Crystalline polymerization

PET fibers in final form are semi-crystalline polymeric objects of an axial orientation of structural elements, characterized by the rotational symmetry of their location in relation to the geometrical axis of the fiber. The semi-crystalline character manifests itself in the occurrence of three qualitatively different polymeric phases crystalline phase, intermediate phase (the so-called mes-ophase), and amorphous phase. When considering the fine structure, attention should be paid to its three fundamental aspects morphological structure, in other words, super- or suprastructure microstructure and preferred orientation. 

The strengths of polymers in the glassy state exceed those of amorphous polymers at temperatures above Tg, but they are generally much inferior to the strengths attainable in oriented crystalline polymeric substances. 

Interest in understanding the details of the crystalline structure arises from the fact that crystallinity controls the properties of semi-crystalline polymeric materials. The characterization of each of the phases of the structure has long... 

Activity in the field was, however, expanding. For example, in 1927 Drew and Haworth (65) obtaind a crystalline polymeric powder by the action of hydrogen chloride on the lactone of 2,3,4-trimethyl-l-arabonic acid. Citing the increase in melting point and molecular weight, and loss of specific optical rotation, they ascribed a cyclic, high polymer structure to this polyester. 

Morphology is the order or arrangement of the polymer structure. The possible order between a molecule or molecule segment and its neighbors can vary from a very ordered highly crystalline polymeric structure to an amorphous structure (i.e., a structure in greatest disorder or random). The possible range of order and disorder is clearly depicted on the left side of Fig. 1.14. For example, a purely amorphous polymer is formed only by the non-... 

Special attention should be paid to rheological behavior of liquid crystalline polymeric systems, which although being similar to that of low-molecular liquid crystals, still has some peculiarities. Without going into a detailed discussion of rheological properties, which are described in separate articles and reviews we shall mention some of their features. 

One more distinguishing feature of liquid crystalline polymeric systems is a peculiar dependence of the viscosity on the shear stress (r) when the latter is small. Kulichikhin et al. were the first to note that in the range of small shear stresses the... 

We shall mention here another property of liquid crystalline polymeric systems. As in the case of low-molar mass liquid crystals, when electric and magnetic fields are applied, liquid crstalline domains get oriented along the direction of the field. Rearrangement of a polymer structure under the effect of a magnetic field was demonstrated in for a PBA-dimethylacetamide system. However, the processes of... 

The design and synthesis of new liquid crystalline polymeric materials endowed with intrinsc chirality deserve attention, as chirality can offer probes of the supermolecular structure and a tool for modulating specific responses of the polymers (1). The chemical transformation of preformed thermotropic polymers can add novel opportunities for the realization of various molecular architectures conventionally unfeasible and best suited for mesophase modification. 

When Interpreting spectra such as these. It Is Important to remember that we are not dealing with a nearly lOOX crystalline material (as are most conventional dlacetylene monomers), but rather, a relatively poorly ordered semi-crystalline polymeric material (approximately lOX crystalline as solution cast). This means that there will be amorphous regions, some crystalline regions which will have varying degrees of defect density, and some nearly perfectly ordered crystalline regions. 

Fig. 10. Schematic illustration of supramolecular liquid-crystalline polymeric complexes I side-chain type II main-chain type III combined type and IV network type...

X-ray diffraction techniques are the only way of determining the crystal structure of natural and synthetic polymers, although the x-ray data itself obtained from a crystalline polymeric fiber or film is not sufficient to allow complete refinement of the structure. Conformational analysis and electron diffraction represent complementary methods which will facilitate the determination of the structure. The necessary requirements for the x-ray approach are crystallinity and orientation. X-ray data cannot be Obtained from an amorphous sample which means that a noncrystalline polymeric material must be treated in order to induce or improve crystallinity. Some polymers, such as cellulose andchitin, are crystalline and oriented in the native state.(1 )... 

This concept has been extended to melting in crystalline polymeric systems. We must remember, however, that in the case of crystalline polymers ... 

M. K. Bisaria, P. Andrin, M. Abdou, and Y. Cai. Injection moldable conductive aromatic thermoplastic liquid crystalline polymeric compositions. US Patent 6 379 795, assigned to E. 1. du Pont de Nemours and Company (Wilmington, DE), April 30, 2002. 

The possibility of converting light into mechanical energy has been impressively demonstrated with cross-linked liquid-crystalline polymeric systems containing azobenzene groups that were prepared by polymerizing previously aligned mixtures of acrylate 1-AC and diacrylate 2-AC (see Chart 5.10) [51]. 

Ao. (J = f/Aq. This is called engineering stress, it is easier to measure in practice, because to determine the true stress f/A, one needs to measure both f and A. Stress has dimension of pressure and here it is presented in the units of megaPascal (a useful reminder for the book on molecules 1 MPa= 1- ). Strain is presented as unitless relative elongation of the sample A f o. Panel (a) presents data for an isotropic semi-crystalline polymeric material, specifically — low density polyethylene film. The inset presents a wider interval of strains. Notice that at low... 

In the end, one obtains some truly fantastic materials. For instance, the airbags which allow for soft landing of spacecraft on Mars are made of liquid crystalline polymeric fiber called vectran. This must be a truly special material ... 

Thermodynamics, both classical [Appendix 3.A] and statistical [Appendix 2A], have been applied to many topics in polymer science. The results have provided insights into the origin of rubber elasticity, the nature of polymer crystalline, polymeric heat capacities and the miscibility of polyblends. 

Methacrylonitrile polymerizes readily in inert solvents. The polymer, depending on the initiator and on reaction conditions, is either amorphous or crystalline. Polymerizations take place over a broad range of temperatures from ambient to -5 °C, when initiated by Grignard reagents, triphenyl-methylsodium, or sodium in liquid ammonia. The properties of these polymers are essentially the same as those of the polymers formed by a free-radical mechanism. 

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