Chiroptical Properties of Oligomers of m-Methylphenyl Isocyanate Bearing an Optically Active End-Group

Maeda, Katsuhiro; Matsuda, Masashi; Nakano, Tamaki; Okamoto, Yoshio

doi:10.1295/polymj.27.141

Cited by 44 publications

(25 citation statements)

References 10 publications

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“…The specific rotation of the oligomers of mMeOPI and 3,5MePI increased with an increase in DP in the range of DPs 13 and DPs 15, respectively. As described in the previous report, 11 this is probably because in these DP ranges the oligomers have no helix 102 reversal point and the helical structure becomes stiffer as the DP increases because the vicinity of polymer chain ends should have a higher mobility than the interior of a polymer chain and this effect of the chain ends should be reduced as the DP increases. The gradual decrease of the specific rotation in the higher DP range may be caused by the helix reversal in the main chain.…”

Section: Resultsmentioning

confidence: 59%

“…We already reported that in the mMePI oligomers helix reversal starts from DP= 13. 11 From these results, it is clear that 3,5MePI oligomers which have an additional methyl group at the meta position of mMePI oligomers start to have helix reversals at higher DP than the mMePI oligomers; in other words, poly(3,5MePI) has a longer average persistence length of a helical structure than poly(mMePI). Both electronic and steric factors of the substituents introduced on the phenyl group may affect the persistence length of the helical structure of these oligomers.…”

Section: Resultsmentioning

confidence: 91%

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Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Maeda

1998

Polym J

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ABSTRACT:Oligomerization of phenyl isocyanate derivatives, such as m-methoxyphenyl isocyanate (mMeOPI), 3,5-dimethylphenyl isocyanate (3,5MePI), and m-chlorophenyl isocyanate (mClPI), bearing a substituent at meta position was carried out by using the lithium amide (Li-( -)-MMP) of (S)-( -)-2-(methoxymethyl)pyrrolidine as an initiator to obtain the oligomers containing an optically active group at the initial chain end (()(-end). When the reaction was terminated with HCl-methanol, the oligomers of various degree of polymerization (DP) were isolated for mMeOPI and 3,5MePI, but were not for mClPI. However, oligo(mClPl)s were obtained when the reaction was terminated with acetic anhydride to introduce an acetyl group at the w-end. The obtained oligomers were separated in terms of DP using supercritical fluid chromatography (SFC) and the specific rotation of each oligomer was estimated. The highest specific rotation [0(]~~5 was observed at DP= 13-14 for oligo(mMeOPI), DP= 15 for oligo(3,5MePI), and DP= 10 for oligo(mClPI). These results suggest that the one-handed helical structure can persist to a longer distance as the electron-donating power of the meta substituents increases.KEY WORDS Oligomer / Ary! Isocyanate / Optically Active Polymer / Helix / Anionic Polymerization / Supercritical Fluid Chromatography / Poly(alkyl isocyanate)s are known to have a dynamic helical structure in solution due to the partial double bond character of a main chain and the steric repulsion between main chain carbonyl groups and side chains. 1 -3 Since helix reversals of the polymer chain occur extremely fast, the asymmetric synthesis of an optically active polyisocyanate possessing a rigid completely singlehanded helical structure has not yet been achieved. However, the introduction of a small amount of a chiral component into a polymer chain can induce a prevailing helical structure for poly(alkyl isocyanate)s because of the long persistence length of the helices. Such examples can be seen for the copolymers of an achiral isocyanate with a small amount of an optically active isocyanate, 4 -6 and for the polymers obtained with an optically active anionic initiator. 7 Poly(alkyl isocyanate)s are also known to exist in a predominantly one-handed helical conformation in optically active solvents. 8 • 9 On the other hand, poly(aryl isocyanate)s had been considered to have a random coil conformation due to the lack of stiffness in the main chain compared with poly(alkyl isocyanate)s. However, we recently found that achiral aryl isocyanates also can afford optically active polymers in the polymerization with chiral anionic initiators.10 This indicates that poly(aryl isocyanate)s as well as poly(alkyl isocyanate )s are able to have a helical structure in solution. We also reported that the helix reversal of poly(m-methylphenyl isocyanate) (poly-(mMePI)) with a chiral group at the IX-end begins to occur at DP= I 3 through the chiroptical study on the oligomers.11 However, much less study on the helical structure of poly(aryl isocyanate)s ...

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Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 91%

Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Maeda

1998

Polym J

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“…Figure 9 shows a comparison between experiment and theory for chirally initiated poly(m-methylphenyl isocyanate) (PmMePI/Li-MMP). 27 In the panel (a), theoretical curves for different v values are drawn to approximately follow the data points by choosing appropriate values for [aJm(a-1)/(a+ 1). The data for N larger than 13 can be fitted accurately to the theory In the above treatment, [ocJm is defined as the specific rotation of monomer residue in a perfect helical conformation and is assumed not to depend on chain length.…”

Section: Analysis Of Experimental Datamentioning

confidence: 99%

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Sato

Teŕamoto

et al. 1997

Polym J

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ABSTRACT:Molecular mechanisms were proposed to account for extraordinary optical activities of polyisocyanates containing chiral moieties (chiral monomer or initiator fragment) reported by Green et al. and by Okamoto et al., where the polyisocyanate molecule was modeled by a helical chain consisting of an alternating sequence of right-handed and left-handed helices with helix reversals in between. Theoretical predictions based on this model were consistent with remarkable dependence of optical rotation on monomer composition for random copolyisocyanates of chiral and achiral monomers and enantiomorphous copolymers and chain length dependence of optical rotation for achiral polyisocyanates with a chiral initiator fragment on the chain end. The helix reversal was shown to be the key factor for all the cases and more frequent for aromatic sidechain polymer poly(m-methyl phenyl isocyanate) than for aliphatic side chain polymers such as poly(butyl and hexyl isocyanate)s.KEY WORDS Chiral / Optical Activity / Polyisocyanate / Helical Conformation / Helix Reversal / Statistical Mechanics / Copolymer / Amide bonds of partial double-bond nature in a polyisocyanate chain tend to be coplanar, but they are distorted in a helical conformation due to steric interactions between the main chain and side chains. 1 -1° For this reason the global conformation of the polymer chain is well modeled by wormlike chains. 7 -9 • 11 -18 However the sense of the helix is not determined for an achiral polyisocyanate because both the right-handed and lefthanded helices are symmetric. This symmetry is broken by a subtle chiral perturbation within a given molecule and this molecule becomes optical active. [19][20][21][22][23][24][25] showed that incorporation of a very small amount of chiral monomers into an achiral polyisocyanate in a random fashion gives rise to remarkable optical activity, which increases disproportionately with the mole fraction of chiral monomer. A similar disproportionate change in optical activity has been found in copolymers of enantiomorphous isocyanates (R-S copolymers). 25 On the other hand Okamoto and collaborators 26 • 27 introduced a chiral perturbation into polyisocyanate chains in a different way; they synthesized polyisocyanates with chiral initiators, which were attached to a chain end, and showed that those polyisocyanates exhibited optical activity changing remarkably with length and temperature. The present study was motivated by these findings and tries to explore the molecular mechanisms behind the optical activities in these particular polymers. Green et al. 20 called chiral entities sergeants and achiral entities soldiers. Thus we here deal with sergeants-soldiers polymers. Theoretically these polyisocyanates are regarded as typical linear cooperative systems just as chiral polyisocyanates and a-helical polypeptides. Therefore we analyze their conformational properties including optical activity by the well-established statistical mechanical procedures based on the matrix method. 28 -30 A preliminary...

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“…The CD intensity of 2 depended on the molecular weight, and the polymer prepared in run 2 exhibited the largest intensity. Previously, Okamoto and coworkers52–55 reported similar observations for polymers prepared by the asymmetric polymerization of phenylisocyanate derivatives; they clarified that the persistence length of the helical structure was relatively short for the poly(phenyl isocyanate) bearing the chiral initiator residue in the terminal end and that the one‐handed helical sequences decreased with an increasing degree of polymerization. Therefore, polymer 2 should partially form a one‐handed helical structure, which was preserved by the chirality of MMP bonding to the terminal end in 2 .…”

Section: Resultsmentioning

confidence: 60%

“…The asymmetric polymerization using a chiral initiating system is extensively known as an effective approach to producing a one‐handed helical polymer, and this strategy has been applied to the preparations of a number of helical polymers 42–51. In fact, Okamoto and coworkers52–55 achieved the synthesis of a one‐handed helical polyisocyanate by means of this synthetic procedure. Thus, the asymmetric polymerization of phenylisocyanate bearing crown ether should be a suitable candidate for producing the one‐handed helical arrays of crown ether.…”

Section: Introductionmentioning

confidence: 99%

Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

Sakai

Otsuka

Satoh

et al. 2005

J. Polym. Sci. A Polym. Chem.

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The asymmetric polymerization of 4′‐isocyanatobenzo‐18‐crown‐6 with the lithium amide of (S)‐(2‐methoxymethyl)pyrrolidine successfully proceeded to afford end‐functionalized poly(4′‐isocyanatobenzo‐18‐crown‐6) with (S)‐(2‐methoxymethyl)pyrrolidine (polymer 2). In the circular dichroism (CD) spectrum of 2, a clear positive Cotton effect was observed in the range of 240–350 nm corresponding to the absorption of the polymer backbone, indicating that 2 partially formed a one‐handed helical structure, which was preserved by the chirality of (S)‐(2‐methoxymethyl)pyrrolidine bonding to the terminal end in 2. In the titration experiments for the CD intensity of 2 in the presence of D‐ and L‐Phe·HClO4 (where Phe is phenylalanine), a small but remarkable difference was observed in the amount of the chiral guest needed for saturation of the CD intensity and in the saturated CD intensity, indicating that the extremely stable, one‐handed helical part should exist in the main chain of 2, which was not inverted even when the unfavorable chiral guest for the predominant helical sense, L‐Phe·HClO4, was added. In addition, helical polymer 2 exhibited a chiral discrimination ability toward racemic guests; that is, the guests were extracted from the aqueous phase into the organic phase with enantiomeric excess. The driving force of the chiral discrimination ability of 2 should certainly be attributed to the one‐handed helical structure in 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 325–334, 2006

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Chiroptical Properties of Oligomers of m-Methylphenyl Isocyanate Bearing an Optically Active End-Group

Cited by 44 publications

References 10 publications

Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Helical Structure of Oligo- and Poly(m-substituted phenyl isocyanate)s Bearing an Optically Active End-Group

Molecular Mechanisms for the Optical Activities of Polyisocyanates Induced by Intramolecular Chiral Perturbations

Chiral discrimination of a helically organized crown ether array parallel to the helix axis of polyisocyanate

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