Crystalline Extended chain

Sect. 4.7). At the bottom of Fig. 4.25, four data points measured on semicrystalline polyethylene with different diluents are listed. They correspond well to the calorimetric value of 4.10 kJ/mole of CH2 that was measured on 100% crystalline, extended-chain polyethylene. 

Examples of polymers which form anisotropic polymer melts iaclude petroleum pitches, polyesters, polyethers, polyphosphaziaes, a-poly- -xyljlene, and polysdoxanes. Synthesis goals iaclude the iacorporation of a Hquid crystal-like entity iato the maia chaia of the polymer to iacrease the strength and thermal stabiHty of the materials that are formed from the Hquid crystal precursor, the locking ia of Hquid crystalline properties of the fluid iato the soHd phase, and the production of extended chain polymers that are soluble ia organic solvents rather than sulfuric acid. 

Similady, hquid-crystal polymers exhibit considerable order in the hquid state, either in solution (lyotropic) or melt (thermotropic). When crystallized from solution or melt, they have a high degree of extended-chain crystallinity, and thus have superior mechanical properties. Kevlar (Du Pont) is an aromatic polyamide (atamid) with the repeating unit designated as (2). It is spun into... 

Miscibility or compatibility provided by the compatibilizer or TLCP itself can affect the dimensional stability of in situ composites. The feature of ultra-high modulus and low viscosity melt of a nematic liquid crystalline polymer is suitable to induce greater dimensional stability in the composites. For drawn amorphous polymers, if the formed articles are exposed to sufficiently high temperatures, the extended chains are retracted by the entropic driving force of the stretched backbone, similar to the contraction of the stretched rubber network [61,62]. The presence of filler in the extruded articles significantly reduces the total extent of recoil. This can be attributed to the orientation of the fibers in the direction of drawing, which may act as a constraint for a certain amount of polymeric material surrounding them. 

Hence, the extension of an isotropic unoriented partially crystalline polymer leads to the formation of a highly organized material with a characteristic fibrillar structure. The anisotropy of the sample as a whole is expressed by a higher modulus, tenacity and optical anisotropy. It would seem that the increase in strength in the drawing direction suggests that the oriented samples consist of completely extended chains. However, while the strength of such perfect structure for polyethylene has been evaluated as 13000 MPas), the observed values for an oriented sample are 50 to 30 MPa. 

As compared to ECC produced under equilibrium conditions, ECC formed af a considerable supercooling are at thermodynamic equilibrium only from the standpoint of thermokinetics60). Indeed, under chosen conditions (fi and crystallization temperatures), these crystals exhibit some equilibrium degree of crystallinity at which a minimum free energy of the system is attained compared to all other possible states. In this sense, the system is in a state of thermodynamic equilibrium and is stable, i.e. it will maintain this state for any period of time after the field is removed. However, with respect to crystals with completely extended chains obtained under equilibrium conditions, this system corresponds only to a relative minimum of free energy, i.e. its state is metastable from the standpoint of equilibrium thermodynamics60,61). 

Unlike the crystalline cycloamylose complexes, combining ratios of host to guest in solution are usually 1 1. A notable exception is the interaction of the cycloamyloses with long chain aliphatic carboxylic acids. Solubility plots suggest that as many as four cycloheptaamylose molecules may interact with a single molecule of dodecanoic acid (Schlenk and Sand, 1961). In analogy to the crystalline state, cycloamyloses may form channels in solution in order to accomodate extended chains. 

The spatial size of entanglement is too large to be included within the crystalline lattice. Therefore, we can assume that the entanglements, which are expressed by cross marks in Fig. 28, can exist only on the surface of a crystal or in the amorphous layers between lamellae. Therefore, thick extended chain single crystals (ECSCs) include little entanglement (ve 0), while FCCs composed of stacked thin lamellae include a lot of entanglements (Fig. 28) [49,50]. 

A) is much smaller than the lamellar length of ordinary PE crystals ( 100A), thus the PE chains are prevented from folding. In this manner, extended-chain crystalline nanofibers of linear polyethylene with an ultrahigh molecular weight (6,200,000) and a diameter of 30 to 50 nm are formed. 

Extended-chain crystallinity, 20 398-399 Extended-DLVO theory, 21 668 Extended failures, 26 981 Extended HMO theory (EHT), 16 736 Extended patent families, 18 207 Extended shelf life (ESL) packaged products, 13 32... 

Usually, synthetic polymers crystallize11 j15 from a melt or a solution in form of folded lamellae. Under specific circumstances it is sometimes also possible to obtain extended chain crystals which is the preferred arrangement in the crystallites of many natural polymers (cellulose, silk). Recently it has been found33 31 that in some cases another crystalline modification can be obtained, the so-called shish-kebabs, which are a sort of hybrid between folded lamellae and extended chain crystals. These shish-kebabs are obtained by shear-induced crystallization, a process in which the polymer crystallizes from solution under the influence of an elongated flow. 

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