Choice of the functional monomer

Apart from the successful examples discussed above, the recognition for many templates is far from that required for the particular application, even after careful optimisation of the other factors affecting the molecular recognition properties. Often, a large excess of MAA in the synthesis step is required for recognition to be observed and then only in solvents of low to medium polarity and hydrogen bond capacity [68]. In fact, in these cases the optimum rebinding solvent is often the solvent used as diluent (see under Section 5.7.) [69]. Thus the polymer exhibits 

Based on the structural features of the templates that generate good sites, an interesting possibility would be to incorporate these structures in new functional monomers for the recognition of carboxylic acids. This concept is somewhat similar to the reciprocity concept in the design of CSPs [70]. Thus Wulff et al. synthesised A,A -disubstituted p-vinylbenzamidines (see 13 in Table 5.6B) and showed that these monomers could be used to generate high fidelity sites for the molecular 

ACIDIC FUNCTIONAL MONOMERS GIVING ENHANCED REBINDING SELECTIVITY IN NON-COVALENT MOLECULAR IMPRINTING 

Trifluoromethyl acrylic acid (TFM) SCHa 1 1 H H Prometryn (PRO) Enhanced selectivity in lerpolymer with MAA [87] 

AjgX S03H Acrylamidomethylpropane sulfonic acid (AMPSA) 0 2,6-diaminoantraquinone bio selectivity seen using MAA as functional monomer [154] 

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A broad range of functional monomers and cross-linkers has been used for the preparation of MIPs. The choice of the functional monomers depends on the nature and functionalities of the print molecule. The most widely used monomer is methacrylic acid, which has been shown to interact through ionic interactions and hydrogen bonds with amines, amides, carbamates and carboxylic acids [13-15]. The monomers and the print molecules self-assemble upon mixing and the strength of the complex is of importance for the selectivity of the polymer. For this reason, a considerable amount of research effort has focused on finding optimal monomers for various classes of print molecules and functionalities. For example, for some print molecules, polymers prepared with vinylpyridines [16,17], 2-(trifluoromethy-l)acrylic acid [18] or acrylamide [19] resulted in higher selectivities and affinities than polymers made from methacrylic acid. Mixtures of functional monomers... 

In case of covalent interactions the choice of the functional monomer, which has to be linked covalendy to the template prior to imprinting, depends on the chemistry of the template. Templates containing cis-diol groups are usually esterified with a vinyl-boronic acid component to yield a reversible bis-ester. If this is not possible, alternatives are the generation of Schiff-bases (azomethines). This requires an amino group on the template and a carboxyl acid group on the functional monomer or vice versa (Table 7.2). 

Radiation grafting [83, 84, 85, 86, 87, 88, 89] is a very versatile and widely used technique by which surface properties of almost all polymers can be tailored through the choice of different functional monomers. It covers potential applications of industrial interest and particularly for achieving desired chemical and physical properties of polymeric materials. In this method, the most commonly used radiation sources are high-energy electrons, y-radiation, X-rays, U.V.-Vis radiation and, more recently, pulsed laser [90], infrared [91], microwave [92] and ultrasonic radiation [93]. Grafting is performed either by pre-irradiation or simultaneous irradiation techniques [94, 95]. In the former technique, free radicals are trapped in the inert atmosphere in the polymer matrix and later on the monomer is introduced into... 

The purpose of the functional monomer is twofold. Firstly, it undergoes regiospecific, weak, complementary, interaction with a particular moiety of the template molecule. Secondly, it contains a polymerisable unit. The choice of functional monomer should therefore be based upon the functionality of the molecule to be imprinted. 

E) F unctionalization of membranes - Membranes containing functional groups, which dominate their choice and use as reactive materials, are made by (a) polymerizing styrene-divinylbenzene in sheet-shaped molds followed by further chemical reactions for incorporation of the active species, (b) copolymerization of the functionalized monomer with divinylbenzene in thin film form, and (c) mechanically incorporating powdered functionalized polymer into a sheet of some other extrudable or moldable matrix [77-82]. 

A pair correlation function (r) may be de ed as follows. We pick one monomer at randoni in the chain, and we place it at the origin. Then we ask, what is the number density of other monomers at a distance r from the frrst, and we average the result over all choices of the frrst monomer. The Fourier transform of g(r)... 

By using monomers with different substituents, multiple functionalities could be introduced into the phenylacetylene oligomer at any desired position along the sequence backbone, resulting in macrocycles with a wide variety of symmetries (e.g. 47-53). In principle, this versatile synthetic method should allow construction of PAMs in which anyparticular group couldbe placed at any particular site. Judicious choice of the type and placement of functionalities has... 

For this reaction, soluble monomers are needed, e.g. a mixture of N AT-methylene bisacrylamide as crosslinker, methacrylamide as an inert comonomer, methacrylic acid as ionic comonomer for stabilization [309] and methacryl ami-do-AT-acetaldehyde-dimethylacetal as functional comonomer. The coupling with proteins is only possible if the free aldehyde groups are accessible, i.e. if they are not located in the interior of the microgel. This condition can only be fulfilled by a careful choice of the comonomer composition in the reaction mixture [291]. 

Both methods require that the polymerization of the first monomer not be carried to completion, usually 90% conversion is the maximum conversion, because the extent of normal bimolecular termination increases as the monomer concentration decreases. This would result in loss of polymer chains with halogen end groups and a corresponding loss of the ability to propagate when the second monomer is added. The final product would he a block copolymer contaminated with homopolymer A. Similarly, the isolated macroinitiator method requires isolation of RA X prior to complete conversion so that there is a minimum loss of functional groups for initiation. Loss of functionality is also minimized by adjusting the choice and amount of the components of the reaction system (activator, deactivator, ligand, solvent) and other reaction conditions (concentration, temperature) to minimize normal termination. 

Finally, the most likely value of x in the CPs of interest here is about 2.5 eV or less. Therefore, an ohmic contact for electrons should have a work function of at most 3 eV. This is the case for the alkali metals from Li (2.9 eV) to Cs (2.15 eV) these elements are also, for the same reason, good n-dopants of the CPs slight diffusion into the polymer may then generate an n+ contact favorable for electron injection. The most widely used low-work-function cathode in CP EL is, however, Ca (2.9 eV) [269]. One could try to increase x by a proper choice of the monomer chemical structure, but unless one succeeds in avoiding having Eg reduced simultaneously, the emission will be shifted to the red part of the spectrum. 

Other properties that are heavily influenced by the choice of monomer include cure speed (in general higher functional monomers cure more rapidly), viscosity, and durability of the film. Table 1 lists some monomers, their viscosities, and the properties that they enhance (reprinted with permission from Sartomer). it is important to note several trends on the chart. Cure speed increases with an increase in functionality (all of the recommended monomers in that column are at least trifunctional and several are tetra- or penta-functional). Viscosity also increases as the functionality of the monomer is raised (all of the low viscosity diluents are diacrylates). The adhesion promoting monomers are all di- or mono-functional. Most formulas contain several different monomers and sometimes also oligomers as there is often a balancing act that must be performed when selecting materials that will provide the required performance properties while still maintaining the correct viscosity and surface tension. 

The molecular imprinting technique, based upon a self-association of molecules to build up a binding site structure, requires an appropriate choice of the building blocks, e.g. functional monomers. Construction and screening of imprinted... 

The template, the functional monomers and the cross-linking monomers are dissolved in a non-polar solvent. The functional monomers and the template form complexes and the strength of these are reflected in the selectivity of the imprinted polymer. The choice of functional monomer is based on the template structure. Functional monomers are chosen for their ability to interact non-covalently with the template molecule. The most frequently used functional monomer so far is methacrylic acid (MAA). Also vinylpyridines have been frequently used. As cross-linking monomers, ethyleneglycol dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM) are widely used. Several other types of functional and cross-linking monomers have been used in molecular imprinting experiments using the non-covalent approach. The choice of monomers is of course important to the... 

An important aspect of polymerization is the ability to obtain different products from the same monomer by proper choice of catalyst and reaction conditions. These products may differ in stereochemical configuration or in the nature of the repeating unit. For example, it has been possible to polymerize selectively one or all of the functional groups of polyfunctional monomers. A subject of particular fascination has been... 

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