Trityl methacrylate

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 Earlier used adsorbents obtained by reacting optically active amines with polyacryloyl chloride have been superseded by new chiral phases prepared by direct polymerization of optically active acrylamides. 

A polymerization of a bulky methacrylate ester (e.g. trityl methacrylate) using an optically active anionic initiator can give an isotactic polymer, poly 1-methyl-1-[(trityloxy)carbonyl]ethylene of high optical activity owing to the formation of helical polymer molecules with units of predominantly one chirality sense. 

Fractionation of Copoly(Methyl Methacrylate-Methacrylic Acid) Obtained by Hydrolysis of Copoly(Methyl Methacrylate- Trityl Methacrylate)... 

S. Kanoh, H. Suda, N. Kawaguchi, and M. Motoi, Makromol. Chem., 187, 53 (1986) G. Wulff, B. Vogt, and J. Petzoldt, New Aspects of the Asymmetric Polymerization of Trityl Methacrylate, Polymeric Materials Science and Engineering, Vol. 58, p. 859, American Chemical Society, Washington, D.C., 1988. 

Preparative enrichment of enantiomers should be followed by determination of their chemical and enantiomeric purities, e.g., by enantioselective liquid chromatography.25,26 In addition to the sorbents mentioned above, others may be used which are available in only smaller amounts. In our laboratory, this is true for (+)-poly(trityl methacrylate) on silica,35 which can be used for analytical purposes. Preparative separations on a column 0.5 cm in diameter, however, would require many injections of small amounts of racemate. In the case of a baseline chromatogram like that in Figure 2, the determination of enantiomeric purity by measurement of the two peak areas of the enantiomers is straightforward. An analytical chromatogram showing some separation by photometric detection in spite of peak overlap (Figure 4) can still be used for optical purity determina-tion. The simultaneous use of both photometric and chiroptical detection as... 

The combination of organolithiums with chiral coordination ligands such as sparteine allows the asymmetric polymerization to furnish optically active polymers with very high enantioselectivity. especially when trityl methacrylate is utilized as a monomer [13, 14]. 

Optically active synthetic polymers such as poly(trityl methacrylate) supported on silica gel [7,8] as well as poly(ethylene glycol dimethacrylate) cross-linked in the presence of an optically active template [9] have found general use as chiral stationary phases for the optical resolution of various racemates by chromatography. A current area of investigation concerns the use of optically active polymers as reagents and catalysts for asymmetric synthesis [10,11,12]. 

During the two decades after this important discovery, a tremendous amount of research has been directed toward the polymerization of sterically demanding achiral monomers with chiral initiators to create enantiomerically pure helical polymers (also known as helix-sense selective or screw-sense-selective polymerization ). These polymers, known as atropisomers, are stable conformational isomers that arise from restricted rotation about the single bonds of their main chains. Key aspects of these reactions are enantiopure initiators that begin the polymerization with a one-handed helical twist, and monomers with bulky side-chains that can maintain the helical conformation due to steric repulsion. Notable examples of this fascinating class of polymers that are configurationally achiral but conformationally chiral include [8, 38, 39] poly(trityl methacrylate), polychloral, polyisocyanates, and polyisocyanides. Important advances in anionic and metal-based enantioselective polymerization methods have been reported in recent years. 

Yamada and Tanaka reported that the best fit was attained assuming Oi2 = O21 = Voi j O22 = 0.41 for the radically prepared copolymers of methyl methacrylate and trityl methacrylate. ... 

Similarly the coisotactic parameters were obtained in the copolymerizations between methyl methacrylate(Mi) with other methacrylates(M2), and between OK-methylbenzyl methacrylate(Mi) with trityl methacrylate(M2) by radical and BuLi initiators in THF. The parameters are shown in Table 20. 

On the other hand, the copolymerization of (S)-a-nieth benzyl methacrylate (Ml) and trityl methacrylate(M2) by Buli in toluene yielded a mixture of an isotactic polytiBr of Ml and a less stereoregular copdymer, similady to the copdy-merization of methyl methacrylate(Mi) and trityl methacrylate(M2) in this solvent. If the (RS)-monomer was used instead of (S)-isomer, only the copdymer of low stereoregularity was produced, althou it had a wide distribution as to the composition. The low reactivity of trityl methacrylate in the copdymerization even with (RS)-o-methylbenzyl methacrylate may be also attributed to the sterk hindrance due to the bulkiness of the trityl ester, since the homopdymerization of this monomra itself proceeded extremely slowly in toluene. ... 

Table 21. Anionic copolymerization of (S)-o -methylbenzyl methaarylate(Mi) and trityl methacrylate(M2) by BuLi in THF at -78... 

Electron-withdrawing substituents in anionic polymerizations enhance electron density at the double bonds or stabilize the carbanions by resonance. Anionic copolymerizations in many respects behave similarly to the cationic ones. For some comonomer pairs steric effects give rise to a tendency to altemate. The reactivities of the monomers in copolymerizations and the compositions of the resultant copolymers are subject to solvent polarity and to the effects of the counterions. The two, just as in cationic polymerizations, cannot be considered independently from each other. This, again, is due to the tightness of the ion pairs and to the amount of solvation. Furthermore, only monomers that possess similar polarity can be copolymerized by an anionic mechanism. Thus, for instance, styrene derivatives copolymerize with each other. Styrene, however, is unable to add to a methyl methacrylate anion, though it copolymerizes with butadiene and isoprene. In copolymerizations initiated by w-butyllithium in toluene and in tetrahydrofuran at-78 °C, the following order of reactivity with methyl methacrylate anions was observed. In toluene the order is diphenylmethyl methacrylate > benzyl methacrylate > methyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > t-butyl methacrylate > trityl methacrylate > a,a -dimethyl-benzyl methacrylate. In tetrahydrofuran the order changes to trityl methacrylate > benzyl methacrylate > methyl methacrylate > diphenylmethyl methacrylate > ethyl methacrylate > a-methylbenzyl methacrylate > isopropyl methacrylate > a,a -dimethylbenzyl methacrylate > t-butyl methacrylate. 

Since a comprehensive review [28] was completed in 2001, every effort will be made not to duplicate this tome. Additionally, 3-peptides have been the subject of several reviews and will be mentioned more briefly than they warrant. Other recent reviews have covered oligoarylamides [29], a brief review of foldamers in general [30], and an article [31] focusing on the secondary structure aspect of foldamers. We will not include polymers like polyphenyl acetylene derivatives, polyisocyanides, and poly(trityl methacrylates) in which the conformations are dominated by nearest neighbor steric interactions, although these macromolecules represent very interesting systems that seem to adopt a limited number of the available conformations in solution [32-35]. 

Yuki et al. demonstrated that trityl methacrylate (TrMA) initiated... 

One of us (MAD) wishes to acknowledge support for this work by the University of Florida, Division of Sponsored Research, through a research assistant ship. We also wish to thank Professor Y. Okamoto for making available to us the synthetic procedures for the preparation of trityl methacrylate. 

An analogous case is offered by the copolymers between optically active [(S)-a-methyIbenzyll-methacrylate and trityl-methacrylate [30 ] (Figure 8), the optical activity of which varies with composition turning from negative to positive when the content of trytilmethacrylate units overtalces 80 mole. 

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