Fiber macromolecules, structure

Hoogsteen, W, Postema, A.R., Pennings, A.J., and ten Brinke, G. (1990) Crystal structure, conformation, and morphology of solution-spun poly(L-lactide) fibers. Macromolecules, 23, 634-42. 

Kaba, V, Kakad, P.A., Mendez, S. etal. (2006) Self-assembled structures in electrospun poly(styrene-block-isoprene) fibers. Macromolecules, 39,5453-5457. 

Liquid crystalline structures are not limited to compounds with low molecular weight. A curious example of liquid crystalline macromolecule is the silk fibroin, which is naturally produced by silkworm. This protein fiber exhibits liquid crystalline order in the liquid silk flowing out from the silk gland [4], Macromolecule structures with liquid crystalline properties are particularly appealing to the... 

Contrary to widespread opinion, the value of Ea is not a constant quantity. As was proved previously [52], the value of E is variable, since it depends on the ordering of macromolecules in the amorphous material of the fiber. At the same time, one can suppose that this ordering will be affected by the specificity of the fine structure of the fiber, and particularly by the type of substructure of the fiber. The relationship determining the modulus Ea appropriate for a definite type of fiber substructure can be derived from Eq. (11) when appropriate values of A are assumed. In the case of the microfibrillar substructure, i.e., for A < I, typical of PET fibers stretched, but not subjected to annealing, this equation has the form [52] ... 

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

The mechanism of carcinogenesis by PAHs is believed to involve alkylation of an informational macromolecule in a critical, but at present unknown, manner. Such an interaction with a protein has been modelled by alkylation of a peptide this showed a conformational change occurred on alkylation. It has not yet been possible to study the structure of DNA alkylated by an activated carcinogen this is because DNA is a fiber and the structural order in it is not sufficient for a crystal structure determination. However the crystal structures of some alkylated portions of nucleic acids are described, particularly some nucleosides alkylated by chloromethyl derivatives of DMBA. In crystals of these alkylation products the PAH portion of the adduct shows a tendency to lie between the bases of other nucleoside... 

In the laboratories of Natta in Milan it was found that the Ziegler catalysts could polymerize (besides ethene) propene, styrene, and several a-olefins to high linear polymers. These polymers appeared crystalline when examined by X-ray diffraction techniques and were able to give oriented fibers. In less than one year since the preparation of the first polymer of propene, Natta was able to communicate, in the meeting of the Accademia dei Lincei of December 1954 in Rome, that a new chapter had been disclosed in the field of macromolecular chemistry, due to the discovery of processes to obtain polymers with an extraordinary regularity in their structure in terms of both chemical constitution and configuration of the successive monomeric units along the chain of each macromolecule. 

In 1926 Staudinger was totally involved in defending his ideas regarding the macromolecule. On the other hand, Mark, at the Fiber Research Institute in Dahlem, was riding the crest of acclaim as an outstanding crystallographer and expert in molecular structure. The two were requested to present papers by R. Willstaetter at a special symposium of the "Gesellschaft Deutscher Naturforscher und Arzte". 

In 1923 one of Mark s superiors handed him a piece of hemp and asked that he study its molecular structure. Hemp was one of the many natural materials we now recognize as macromolecules which to then defied structural analysis. After much thought and work, also including X-ray studies, he concluded that the hemp fiber contained crystals. On examination, so also did cotton, wood and flax. 

The latest results of a controlled crystallization of macromolecules are the polymer fibrids which are a completely new modification of synthetic polymers as far as the micro- and macro-structure is concerned. They exist of small fibers having a length of up to some millimeters, which are highly oriented, and which have a macro-morphology similar to that of cellulose pulp. 

Lignin in the true middle lamella of wood is a random three-dimensional network polymer comprised of phenylpropane monomers linked together in different ways. Lignin in the secondary wall is a nonrandom two-dimensional network polymer. The chemical structure of the monomers and linkages which constitute these networks differ in different morphological regions (middle lamella vs. secondary wall), different types of cell (vessels vs. fibers), and different types of wood (softwoods vs. hardwoods). When wood is delignified, the properties of the macromolecules made soluble reflect the properties of the network from which they are derived. 

Just as the amino acids, sugars, and nucleotides are the building blocks for formation of proteins, polysaccharides, and nucleic acids, these three kinds of macromolecule are the units from which larger subcellular structures are assembled. Fibers, microtubules, virus "coats," and small symmetric groups of subunits in oligomeric proteins all result from the packing of macromolecules in well-defined ways, something that is often called quaternary structure. 

This accounts for the substantially higher effectiveness compared to the fibers as a consequence of their microscopic dimensions, the macromolecules are able to engage in the production and growth stages of eddies considerably earlier, thus exerting a sustained damping influence on the axial and radial turbulence structure, as conformed by LDA measurements in injection experiments. 

The same geometric and mathematical principles lie at the root of all types of diffraction experiments, whether the samples are powders, solutions, fibers, or crystals, and whether the experiments involve electromagnetic radiation (X rays, visible light) or subatomic particles (electrons, neutrons). My aim in this chapter was to show the common ground shared by all of these probes of molecular structure. Note in particular how the methods complement each other and can be used in conjunction with each other to produce more inclusive models of macromolecules. For example, phases from X-ray work can serve as starting phase estimates for neutron work, and the resulting accurate... 

An important parameter influencing the mode of action of cellulases is the accessibility of the cellulose to the enzymes. The molecular weights of cellulases range between 30 and 80 kDa. A comparison of the size of cellulase (3-8 nm) and the pore size of cotton swollen in water (1-7 nm) shows very clearly that cellulases can penetrate the cellulose to a limited extent only. In addition, the enzyme reaction takes place preferentially on amorphous cellulose because the more compact, crystalline cellulose structures do not offer any space for such macromolecules. Thus - provided of enzyme and process parameters have been selected correctly -cellulases act mainly on the textile surface. In this way interesting effects on cellu-losic fibers can be achieved. 

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