Examples of Template Copolymerization

There are also reports of template effects on reactivity ratios in copolymerization. For example, Polowinski20S has reported that both kinetics and reactivity ratios in MMA-MAA copolymerization in benzene arc affected by the presence of a PVA template. 

GPC is a promising method for examination of template polymerization, especially copolymerization. Copolymerization of methacrylic acid with methyl methacrylate in the presence of polyCdimethylaminoethyl methacrylate) can be selected as an example of GPC application for examination of template processes. The process was carried out in tetrahydrofurane as solvent at 65°C. After proper time of polymerization, the samples were cooled, diluted by THF, filtered, and injected to GPC columns. Two detectors on line UV and differential refractometer, DRI, were applied. UV detector was used to measure concentration of two monomers, while the template was recorded by DRI detector (Figure 11.3) The decrease in concentration ofboth monomers can be measured separately. It was found that a big difference in the rate of polymerization between template process and blank polymerization exists. The rate measured separately for methacrylic acid (decrease of concentration of methacrylic acid in monomers mixture) was much higher in the template process. Furthermore, the ratio ofboth monomers changes in a different manner. Reactivity ratios for both monomers can be computed. Decrease in concentration during the process is shown in Figure 11.4. 

Borovik and co-workers (29-31) developed porous organic materials for reversible binding of CO, O2, and NO by means of gas chemical coordination to the metal centers. For immobihzation of metal centers, templated copolymerization was employed (Fig. 7). Material 14, for example, contained immobilized four-coordinate Co(II) centers, and the cobalt concentration ranged from 180 to 230 mol g with an average pore diameter of 25 A (31). Polymer 14 bound NO in toluene solution and even on the air-solid interphase, but was relatively inert toward other biologically important gases O2, CO2, and CO. Nitric oxide could be slowly released from 14 under ambient conditions. For example, after 30 days 80% of NO was lost. Heating the sample accelerated the gas release. 

It seems that the template effect can be pronounced only if interactions between at least one of the monomers is sufficiently strong. Examples of the systems in which one or both monomers were connected with the template by covalent bonds have been described (73-78). Copolymerization of multimonomers similar to the oligomers described by Kammerer with styrene leads to semiladder copolymers, and after hydrolysis to short-block copolsrmers (73). 

The next example deals with copolymerization of MAA with styrene in the presence of PEG. ° It was assumed that, in this case, only MAA can interact with the template. 

On the basis of these examples, we can see that using templates connected by covalent bonds, we can produce a new class of copolymers - semi-ladder block copolymers -with blocks of ladder-type structure. By hydrolysis, the template can be removed and block copolymers with defined length of block can be obtained. Such synthesis by conventional copolymerization is very difficult and sometimes impossible. 

A second method that has been described as a means to deal with the limited accessibility issue involves a copolymerization route. In this approach, the porous matrix is copolymerized with the template. Burleigh and coworkers, for example, described the preparation of imprinted polysilsesquioxanes for the recognition of metal ions.79 Polysilsesquioxanes are hybrid porous materials synthesized from bridged alkoxide precursors such as shown in Figure 20.2.80 In this example, the bridged silsesquioxane precursors were copolymerized with the metal ion complex in the presence of surfactant. Once the surfactant and metal ion were removed, a porous network was formed that showed a high affinity for the metal ion.79... 

Another hybrid MIP example is represented by the copolymerization of phenol with a covalently constructed complex between 3-hydroxyphenyl boronic acid (functional monomer) and monosaccharide (template). The copolymer was deposited on a gold electrode by cyclic voltammetry using two successive scans [46]. The obtained polymer presented an irregular morphology with an average thickness of 36 nm. 

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