Asymmetric Polymerization of N-ortho- or para-Substituted Phenylmaleimide Using Chiral Anionic Initiators

Abstract

ABSTRACT:N-Phenylmaleimide (PhMI) and its derivatives were polymerized using chiral anionic initiators consisting of diethylzinc (Et 2 Zn) and chiral ligands to investigate the effect of the bulkiness, flexibility and polarity of the ortho-or para-substituents on optical activity of the obtained polymer. The optical activity of the polymer was extremely influenced by N-substituents, initiators, and other polymerization conditions. Poly(N-2-biphenylmaleimide) (poly(2-BPMI)) formed with Et 2 Zn-(-)-2,2 -(1-ethylpropylidene)bis(4-benzyl-2-oxazoline) (Bnbox) showed the highest specific rotation ([α] 25 435 ) of +164.7• . From 13 C NMR spectroscopy, optically active poly(2-BPMI) and poly(N-(2-phenoxy)-phenylmaleimide) (poly(2-POPMI)) mainly possessed threo-diisotactic structures in the main chains. Chiral stationary phase prepared from optically active poly(PhMI) optically resolved racemic 1,1 -bi-2-naphthol.KEY WORDS N-Substituted Maleimide / Asymmetric Anionic Polymerization / Chiral Ligand / Optically Active Polymer / N-Substituted maleimide (RMI) is one of the interesting monomers which can form an optically active polymer. [1][2][3][4][5] Main chain carbons of poly(RMI) are chiral because polymerization of RMI proceeds through only trans-opening reaction of double bond in the imide ring. 6 Structures of poly(RMI) produced by trans-addition reactions are displayed in Chart 1. In threo-disyndiotactic structures, stereogenic centers (S , S ) and (R, R) in each monomeric unit equally exist, so that main chain carbons of poly(RMI) do not exhibit optical activity. Threo-diisotactic structures exert optical activity only if either of configurational pairs of (S , S ) or (R, R) predominantly is formed in the trans-main chains. Furthermore, when the same configurational pairs are successively connected in the threo-diisotactic sequences, the polymer main chains can form a helical conformation. If poly(RMI) contains the sequences of helical conformation, the polymer has not only configurational chirality but also conformational one.Systematic research on asymmetric anionic polymerization of achiral RMI bearing aromatic groups has been performed by the authors. 4, 5 Optical activity of poly(RMI) was significantly affected by a structure of N-substituent. The authors investigated the effect of bulkiness of N-substituent on optical activity of poly(RMI) prepared by asymmetric anionic polymerization. = −36.8 • to +762.3 • ) formed by asymmetric anionic method was the highest in all of poly(RMI)s obtained so far. Thus, bulky N-substituents did not always provide high optical activity to the obtained poly(RMI). Therefore, further studies on the effect of N-substituents of RMI on optical activity of the polymer are currently desirable.In this paper, we introduced a substituent into the ortho-or para-position of phenyl group of PhMI, and Chart 1.

Thermal Properties of N-Phenylmaleimide-Isobutene Alternating Copolymers Containing Polar Groups to Form Intermolecular and Intramolecular Hydrogen Bonding

“…[1][2][3] At the same time, various kinds of PhMI derivatives have also been synthesized and polymerized. [4][5][6][7][8][9][10][11][12] When alkyl substituents were introduced in the N-phenyl group, the polymers were soluble in non-polar solvents and showed an excellent thermal decomposition property, while poly(1) was soluble in limited kinds of polar solvents. 13,14 On the other hand, the introduction of polar substituents resulted in the formation of polymers with poor solubility.…”

Asymmetric Polymerizations ofN‐Substituted Maleimides

“…However, the obtained polymers exhibited only a little optical activity ([a] 435 ¼ À7.4 to À2.9 ), indicating that the directly coupled bisoxazolines cannot build a better asymmetric field at the growing polymer end. The absolute values of specific rotations of the poly(RMI) obtained with Et 2 Zn-Bnbox were higher than those of polymers obtained with Et 2 Zn-Sp [31][32][33][34]. In that report, CHMI, PhMI, and TBMI were polymerized using n-BuLi-four-types-methylene-bridged-bisoxazoline-derivative complexes ( Figure 12 However, specific rotations of poly(PhMI), which possesses an aromatic group as the N-substituent, were much smaller ([a] 435 ¼ À18.3 to þ 8.7 ) than those of poly (CHMI) and poly(TBMI), and they employed diethyl zinc (Et 2 Zn) instead of n-BuLi as an organometal.…”

An Overview of Polymer‐Immobilized Chiral Catalysts and Synthetic Chiral Polymers

“…Asymmetric polymerization of achiral N-substituted maleimide also has been investigated [93]. Asymmetric polymerization of achiral N-substituted maleimide also has been investigated [93].…”