Rigid-rod Structure Research Articles

Structure−Activity Relationship of New Nonlinear Optical Organic Materials Based on Push−Pull Azo Dyes. 3. Guest−Host Systems

Several new push−pull azobenzene dyes with different electron-withdrawing groups, steric hindrance, and hydrogen-bonding capabilities were dispersed in poly(N-methacryloyl-N‘-phenylpiperazine), a glassy polymer matrix. After orientation by corona poling, the second harmonic generation (SHG) signals of the guest−host systems were measured as a function of time and temperature and fitted with Kohlrausch−Williams−Watts (KWW) stretched exponentials. The variations of their nonlinear susceptibilities at time zero and in their relaxation behavior were correlated with the changes of the chromophore chemical structure. Rigid rod structures always presented the best orientability and stability of the nonlinear optical properties.

Experimental studies of the deformation of soil beds reinforced with rod elements

A procedure for and results of experimental investigation of the effect of the reinforcement of a soil bed by rigid rod structures on its deformation properties are cited. A conclusion is drawn concerning the strengthening of a soil where the ratio of the area of reinforcing elements to the loaded surface is 1:80 and higher. It is demonstrated that the reinforcement of soil is associated primarily with the constraint of plastic deformations and does not affect the properties of the soil mass being deformed.

Aggregation kinetics and precipitation phenomena in poly(phenylisocyanide)

The preparation of N-phenyl-substituted poly(isocyanide) (N-ϕ-PIM) utilizing a Ni(II) catalyst in methanol yields a brown material having a number average molecular weight of about 2000. Analysis of this “as prepared” polymer indicates that a rigid rod structure is present in the derived solid. Dissolution of this “as prepared” N-ϕ-PIM in halocarbon solvents or THF apparently leads to unraveling of the helical polymer with subsequent aggregation and precipitation of materials that have different properties from the original. These processes have been investigated by NMR, GPC, and light-scattering techniques in THF and other solvents. UV spectroscopy has been utilized to follow the kinetics of the aggregation process in solution. X-ray diffraction (XRD) measurements have been employed to investigate the changes attendant with precipitation. An explanation of these observations is offered that implicates the uncoiling of the rigid rod helix as the most important step in defining subsequent physical and chemical properties of the ultimate amorphous polymer. © 1997 John Wiley & Sons, Inc.

側鎖にバルキーな置換基を有する芳香族コポリエステルの結晶化における活性化エネルギー

The activation energy for the crystallization of an aromatic copolyester with bulky side group was obtained by using a differential scanning calorimeter (DSC). The results of non-isothermal crystallization experiments indicate that there are two crystallization processes; the fast process and the slow process. The crystallization during cooling is controlled by diffusion. The activation energy for the slow process is quite large because of difficulty in diffusion of a molecule due to the rigid rod structure. On the other hand, the isothermal crystallization takes place by nucleation and growth. The activation energy based on kinetic data was 645kJ·mol-1. The value is somewhat larger than those of flexible polymers because of the large energy barrier in molecular movement due to the rigid backbone and bulky side groups. The equilibrium melting temperature and heat of fusion were determined, and the equilibrium entropy change of 0.63J·mol-1·K-1 was calculated from the thermodynamical relationship, ΔSf°=ΔHf°/Tm°. Compared to the literature values for flexible polymers such as polyethylene (9.88J·mol-1·K-1) and polypropylene (15.1J·mol-1·K-1), the obtained value is rather small. This is because the transition from nematic melt to crystals induces less entropy change than that from isotropic melt to crystals.

Hydrophilic poly-ylids derived from 4,4′-bipyridyl: synthesis, structure and membrane-forming characteristics

Interfacial polycondensation of 1,1′-diamino-4,4′-bipyridinium di-iodide, [H 2 N- + NC 5 H 4 -C 5 H 4 N + -NH 2 ]I 2 , with aromatic di- or tri-acyl chlorides, affords a novel class of hydrophilic polymers. These materials are isoelectronic with polyesters but contain ylid linkages [N − -N − -CO] in place of ester bonds [C-O-CO]. Non-crosslinked polymers of this type are insoluble in conventional organic solvents but dissolve readily in proton-donor solvents such as formic and trifluoroacetic acids. Single-crystal X-ray studies of the model oligomer C 6 H 5 CO-N − - + NC 5 H 4 -C 5 H 4 N + -N − -COC 6 H 5 reveal an essentially rigid-rod structure and, in keeping with this, the poly-ylids derived from terephthaloyl chloride and naphthalene-2,6-diacyl chloride exhibit lyotropic liquid crystallinity. Interfacial syntheses of poly-ylids on ultrafiltration membranes afford supported membranes with nodular morphology and useful nanofiltration properties.

Ultimate Properties of Polymer Chains

AbstractNew polymers with exceptional properties are needed for applications in high-performance structures, novel electrical, optical and electro-optical devices, and for multi-functional smart materials. Concurrently, new computational capabilities and methods for properties prediction and analysis have enabled the study of a variety of polymer chain architectures to examine the principles that govern their high-performance properties. By semi-empirical and ab initio computational methods, flexible, stiff-chain, rigid-rod, and biological structures could be analyzed. Single chain molecular stress-strain curves for axial tension and compression were calculated, and the strain dependence of the molecular modulus and vibrational frequencies were compared to measurements of molecular deformation, such as IR and Raman spectroscopy. However, of special interest is the distinctly different response of alpha-helical biopolymer chains to strain. Indeed, in this study we compare on a theoretical basis the ‘spring-like’ microscopic mechanical response of alpha-helical biopolymers having a reinforcing intra-molecular hydrogen bonding network to analogous synthetic extended chain polymers, especially poly(para-phenylene terephthalamide) (PPTA) [KEVLARTM]. The theoretical verification of the absence of compressive buckling in alpha-helical biopolymer chains rationalizes the molecular elasticity and resistance to ‘kinking’ of those strands, manifested by the prevalence in Nature for coiled coils. The understanding of the structure-tofunction relationship in biopolymers explaining the role of the alpha-helix in these systems as a requirement for superior compressive mechanical properties, may enable new guidance for the synthesis of motifs consistent with molecular frameworks optimized by Nature.

Design and architecture of macromolecular structures

AbstractMacromolecules exist in a variety of molecular and super‐molecular arrangements. Among these are random coils and regular polymer structures with extended chain, some with lamellar and spherulitic morphology and rigid rod structures. An important macromolecular arrangement is the helical structure. For the control of the synthesis of the perfect helix, the stereochemistry of the oligomerization was studied; the best example for this investigation was found to be the oligomerization of the trihaloacetaldehydes, e.g. fluoral, chloral and bromal.

Thermotropic liquid‐crystalline polyesters and polyesteramides

AbstractThermotropic behaviour is observed in a number of aromatic polyesteramides containing p‐phenylene or substituted p‐phenylene groups. In such polymers, a substantial proportion of co‐polymerised units lacking rigid rod structure can be tolerated without loss of thermotropic behaviour. Anisotropic melts can be formed at very short average chain length. The upper temperature limit of stability of the anisotropic phase is lower the shorter the average chain length and the greater the proportion of relatively flexible units. Some polyesteramides formally derived from p‐N‐methylaminophenol also exhibit thermotropic behaviour.

Mechanism of bovine liver glutamate dehydrogenase self-assembly. III. Characterization of the association-dissociation stoichiometry with quasi-elastic light scattering.

Abstract The homodyne light-scattering autocorrelation function originating in translational diffusion has been simulated for a polymerization model proposed for a number of self-associating systems: the sequential addition of identical monomer units to a growing aggregate, with identical equilibrium constants for each step. Both spherical and rigid rod structures have been considered. When applied to quasi-elastic light scattering data on glutamate dehydrogenase self-assembly, the simulation results indicate the formation of elongated polymers having equivalent and identical association sites. The weak response of translational diffusion coefficients to solution non-ideality leads to a valuable test of the unique equilibrium constant assumption. On the other hand, it is shown that successful exploitation of quasi-elastic light scattering data on aggregating systems of this type relies heavily on independent information.

Remarks on polyelectrolyte conformation

We discuss the conformations of linear polyions assuming that a) the corresponding uncharged chain is flexible ; b) electrostatic forces dominate the monomer-monomer interactions; c) no salt is added. 1) For the dilute case (non overlapping chains) correcting a recent self-consistent calculation by Richmond [1a], we find an overall polyion size R = Nd which is a linear function of the polymerization index N in agreement with the early work of Hermans and Overbeek, [1b], Kuhn, Kunzle, and Katchalsky [1c]. 2) There is a range of very low concentration c (c** c**) : here we expect that the polyions build up a 3-dimensional periodic lattice ; however, the detection of such an extremely dilute lattice appears difficult. 3) Practically all experiments on salt-free polyelectrolytes have been performed at concentrations c > c* where different chains overlap each other. To discuss this regime we restrict our attention to cases where the charge per unit length is near (or above) the condensation threshold : then a single length ξ( c) characterizes the correlation; in 3 dimensions ξ scales like the Debye radius associated with the counter ions. We consider several possible conformations : a) hexagonal lattice of rigid rods ; b) cubic lattice of rigid rods ; c) isotropic phase of partially flexible chains. The various rigid rod structures appear to have very similar electrostatic energies. This suggests that the isotropic phase might possibly be the most favorable. We analyse this latter phase using the same scaling methods which have recently been helpful for neutral polymer solutions (2). In the isotropic model each chain behaves like a succession of segments of size. Inside one segment electrostatic effects are important and similar to case (1) above. Between segments the interactions are screened out, and tach chain is ideal on a large scale, with radius R (c) ∼ c-1/4 N1/2 . If we (tentatively) assume that the dynamical effects of entanglements are weak, we are than led to a viscosity ηsp/c ∼ Nc-1/2.