Molecularly imprinted polymers polymerization

The sorbents that are most frequently used in environmental analysis are Cig-silica based sorbents, polymeric sorbents (usually styrenedivinilbenzene) and graphitized carbon. In order to increase the selectivity of these sorbents, immunosorbents (35, 36) have been developed and used with good results, while recently, molecularly imprinted polymers have started be to used (35, 36). 

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

Molecularly imprinted polymers have recently attracted much attention because they are denoted as artificial antibodies which are made from simple chemical components via polymerization and can be used for the preparation ofbiomimetic sensors, affinity separation matrices, catalysts, etc. (Figure 1). 

HaU AJ, AchiUi L, Manesiotis P, Quaglia M, De Lorenzi E, SeUergren B. A substructure approach toward polymeric receptors targeting dihydrofolate reductase inhibitors. 2. Molecularly imprinted polymers against Z-L-glutamic acid showing affinity for larger molecules. J Org Chem 2003 68 9132-9135. 

Piletsky SA, Piletska EV, Karim K, Freebaim KW, Legge CH, Turner APR Polymer cookery influence of polymerization conditions on the performance of molecularly imprinted polymers. Macromolecules 2002 35 7499-7504. 

Titirici MM, Sellergren B. Thin molecularly imprinted polymer films via reversible addition-fragmentation chain transfer polymerization. Chem Mater 2006 18 1773-1779. 

Figure 20-23 (a) Surface plasmon resonance spectrum of sensor coated with molecularly imprinted polymer that selectively binds NAD+. (b) Response of sensor to four similar molecules shows largest response to NAD+, which was the template for polymerization. [From O. A. Raitman. V. I. Chegel, a B. Kharitonov. M. Zayats. E. Katz, and I. Winner. Analysis of NAD(P) and NAD(P)H Cofactors by Means of Imprinted Polymers Associated with Au Surfaces A Surface Plasmon Resonance Study. Anal. CNm. Ada 2004,504. 101.]... 

A molecularly imprinted polymer is one that is polymerized in the presence of a template molecule to which components of the polymer have some affinity. When the template is removed, the... 

Keywords Artificial receptors Molecularly imprinted polymers Plastic antibodies Protein imprinting Water compatible MIP Controlled/living radical polymerization... 

A wide variety of polymeric membranes with different barrier properties is already available, many of them in various formats and with various dedicated specifications. The ongoing development in the field is very dynamic and focused on further increasing barrier selectivities (if possible at maximum transmembrane fluxes) and/ or improving membrane stability in order to broaden the applicability. This tailoring of membrane performance is done via various routes controlled macro-molecular synthesis (with a focus on functional polymeric architectures), development of advanced polymer blends or mixed-matrix materials, preparation of novel composite membranes and selective surface modification are the most important trends. Advanced functional polymer membranes such as stimuli-responsive [54] or molecularly imprinted polymer (MIP) membranes [55] are examples of the development of another dimension in that field. On that basis, it is expected that polymeric membranes will play a major role in process intensification in many different fields. 

Molecularly imprinted polymers with a variety of shapes have also been prepared by polymerizing monoliths in molds. This in situ preparation of MIPs was utilized for filling of capillaries [20], columns [21], and membranes [22, 23]. Each specific particle geometry however needs optimization of the respective polymerization conditions while maintaining the correct conditions for successful imprinting. It would be advantageous to separate these two processes, e.g., to prepare a molecularly imprinted material in one step, which then can be processed in a mold process in a separate step to result the desired shape. 

Mosbach and co-workers developed a method to prepare molecularly imprinted polymers by precipitation polymerization [24]. They started from a dilute, homogenous solution of the monomer methacrylic acid (MAA) and the crosslinker trimethylolpropane trimethacrylate (TRIM) or ethylene glycol dimethacrylate (EGDMA). The polymer formed in the presence of the template molecule 17/1-estradiol, theophylline, or caffeine contained a high proportion of discrete spheres of diameter less than a micron. Because the effect of coalescence becomes predominant with higher solid content of the reaction mixture, this approach is limited to solid contents of typically <2 wt%. 

Molecularly imprinted polymers (MIPs) allow for predetermined selectivity of enantiomers. MIPs are prepared by polymerizing a mixture of functional mono-mer(s) and cross-linking monomer in the presence of a template molecule. The template molecule remains in a pocket by its interaction with a functional monomer through hydrogen bonding. This allows the MIP to be found at the surface of the polymer. When polymerization is complete and the template molecule is removed, the polymer remembers the template molecule. 

Polymer libraries are covered according to their numerous applications, each described through a specific example. The reported examples include libraries of copolymers as liquid/solid supports with different compositions, libraries of biodegradable materials for clinical applications, libraries of stationary phases for GC/LC separations, libraries of polymeric reagents or catalysts, libraries of artificial polymeric receptors or molecularly imprinted polymers, and libraries of polymeric biosensors. The opportunities that could arise in the near future from novel applications of polymer libraries are also briefly discussed. 

Figure 11.24 Molecularly imprinted polymers (MIP) random (top) and template-assisted (bottom) polymerization process.

The basic concepts in forming a molecularly imprinted polymer are therefore rather simple. Indeed this apparent simplicity has misled some would-be users of this approach who have failed to appreciate that realising this in practice, particularly with any degree of efficiency, has proved enormously difficult. Not the least, most polymer chemists would appreciate that to produce a crosslinked polymeric network sufficiently rigid to retain some memory of an imprint molecule, and yet allow ready mass transfer of molecules to and from the memory cavities, is no small undertaking. The early workers in the field have made enormous efforts to bring the technique to a point where materials capable of application and exploitation are now becoming available, and this is as much a tribute to their tenacity as it is to their scientific invention. 

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