Rigid Backbone Polymers. 4. Solution Properties of Two Lyotropic Mesomorphic Poly(isocyanates)

Aharoni, Shaul M.; Walsh, Eugene K.

doi:10.1021/ma60068a021

Cited by 100 publications

(42 citation statements)

References 5 publications

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“…It should be noted that the extension of the anisotropic domains is only a few tens of microns, even after 6 weeks. In addition, it was observed that, as previously reported [6], the application of a normal stress to the top of the cover glass plate induces characteristic patterns with elongated domains which relax within a few days.…”

Section: Microscopysupporting

confidence: 77%

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Mesophase formation in high molecular-weight xanthan solutions

1988

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After a short review of theoretical background on mesophase formation in polymer solutions, this paper describes the liquid crystal phase transition and the corresponding rheological properties for aqueous solutions of a high-molecularweight xanthan sample (M w g 1.8.106). The formation of mesophases has been studied using polarizing microscopy and viscometry. The effects of the presence of salts, bacteria cells and proteins have been investigated. The variations in the viscosity, due to mesophase formation, are in qualitative agreement with the predictions of Matheson's theory, but the onset of the ordered phase occurs at very low polymer concentrations and the diphasic domain is much broader than predicted by thermodynamic models. These characteristics of the phase transition are related to the very high molecular weight of the sample studied and can be explained mainly by the effects of cooperative interactions between xanthan chains and of chain flexibility reducing translational entropy.

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Section: Microscopysupporting

confidence: 77%

“…These mesophases have been observed, by using cross-polarized light microscopy and viscometry, in various macromolecular systems e.g. aromatic polyamides [1][2][3][4], polyisocyanates [5,6], cellulosic polymers [7][8][9][10][11][12] and, more especially, polysaccharides [13 151.…”

Section: Introductionmentioning

confidence: 99%

Mesophase formation in high molecular-weight xanthan solutions

1988

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“…(z,)""p1*) (8) Under the assumption that the orientation distribution for rigid sequences depends only on their length 7, we let…”

Section: Derivation Of the Configuration Partition Functionmentioning

confidence: 99%

“…In particular, the predicted minimum solute concentration necessary for the separation of a stable anisotropic phase in exothermal and in nearly athermal mixtures is in good accord with experiments on poly(y-benzyl L-glutamate) in n -c r e~o l~~~ and in dimethylformamide,6 on poly@-benzamide) in N,N-dimethyla~etarnide,~ and on poly(hexy1 isocyanate) in tetrachloroethane. 8 In fact, theory and experiment may be in better agreement than was frst indicated, when the onset of phase separation was identified erroneously with the sharp drop in viscosity that occurs upon increasing the solute concentration. Recent s t u d i e~~~~~~ demonstrate that incipient phase separation occurs at a lower concentration than that at which the viscosity is observed to decrease.…”

Section: Introductionmentioning

confidence: 99%

Statistical thermodynamics of mixtures of semirigid macromolecules: chains with rodlike sequences at fixed locations

Matheson¹,

Flory²

1981

Macromolecules

157

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Semirigid macromolecules consisting of one or more rigid, rodlike sequences of units in combination with flexible (random coil) units are treated according to the adaptation of the lattice model to a system of rods. The lengths and locations of the rigid sequences within each macromolecule are considered to be fixed by its structure. They are separated by various specified numbers of random coiled units. Polydispersity is taken into account. General expressions are derived for the chemical potentials, and biphasic equilibria between nematic and isotropic phases are investigated. The presence of a very few random coiled units increases the disorder in the anisotropic phase, narrows the biphasic gap, and suppresses fractionation of species differing in length in polydisperse systems. The introduction of internal points of flexure, even in absence of intervening random units, produces similar effects to a degree that depends markedly on the locations of the points of flexure.

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“…Lyotropic mesophases of polypeptides, 1-10 polyisocyanides, [11][12][13][14] and polyisocyanates [15][16][17][18][19][20][21][22] have been identified and reported. During our efforts to develop new helical materials, we found that carbodiimides can be polymerized in a living fashion using a variety of transition metal complexes.…”

Section: Introductionmentioning

confidence: 99%

Liquid Crystalline Properties of Polyguanidines

2004

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Modified polyguanidines were prepared, and their liquid crystalline properties were studied using optical polarizing microscopy and X-ray diffraction. Parameters examined include chirality, the uniformity of the lengths of side chains, and attached side-chain mesogens. If the side chains on the repeat units are identical, then polymer has a more ordered structure in both solution and the solid state. Uniform lengths of the side chains are also important. Poly(N,N′-di-n-hexylguanidine), poly-I, exhibited a lyotropic smectic texture in contrast to a nematic texture of poly(N-(rac)-2-phenylethyl)-N′-methylguanidine) (poly-(rac-II)). Optically pure poly(N-((R)-2-phenylethyl)-N′-methylguanidine) (poly-(R-II)) formed a cholesteric texture, whereas the corresponding racemic polyguanidine, poly-(rac-II), formed a nematic texture. Additionally, poly-(R-II) displayed a mesophase at a lower critical concentration than either poly-I or poly-(rac-II), implying that poly-(R-II) is stiffer than these two other derivatives. Poly(N-6-((4′-methoxyphenylazo)phenyl-4-oxy)hexyl-N′-n-hexylguanidine) (poly-IV), one of combined liquid crystalline structures (liquid crystalline backbone plus liquid crystalline side chains), displayed a lyotropic nematic texture presumably due to the strong dipolar-dipolar interaction between the main chain and side chains that folds the appendages parallel to the molecular axis. Poly(N-12-((4′-methoxybiphenyl-4-oxy)dodecyl-N′-n-dodecylguanidine) (poly-V) and poly(N,N′-di-n-dodecylguanidine) (poly-VI) exhibited thermotropic liquid crystalline behavior.

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Rigid Backbone Polymers. 4. Solution Properties of Two Lyotropic Mesomorphic Poly(isocyanates)

Cited by 100 publications

References 5 publications

Mesophase formation in high molecular-weight xanthan solutions

Mesophase formation in high molecular-weight xanthan solutions

Statistical thermodynamics of mixtures of semirigid macromolecules: chains with rodlike sequences at fixed locations

Liquid Crystalline Properties of Polyguanidines

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