Functional monomers basic

Considering functional group complementarity, other commodity monomers may also be used. Thus for templates containing acid groups, basic functional monomers are preferably chosen. The 2- or 4-vinylpyridines (VPY) are particularly well-suited for the imprinting of carboxylic acid templates and provide selectivities of the same... 

Fig. 6-10. Influence of the number of basic interaction sites of the template versus the separation factor measured in chromatography for the corresponding racemate. The templates were imprinted using MAA as functional monomer by thermochemical initiation at 60/90/120 °C (24 h at each temperature) and using acetonitrile as porogen. (From Sellergren et al. [15].)...

The initiator used is important for copolymerizations between monomers containing different polymerizing functional groups. Basic differences in the propagating centers (oxonium ion, amide anion, carbocation, etc.) for different types of monomer preclude some copolymerizations. Even when two different monomer types undergo polymerization with similar propagating centers, there may not be complete compatibility in the two crossover reactions. For example, oxonium ions initiate cyclic amine polymerization, but ammonium ions do not initiate cyclic ether polymerization [Kubisa, 1996]. 

Chiral cation exchangers are rarely reported. However, the dominance of an ion-exchange retention model could be established by Sellergren and Shea for an acidic-imprint type CSP that was prepared from methacrylic acid as functional monomer and basic phenylalanine-anilide as oppo.sitely charged template, (1). 380. Maxima in retention were observed at pH-values close to the (apparent) pKa-value of the solutes... 

In this context other commodity monomers may also be used. Thus, for templates containing acid groups, basic functional monomers are preferably chosen... 

BASIC AND CHARGED FUNCTIONAL MONOMERS GIVING ENHANCED REBINDING SELECTIVITY IN NON-COVALENT MOLECULAR IMPRINTING... 

This mode is seen for templates with protolytic functional groups, i.e. Bronsted-basic or acidic groups. In the case where, respectively, an acidic (i.e. MAA) or basic (i.e. VPY) functional monomer is used in the preparation of the corresponding MIPs, the polymeric phases often show good chromatographic performance and excellent selectivity in aqueous mobile phases, where the retention is driven by ion exchange [129]. 

MAA and the stronger acid TFM as functional monomers.5 The polymers were different in the used molar ratio of total functional monomer to template and the molar ratio of MAA to TFM. The polymer library was subjected to a competitive binding experiment by incubating each member with an equimolar mixture of ametryn and atrazine. The templates exhibited a different preference for the two monomers. Although the more weakly basic chlorotriazine prefered the weaker acid MAA, ametryn was best imprinted using TFM as functional monomer. 

The polymerization of ether and thioether monomers was also studied, and it was found that the rate of polymerization was a great deal slower with the functionalized monomers. The number of methylene units between the olefin and the heteroatom greatly affected the rates observed, giving credence to the chelation effect shown in Fig. 6.1. In addition, catalyst 2 polymerizes 1,5-hexadiene, whereas catalyst 6 mainly cyclizes the metathesis dimer to cyclo-l,5-octadiene. At this point there is no clear explanation for this result, and, furthermore, the reason that the COD generated did not undergo ROMP in these reactions is unclear. The data from these experiments clearly shows that Lewis basic functionality retards the rate of metathesis with complex 6 more than with complex 2, although 6 is clearly the more functional group-tolerant complex overall [35]. 

Essentially, the same basic protocol can be adapted for the preparation of non-covalently imprinted polymers. In this case, the cholesterol template monomer is replaced by the template to be imprinted and additional functional monomer (or monomers) is included in the polymerization mixture, at a predetermined molar ratio with respect to the template. Typical functional monomers might be chosen from amongst methacrylic acid, itaconic acid, vinylpyridine, dimethylaminoethyl methacrylate, acrylamide, hydroxyethyl methacylate, and many more. Typical solvents for non-covalent imprinting Include chloroform, THF, and acetonitrile. Templates are removed from non-covalently imprinted polymers by exhaustive washing with a suitable solvent. 

These data indicate that the rate constants of reactions between various monomers and model active species, both ionic and covalent are the function of monomer basicity on the other hand no correlation between ring strain and reactivity was found (44). 

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