Polymer support macroporous

In the next step, the best candidate from the series 2-oxo-4-(9-phenanthryl)-dihy-dropyrimidine 22 was prepared and isolated in enantiomerically pure form, then attached to a macroporous polymer support. To attach the isolated selector to the amino functionalized macroporous polymethacrylate support, a suitable reactive handle had to be introduced into the dihydropyrimidine. We chose to functionalize the methyl group at the C6 carbon atom by a simple bromination to afford (-)-22. Coupling of this compound to the amino functionalized support then gave the desired chiral stationary phase CSP 12 (Scheme 3-6) containing 0.20 mmol g of the selector. 

Tennikov, M. B., Gazdina, N., Tennikova, T. B., and Svec, F., Effect of porous structure of macroporous polymer supports on resolution in high-performance membrane chromatography of proteins, J. Chromatogr. A, 798, 55, 1998. 

Figure 17 Preparation of a macroporous polymer-supported alkoxy-titanate.

As far as polymer supports for microwave-assisted SPOS are concerned, the use of cross-linked macroporous or microporous polystyrene (PS) resins has been most prevalent. In contrast to common belief, which states that the use of polystyrene resins limits reaction conditions to temperatures below 130 °C [14], it has been shown that these resins can withstand microwave irradiation for short periods of time, such as 20-30 min, even at 200 °C in solvents such as l-methyl-2-pyrrolidone or 1,2-dichlorobenzene [15]. Standard polystyrene Merrifield resin shows thermal stability up to 220 °C without any degradation of the macromolecular structure of the polymer backbone, which allows reactions to be performed even at significantly elevated temperatures. 

I 1 Structure, Morphology, Physical Formats and Characterization of Polymer Supports 1.2.3.2 Collapsible Macroporous Resins... 

Still, this theory is over-simplified, and holds only for a limited part of the sorption isotherm, which is usually the case for relative pressures between 0.05-0.30, and the presence of point B (Fig. 1.14). Thus, isotherms of Types II (macroporous polymer supports) and IV (mesoporous polymer supports), but not Type I and III, are those amenable to BET analysis [21, 80]. Attention should also be paid to the constant C, which is exponentially related to the enthalpy of adsorption of the first layer. A negative or high value of C exceeding 200-300, is likely to indicate the presence of micropores and the calculated surface area should be questioned since the BFT theory would not be applicable [79, 80]. 

As discussed in Section 1.4.2.1, the critical condensation pressure in mesopores as a function of pore radius is described by the Kelvin equation. Capillary condensation always follows after multilayer adsorption, and is therefore responsible for the second upwards trend in the S-shaped Type II or IV isotherms (Fig. 1.14). If it can be completed, i.e. all pores are filled below a relative pressure of 1, the isotherm reaches a plateau as in Type IV (mesoporous polymer support). Incomplete filling occurs with macroporous materials containing even larger pores, resulting in a Type II isotherm (macroporous polymer support), usually accompanied by a H3 hysteresis loop. Thus, the upper limit of pore size where capillary condensation can occur is determined by the vapor pressure of the adsorptive. Above this pressure, complete bulk condensation would occur. Pores greater than about 50-100 nm in diameter (macropores) cannot be measured by nitrogen adsorption. 

Another example of a macroporous methacrylate-based polymer support is shown in Fig. 1.19 [101]. Again, only the relevant pore range is displayed. The pores around 1 pm are fully revealed by mercury intrusion, whereas with nitrogen sorption, above 0.1 pm, essentially no pores can be detected. 

In contrast, the use, in chromatography, of poly(trityl methacrylate) appears much more promising. Both the insoluble polymer and macroporous silica gel coated with a soluble polymer have been used. The latter system gives better results, especially with regard to elution time. The columns have proved quite efficient in resolution of a great variety of chiral organic compounds (365, 388). Other examples of usefiil chiral polymer supports are the substituted polyacrylamides (389). Earlier used adsorbents obtained by reacting optically active amines with polyacryloyl chloride have been superseded by new chiral phases prepared by direct polymerization of optically active acrylamides. 

Note 3 The location of active sites introduced into a polymer support depends on the type of polymer support. In a swollen-gel-bead polymer support the active sites are distributed uniformly throughout the beads, whereas in a macroporous-bead polymer support they are predominantly on the internal surfaces of the macropores. 

The first polymer-supported reagents were derived from ion-exchange resins by immobilizing ionic reagents on macroporous polystyrene resins [5], This approach enables easy access to many reagents. For preparation, a... 

Dumartin and associates described the preparation of in situ polymer-supported organ-otin hydrides for use as clean reducing agents (equation 15)47, while Deleuze and coworkers reported the preparation of a novel, macroporous polymer-supported organotin hydride (37), for use in catalytic free-radical reductions (equation 16)48,49. 

An early example for the direct coupling of a tin reagent to Amberlite XE 305, a macroporous polystyrene, was reported by Crosby and coworkers157. The synthetic route is shown in Scheme 35. Reaction of the polymer-supported diorganotin dihydride 70 with iodooctane to give octane indicated a minimum content of 2 mmol tin hydride per gram of the polymer. 

Ahmed and coworkers have developed analogues of 2 and 4 immobilised on PS via the alkylidene moiety. Catalysts 77 [ 124] and 78 [ 125] promoted efficient RCM they could also be recovered (by simple filtration) and recycled several times. Jafarpour and coworkers [ 126] later prepared less-polymer-swelling-dependent analogues 79-81 bound to macroporous PS. We have developed the permanently immobilised catalyst 82, which was the first polymer-supported catalyst reported to be active across a range of metathesis reactions such as RCM, enyne CM and RRM [ 127]. Catalysts which incorporate readily modified... 

Hi. The monomer polymerization route. Compared with the resin-functionalization route, the homo- and copolymerization of organotin-containing monomers permits one to influence the polymer resin structure to a greater extent. In principle, it is possible to prepare gel-type, macroporous, microporous or nonporous polymers. The pore structure, tin loading, solubility and other factors which influence the reactivity of the polymer-supported organotin reagents can be controlled by appropriate... 

For example, polymer-supported CSPs with Pirkle-concept SOs (e.g. (S)-valine-3,5-dimethylaniIide) attached to monodisperse macroporous polymethaciylate beads gave reasonable enantioselectivity and efficiency for 3,5-dinitrobenzamido derivatives of a-amino acids under normal-phase conditions [368.370], It could be demonstrated that such a CSP based on polymeric particles provided enhanced enantioselectivities... 

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