polymers with NIMs have a more uniform, smooth shape. This shows that MIMs can be a potential sorbent for the separation and enrichment of analytes from a matrix [119]. [PERSON] [80] showed that the IF for erythromycin is 3.86. This indicates that the MIP has high specific adsorption for the template. In other experiments using different template molecules, melamine showed an IF of 4.1, meaning that melamine as a template molecule bound four times higher to MIMs than to NIMs [119]. To sum up the discussion of various polymerisation techniques in the preparation of MIMs, some advantages and disadvantages of each technique are provided in Table 2.  
To compare the effects of different polymerisation technique, we made some comparison of binding affinity and IF with the same template molecule. Microsphere polymers made for nicotine with precipitation polymerisation and RAFTPP were made from MAA as a functional monomer [56; 57]. Precipitation polymerisation resulted in an IF value of 10.5 for S-nicotine; meanwhile, RAFTPP has IF 3.33 in the synthesis of these two methods using different ratio compositions of template:monomer:crosslinker, namely 1:4:20 for precipitation polymerisation and 1:3:12 for RAFTPP. It could not be concluded whether the lower IF value of RAFTPP made this technique have lower polymer performances due to the different composition of the monomer and crosslinker. The crosslinker in the RAFTPP technique has a lower ratio towards the template and monomer compared to precipitation polymerisation. [PERSON] et al. [141] explained that less crosslinker will create long, free polymer chains within large pore diameters and low mass transfer resistance due to fewer crosslinking sites. Another result from [PERSON] et al. [142] shows that a large amount of functional monomer typically results in more non-specific interaction sites. Meanwhile, inadequate functional groups produce less complexation in the polymerisation process. In other results on imprinted polymers for 17\(\beta\)-estradiol, we found that all polymerisation techniques could give IF more than 1 [40; 41; 49; 50; 109]. The highest IF values were obtained from ATRPP techniques with high affinity binding and fast kinetics with 4-VP monomer. [PERSON] et al. [52] and [PERSON] et al. [88] made bisphenol A microsphere polymer using precipitation polymerisation. A polymer made from 4-VP monomer with 16.7% relative crosslinker to total volume [88] has a higher IF value than 28.6 vol% made by [PERSON] [52]. [PERSON] et al. [143] reported that the coagulation of the growing polymer microsphere was prevented by the crosslinker, but too large a crosslinker ratio will result in coagulation, because increasing the solvency of the continuous phase swelled the particles' surfaces and made them more prone to coagulation. Coagulation will lead to unfavourable mass transfer and lower binding. A microsphere-imprinted polymer for bisphenol A made by Pickering emulsion polymerisation has a larger IF value than PP [52; 87], but those two methods have lower IF values than ATRPP. These results cannot be used conclude that ATRPP was a better method than the others, since different ratio compositions of template:monomer:crosslinker were used. A summary of three different templates made with different technique of polymerisation can be seen in Table 3. Future investigations to conclude which technique is better still need to be done with the same ratio composition of template:monomer:crosslinker with the same volume and type of solvent.