Solution structures, monomer-templates

Also of considerable importance is the mechanism of site formation. At what stage in the polymerisation are the high energy sites formed and stabilised Does the solution structure of the monomer-template assemblies reflect the disposition of functional groups at the binding sites [24] (See Chapter 5 for a further discussion.) Attempts to correlate the association constants determined for the monomer-template interactions in homogeneous solution with the rebinding association... 

It is of obvious importance that the functional monomers strongly interact with the template prior to polymerisation, since the solution structure of the resulting assemblies presumably defines the subsequently formed binding sites. By stabilising the monomer-template assemblies it is possible to increase the number of imprinted sites. At the same time the number of non-specific binding sites will be minimised, since there will be a reduction in the amount of free, non-associated functional monomer. For any particular template, the following factors that are likely to affect the recognition properties of the site have been identified (Fig. 5.14). 

To what extent do the solution complexes formed between the monomer and the template in solution reflect the architecture of the polymeric binding sites This question is important, since a thorough characterisation of the monomer-template assemblies may assist in deducing the structure of the binding sites in the polymer and thus have a predictive value. 

In the self-assembly approach to molecular imprinting (Fig. 7.1) studies have indicated that the solution structure of the monomer-template assemblies defines the subsequently formed binding sites.3 In other words, the amount and quality of recognition sites in the MIP depends on the number and strength of specific interactions occurring between the template and the monomers in the prepolymerisation mixture (Fig. 7.4). These are in turn influenced by the quality of the solvent, cross-linking monomer, temperature, and pressure used in the polymerisation. 

Moreover, efficiency of phase inversion imprinting can be improved with pre-forming complex of monomer-template (Table 2) in copolymerization [70]. The THO-acrylic acid or methacrylic acid precomplex monomer was copolymerized with acrylonitrile in DMSO. The resultant viscous solution contents were used for phase inversion in water after template copolymerization. Template copolymers can improve binding capacity of THO. From H-NMR analysis, this is due to tailor-made modification of a copolymer backbone for the template molecule. Also, comparison was made between copolymers of acrylic acid and methacrylic acid in THO selectivity of the imprinted polymers. Presence of the methacryl methyl group is more efficient in the tailor-made structure of the THO template. 

Certain factors such as temperature, solvent and solvent-to-head-space ratio play an important role in the formation of a crystalline framework [66]. Certain solvents can be employed in order to form ordered networks by means of their ability to dissolve the monomer building blocks. If the concentration of a monomer in solution is controlled by a solvent in which it is slightly soluble, then a network is more likely to form under thermodynamic, instead of kinetic control [68]. Solvents could also be used based on their molecular size to act as templates for pores to form around [69], While this idea of MOP/COF templating is generally understood in qualitative terms (which solvents produce crystalline networks) there has been no research into the quantitative effects (what solvent ratio is required to produce a well-structured network). 

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