Oriented polymers structure

The absence from a formula of any one of the horizontal or vertical lines at a chiral or prochiral carbon atom (as in examples on pages 27 and 32), or of or Z designations at double bonds, indicates that the configuration of that stereoisomeric centre is not known. Also, as in our previous document [2], the convention of orienting polymer structures (and the corresponding constitutional and configurational units) from left to right is used. Thus, the two bracketted constitutional units in... 

Numerous monomers were irradiated, and it was shown that either free radical or ionic polymerizations would take place depending on experimental parameters. Several monomers were found to undergo a chain polymerization when irradiated in the crystalline state. This unexpected behavior led to a revision of basic concepts regarding reactivities in solids. Some interesting oriented polymer structures were formed in certain cases (see ref. 15). 

The interference bands on the fracture surfaces, which relate to the craze at the crack tip, were first observed by Berry [31] and by Higuchi [32]. Kambour confirmed that the PMMA fracture-surface layers were qualitatively similar to the internal crazes of this polymer, by showing that the refractive indices were the same [15]. Both surface layer and bulk crazes appear to be oriented polymer structures of low density, which are produced by orienting the polymer under conditions of abnormal constraint it is not allowed to contract in the lateral direction, while being extended locally to strains of the order of unity, and so has undergone inhomogeneous cold-drawing. 

A. Peterlin, Molecular Aspects of Oriented Polymers - Structure and Properties of Oriented Polymers, Ed. by I. M. Ward, Appl. 

Oriented polymer structures are extremely important as commercial materials since they allow the high unidirectional strength of the polymer molecules to be exploited. 

FIGURE 33.9 AFM height images (A and B) and deflection image (C) of Marathon after microtoming. Note the pulled tabs and oriented polymer structure. This structure is known as a shish-kabob structure where crystals of UHMWPE are the kabobs and the amorphous polymer is the shish [24]. 

D. 1. Bower, Structure and Properties of Oriented Polymers AppHed Sciences, London, U.K., 1975. 

Keller, A. and Kolnaar, H.W.H. (1997) Flow-induced orientation and structure formation, in Processing of Polymers, ed. Meijer, H.E.H. Materials Science and Technology, A Comprehensive Treatment, eds. Cahn, R.W., Haasen, P. and Kramer, E.J. (VCH, Weinheim) p. 189. 

MW and MWD are very significant parameters in determining the end use performance of polymers. However, difficulty arises in ascertaining the structural properties relationship, especially for the crystalline polymers, due to the interdependent variables, i.e., crystallinity, orientation, crystal structure, processing conditions, etc., which are influenced by MW and MWD of the material. The presence of chain branches and their distribution in PE cause further complications in establishing this correlation. 

The Emerman model described in the previous section is hardly applicable to the carbon black-filled CCM as the black particles have sizes of hundreds angstrom and such a composite, compared with the molding channel size, may be considered as a homogeneous viscous fluid. Therefore, the polymer structure, crystallinity and orientation play an important role for such small particles. The above-given example of manufacture of the CCM demonstrates the importance of these factors being considered during processing of a composite material to and article with the desired electrical properties. 

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. 

Ward, I. M. Structure and properties of oriented polymers, Applied Science Publishers, London, (1975)... 

Each unit of structure in the oriented polymer will also be considered to possess transverse isotropy. Its orientation can therefore be defined by polar and azimuthal angles (0, tp), but the condition of transverse isotropy for the whole sample means that the observed second moment will depend only on functions of 0 (in fact, P200 and P400) the functions involving (p taking fixed average values. 

There has been considerable interest in the structure and properties of poly(tetra-methylene terephthalate) 4GT, stemming from the observation that when the oriented polymer is stretched, the crystalline regions are transformed from one structure to a new one30,3l). It appears from the X-ray diffraction data that in the structure... 

This discussion of the structures of diene polymers would be incomplete without reference to the important contributions which have accrued from applications of the ozone degradation method. An important feature of the structure which lies beyond the province of spectral measurements, namely, the orientation of successive units in the chain, is amenable to elucidation by identification of the products of ozone cleavage. The early experiments of Harries on the determination of the structures of natural rubber, gutta-percha, and synthetic diene polymers through the use of this method are classics in polymer structure determination. On hydrolysis of the ozonide of natural rubber, perferably in the presence of hydrogen peroxide, carbon atoms which were doubly bonded prior to formation of the ozonide... 

One of the special features is the extensive discussion and explanation of the interdependence between polymer structure, properties, and processing. The book contains numerous application-oriented examples and is presented at an intermediate level for both practicing plastics engineers and advanced engineering students. 

V.J. McBrierty and K.J. Packer, Nuclear Magnetic Resonance of Solid Polymers. Cambridge University Press, Cambridge, 1993 H.W. Spiess. In I.M. Ward (Ed.), Structure and Properties of Oriented Polymers, 2nd ed., Chapman Hall, London, 1997. 

We note here that all the information presently available on high molecular weight polymer crystal structures is compatible with the bundle model. While very nearly all crystalline polymer polymorphs involve all-parallel chain arrangements, even the only known exception, namely y-iPP [104,105], where chains oriented at 80° to each other coexist, is characterized by bilayers of parallel chains with opposite orientation. This structure is thus easily compatible with crystallization mechanisms involving deposition of bundles of 5-10 antiparallel stems on the growing crystal surface. Also the preferred growth... 

Cast film extrusion of polyolefins has been developed to obtain flexible films with a high level of transparency by freezing the amorphous polymer structure of the melt on a chill roll. Cast films are mono-oriented in extrusion direction. 

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