94
exposed functional groups of the preformed SAM. This strategy is very simple, but
steric repulsions can occur between the polymer chains, which can prevent the formation of dense polymers. If this happens, polymer chains will not be oriented perpendicularly to the solid surface. It is also particularly difficult to immobilize polymers
having high Mws, since the reaction between the final group of the polymer chain and
the end group on the SAM layer can be hindered (Murugan et al. 2015).
Zhou et al. (2016) reported a new ‘grafting to’ approach called ‘self-assemblyassisted-grafting to’. The key is that, here, the polymers are preassembled into twodimensional polymer single crystals with functional groups on the surface. The
chemical coupling of crystals on solid substrates leads to the formation polymers
with a well-defined grafting density (Zhou et al. 2016). Garcia-Mutio et al. (2016)
developed a voltammetric sensor based on MIN ‘grafted to’ the surface of Au electrodes. It was shown that the sensor specifically recognizes 4-ethylphenol on structural analogues (Garcia-Mutio et al. 2016).
As for the ‘grafting from’ approach, an initiator (or even an iniferter) is immobilized on a solid surface in a preliminary step. Then, using controlled polymerization
techniques, the polymer layer grows from the immobilized initiator monolayer. In
this case, the steric repulsion allows the stretching of the chains with the formation
of a brush-type conformation of attached chains. Dong et al. (2018) developed MIP
membranes using the ‘grafting from’ approach via RAFT polymerization. These
authors showed that the adsorption, permeation and separation capability of the
membranes depends on the grafted monomers (Dong et al. 2018). Gao et al. (2018)
also proposed a technique of synchronously, graft/crosslinking polymerization of
monomers and imprinting of templates, on the surface of the chloromethylated
polysulfone, used as a substrate (Gao et al. 2018).
5.4 Techniques for MIP Characterization
A wide range of techniques has so far been useful to carry out the MIP characterization, particularly regarding its binding behavior, morphology and physicochemical
properties. Due to the insoluble nature of most MIP materials, their characterization
is usually limited to methods that do not involve the solution state.
5.4.1 Morphological Characterization
5.4.1.1 Surface Area, Pore Size and Mechanical Properties
Surface area of a MIP particle is considered as the whole external area, including
the surface attributable to pores, and is mainly influenced by the amount of crosslinking monomer, the amount and the type of porogen, as well as the temperature
A. Gómez-Caballero et al.
exposed functional groups of the preformed SAM. This strategy is very simple, but
steric repulsions can occur between the polymer chains, which can prevent the formation of dense polymers. If this happens, polymer chains will not be oriented perpendicularly to the solid surface. It is also particularly difficult to immobilize polymers
having high Mws, since the reaction between the final group of the polymer chain and
the end group on the SAM layer can be hindered (Murugan et al. 2015).
Zhou et al. (2016) reported a new ‘grafting to’ approach called ‘self-assemblyassisted-grafting to’. The key is that, here, the polymers are preassembled into twodimensional polymer single crystals with functional groups on the surface. The
chemical coupling of crystals on solid substrates leads to the formation polymers
with a well-defined grafting density (Zhou et al. 2016). Garcia-Mutio et al. (2016)
developed a voltammetric sensor based on MIN ‘grafted to’ the surface of Au electrodes. It was shown that the sensor specifically recognizes 4-ethylphenol on structural analogues (Garcia-Mutio et al. 2016).
As for the ‘grafting from’ approach, an initiator (or even an iniferter) is immobilized on a solid surface in a preliminary step. Then, using controlled polymerization
techniques, the polymer layer grows from the immobilized initiator monolayer. In
this case, the steric repulsion allows the stretching of the chains with the formation
of a brush-type conformation of attached chains. Dong et al. (2018) developed MIP
membranes using the ‘grafting from’ approach via RAFT polymerization. These
authors showed that the adsorption, permeation and separation capability of the
membranes depends on the grafted monomers (Dong et al. 2018). Gao et al. (2018)
also proposed a technique of synchronously, graft/crosslinking polymerization of
monomers and imprinting of templates, on the surface of the chloromethylated
polysulfone, used as a substrate (Gao et al. 2018).
5.4 Techniques for MIP Characterization
A wide range of techniques has so far been useful to carry out the MIP characterization, particularly regarding its binding behavior, morphology and physicochemical
properties. Due to the insoluble nature of most MIP materials, their characterization
is usually limited to methods that do not involve the solution state.
5.4.1 Morphological Characterization
5.4.1.1 Surface Area, Pore Size and Mechanical Properties
Surface area of a MIP particle is considered as the whole external area, including
the surface attributable to pores, and is mainly influenced by the amount of crosslinking monomer, the amount and the type of porogen, as well as the temperature
A. Gómez-Caballero et al.