Electric Dichroism and Polymer Conformation. II. Theory of Electric Dichroism, and Measurements on Poly(n-butyl isocyanate)

Troxell, Terry C.; Scheraga, Harold A.

doi:10.1021/ma60023a002

Cited by 68 publications

(42 citation statements)

References 10 publications

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“…For this polymer we have one unit (i= 1) with uM,l > Up, i( = 1 /uM, 1) and the other unit (i = 2) with uM, 2 = up, 2 = 1 for sergeant-soldier copolymers and uM, 2 = 1/uM,l and Up,2 = 1/up,1 for enantiomorphous copolymers and for simplicity we assign the same small value v(«l) to v of both units (v1 =v 2 (9) where < ) means the average of a given quantity over polymer species with random sequence in the given sample. It is easy to extend this treatment to polymers consisting of two or more types of chiral units.…”

Section: Type 1 Polymersmentioning

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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Section: Type 1 Polymersmentioning

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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“…Despite these extensive studies, however, the conformation and molecular packing of PAICs have yet to be unequivocally established. For example, several helical conformations have been proposed, namely 2 1 , 5 1 and 8 3 in solution [9][10][11][12] and 8 3 , 8 5 and 12 5 in the solid state. [13][14][15] Furthermore, triclinic, monoclinic and pseudo-hexagonal lattices have all been proposed as possible molecular packing structures.…”

Section: Introductionmentioning

confidence: 99%

Reversible conformation-driven order–order transition of peptide-mimic poly(n-alkyl isocyanate) in thin films via selective solvent-annealing

et al. 2012

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We report for the first time the conformational and structural details of peptide-mimic poly(n-hexyl isocyanate) (PHIC). PHIC is a representative poly(n-alkyl isocyanate)s, which have received significant attention because of their unique stiff chain characteristics and potential applications in various fields. A well-ordered hexagonal close packing structure of PHIC with 8 3 helical conformation was clearly observed in the nanoscale thin films that were selectively annealed with carbon disulfide (CS 2 ). A well-ordered multi-bilayer structure of the polymer with b-sheet conformation was also clearly formed in the films that were selectively annealed with toluene. In addition, a fully reversible transformation between these two self-assembled structures was demonstrated by consecutive annealings with CS 2 and toluene.

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“…3 LD can be used to probe the orientation of chain constituents in polymers. 4,5 Hence, measurements of LB and/or LD can lead us to an important understanding of polymer structure and properties. Deshpande 6 has demonstrated a near-infrared spectropolarimeter ͑NIRSP͒ as a new measurement technique for inline polymer process monitoring and feedback, which can lead to better process feedback control algorithms for reduction of manufacturing variation in rheological properties and energy consumption.…”

Section: Introductionmentioning

confidence: 99%

Near-infrared spectropolarimeter using an acousto-optic tunable filter

et al. 2007

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The long chain of a polymer molecule often has intrinsic linear birefringence and/or dichroism, which lead to macroscopic properties when the molecules have a preferred orientation under nonequilibrium conditions, such as flow of a polymer melt. Measurements of properties, including linear birefringence, in a polymer melt can in turn lead to valuable insights into its structure, morphology, and rheology. We demonstrate that a spectropolarimeter based on an acousto-optic tunable filter can measure linear birefringence in real time during the manufacture of polymers, at hundreds of wavelengths, within 5 min, and thus provides more information than use of a spectrometer or laser-based polarimetry alone. In this work, optical properties of different molten ethylene vinyl acetate samples were measured with a spectropolarimeter based on an acousto-optic tunable filter and a photoelastic modulator in the near infrared. Regression models of the results indicate good correlation between the melt indices of the samples and the measured spectra.

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Electric Dichroism and Polymer Conformation. II. Theory of Electric Dichroism, and Measurements on Poly(n-butyl isocyanate)

Cited by 68 publications

References 10 publications

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

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

Reversible conformation-driven order–order transition of peptide-mimic poly(n-alkyl isocyanate) in thin films via selective solvent-annealing

Near-infrared spectropolarimeter using an acousto-optic tunable filter

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