Anionic polymer, helical

A chiral PDBSMA derivative, IDPDMA (26), was designed to form a single-handed helical polymer through radical polymerization due to the effect of the chirality in the side chain.83 The anionic polym-... 

Interestingly, Reggelin et al. [147] prepared helical chiral polymers by helix-sense selective anionic polymerization of methacrylates, using an asymmetric base mixture as initiator (Scheme 61). 

Polymerization of triphenylmethyl methacrylate in the presence of a chiral anion catalyst results in a polymer with a helical structure that can be coated onto macroporous silica [742,804). Enantioselectivity in this case results from insertion and fitting of the analyte into the helical cavity. Aromatic compounds and molecules with a rigid nonplanar structure are often well resolved on this phase. The triphenylmethyl methacrylate polymers are normally used with eluents containing methanol or mixtures of hexane and 2-propanol. The polymers are soluble in aromatic hydrocarbons, chlorinated hydrocarbons and tetrahydrofuran which, therefore, are not suitable eluents. 

A bulky methacrylate, triphenylmethyl methacrylate (TrMA), is a unique monomer which gives an almost 100% isotactic polymer in anionic polymerization with n-butyllithium both in nonpolar and polar solvents. Moreover, even free-radical polymerization affords a highly isotactic polymer from this monomer.23 The isotactic specificity of TrMA polymerization is ascribed to the helical formation of the main chain. When TrMA is polymerized in toluene at —78°C... 

Compound 72 was shown to display enantioselectivity in the extraction of chiral potassium salts from water into the organic phase.105 The supramolec-ular polymer possesses a homochiral helical architecture onto which one of the anionic enantiomers preferentially binds. Intriguingly, for some of the anions the octamer and polymer showed opposite selectivity, illustrating the difference in supramolecular chirality of the two systems. Furthermore, the polymer was capable of inducing a Cotton effect in the achiral compound potassium A-(2,4-dinitrophenyl)glycinate. Since the apolar side chains would... 

Another interesting chiral chain end effect is exhibited by the helical polymer block co-polymer, poly(l,l-dimethyl-2,2-di-/z-hexylsilylene)- -poly(triphenylmethyl methacrylate), reported by Sanji and Sakurai (see Scheme 7) and prepared by the anionic polymerization of a masked disilene.333 The helical poly(triphenylmethyl methacrylate) block (PTrMA) is reported to induce a PSS of the same sign in the poly(di- -propylsilylene) block in THF below — 20 °C, and also in the solid state, by helicity transfer, as evidenced by the positive Cotton effect at 340 nm, coincident with a fairly narrow polysilane backbone UV absorption characteristic of an all-transoid-conformation. This phenomenon was termed helical programming. Above 20°C, the polysilane block loses its optical activity and the UV absorption shifts to 310 nm in a reversible, temperature-dependent effect, due to the disordering of the chain, as shown in Figure 45. 

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. 

Anionically formed polymers of /3-Iactones have helical macrostructures, in which the ester groups are approximately in the planar configuration. Copolymers of different /3-lactones have the same basic structure but show variations of other properties (73AG(E)432, 77MI51301, 78MI51302, 74CJC3742). 

Recently, we found that the polymerization of TrMA with chiral anionic catalysts gave an optically active polymer the chirality of which is caused by helicity (12). This is the first example of optically active vinyl polymer the activity of which arises only from the helicity. This article describes the detailed results of the polymerization of TrMA by chiral anionic catalysts in addition to a brief review on our earlier studies described above. 

In conclusion, the reality of helical growth, which was proposed by Lundberg and Doty, seems to be proved beyond any doubt. In fact, these phenomena may play an important role in other polymerising systems. Szwarc (91) suggested that the results of Williams et al. (92), who studied anionic polymerisation of styrene in different solvents, may be explained in terms of a helical growth, and a similar suggestion was made by Ham (93) to account for peculiarities some radical polymerisations.Well-documented studies of anionic polymerisation of methyl methacrylate (94) lead to the conclusion that random-coiled polymers, as well as helices, may participate in this reaction. This subject has been fully reviewed in a recent publication (95). 

Anionic Catalysis Several bulky methacrylates afford highly isotactic, optically active polymers having a single-handed helical structure by asymmetric polymerization. The effective polymerization mechanism is mainly anionic but free-radical catalysis can also lead to helix-sense-selective polymerization. The anionic initiator systems can also be applied for the polymerization of bulky acrylates and acrylamides. The one-handed helical polymethacrylates show an excellent chiral recognition ability when used as a chiral stationary phase for high-performance liquid chromatography (HPLC) [97,98]. 

Aldehyde Polymers Asymmetric anionic polymerization can lead trichloroacetalde-hyde (chloral) to a one-handed helical, isotactic polymer having a 4/1-helical conformation with... 

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