Amorphous States

Amorphous polymers convert reversibly between the rubbery and glassy states as their temperature rises or falls. Below their glass transition temperature, amorphous polymers exist in a glassy state. Above their glass transition temperature they are rubbery. We can demonstrate this easily with a racquet ball, which is made of an amorphous polymer. At room temperature, as we all know, the ball bounces at this temperature it is in the rubbery state. If we immerse the ball in liquid nitrogen it becomes brittle and will shatter when we drop it, i.e., it has become a glass. If we were to allow the frozen ball to warm up to room temperature, it would become rubbery once more. We can freeze and thaw the same ball repeatedly with no loss of its properties at room temperature. 

Rubbery amorphous polymers behave this way, and not like liquids, because their chains are not entirely free to slide past one another. The principal factors that limit long range 

Rubbery amorphous polymers do not hold their shape weU unless they are permanently crosslinked. If automobile tires were not crosslinked, they would be a soft sticky mess that would flo v under the weight of the car. For this reason, we rarely encounter rubbery amorphous polymers that are not crosslinked. 

In the glassy amorphous state polymers possess insufficient free volume to permit the cooperative motion of chain segments. Thermal motion is limited to classical modes of vibration involving an atom and its nearest neighbors. In this state, the polymer behaves in a glass-like fashion. When we flex or stretch glassy amorphous polymers beyond a few percent strain they crack or break in a brittle fashion. 

Glassy amorphous polymers exhibit excellent dimensional stability and are frequently transparent. Everyday examples include atactic polystyrene, polycarbonate, and polymethylmethacrylate (Plexiglas ), which tve encounter in such applications as bus shelters, motorcycle windshields, and compact disc cases. 

Grinding or any other deformation of a solid causes crushing and disorganization of crystal grains, generation of defects, dislocations, micro-cracks, and ultimately amorphization of the crystalline material. The question arises to what size it is possible to grind a crystal in order for its properties still to correspond to those of the bulk material, and where is the size border between a crystal and an amorphous body  

Some oriented polymers only exhibit sharp X-ray diffractions at the equator. In such cases, the macromolecules must be packed in two-dimensional lateral order. However, the monomeric units in each polymer chain are randomly arranged, because of either a random displacement of polymer chains with respect to their neighbors, or a random distribution of monomeric units within each chain or because of irregular chain structure with respect to tacticity. Poly(acrylonitrile) is an example of the last case, and poly(ethylene-/7-carboxyphenoxyundecanoate) is an example of the first case. 

Finally, it is possible that side chains in polymers with very long side chains occur in mesomorphous structures, whereas the main chain is amorphous below the glass transition temperature, and behaves like a normal liquid above it. This type of behavior is observed when the movements of the main and side chains are decoupled by flexible spacer groups joining them together. An example of this is a poly(methacrylate) with the monomeric unit  

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Cryoinnnobilization procedures tiiat lead to vitrification (immobilization of the specimen water in the amorphous state) are the sole methods of preserving the interactions of the cell constituents, because the liquid character of the specimen water is retained (reviewed in [25]). 

This last interpretation makes P(0) the same as the fraction of a sample in the amorphous state. It is conventional to focus on the fraction crystallized 6 therefore the fraction amorphous is I - 6 and... 

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

Crystallinity is low the pendent allyl group contributes to the amorphous state of these polymers. Propylene oxide homopolymer itself has not been developed commercially because it cannot be cross-baked by current methods (18). The copolymerization of PO with unsaturated epoxide monomers gives vulcanizable products (19,20). In ECH—PO—AGE, poly(ptopylene oxide- o-epichlorohydrin- o-abyl glycidyl ether) [25213-15-4] (5), and PO—AGE, poly(propylene oxide-i o-abyl glycidyl ether) [25104-27-2] (6), the molar composition of PO ranges from approximately 65 to 90%. 

Poly(ethylene terephthalate) film is produced by quenching extruded film to the amorphous state and then reheating and stretching the sheet approximately three-fold in each direction at 80-100°C. In a two-stage process machine direction stretching induces 10-14% crystallinity and this is raised to 20-25% by... 

Amorphous stereotactic polymers can crystallise, in which condition neighbouring chains are parallel. Because of the unavoidable chain entanglement in the amorphous state, only modest alignment of amorphous polymer chains is usually feasible, and moreover complete crystallisation is impossible under most circumstances, and thus many polymers are semi-crystalline. It is this feature, semicrystallinity, which distinguished polymers most sharply from other kinds of materials. Crystallisation can be from solution or from the melt, to form spherulites, or alternatively (as in a rubber or in high-strength fibres) it can be induced by mechanical means. This last is another crucial difference between polymers and other materials. Unit cells in crystals are much smaller than polymer chain lengths, which leads to a unique structural feature which is further discussed below. 

Low shrinkage - all thermoplastics are processed in the amorphous state. On solidification, the random... 

Further developments in this area have included the neparation of several additional N,N -diaryl indolo[3,2-h]carbazoles with substituents such as m-tolyl, ffi-anisoyl, or triarylamine-containing species. Like 221, these compounds, possessing excellent hole-transport properties, also occurred in stable amorphous states and displayed high glass-transition temperatures. LED devices involving these systems were also constructed and showed promising characteristics [OOSMO11-112)42]]. 

Crystallization The formation of crystallites or groups of plastic molecules in an ordered structure within the plastic as the plastic is cooled from its amorphous state to a temperature below its crystallization temperature. 

Supercooling The rapid cooling of a normally crystalline plastic through its crystallization temperature, so it does not get a chance to crystallize and it remains in the amorphous state. 

Fig. 12. Free energy vs. temperature for FCC-cttrve /, for ECC-curve II and for the amorphous state (melt)-cur-ve III. Points 1 and 2 represent the melting temperatures of FCC and ECC, respectively, point 3 separates the ranges of the predominant existence of FCC and ECC (see text)...

Dependence on Density.—If the density of a metal is increased by hammering, its specific heat is slightly decreased. The same change is observed if the change of density is due to a change of crystalline form, or to change from an amorphous state to a crystalline state, and with different allotropic forms (Wigand, loc. cit,). 

The amorphous state frequently passes spontaneously into the crystalline state (plastic sulphur, devitrification of glass, Gore s amorphous antimony). 

In the studies that attribute the boundary friction to confined liquid, on the other hand, the interests are mostly in understanding the role of the spatial arrangement of lubricant molecules, e.g., the molecular ordering and transitions among solid, liquid, and amorphous states. It has been proposed in the models of confined liquid, for example, that a periodic phase transition of lubricant between frozen and melting states, which can be detected in the process of sliding, is responsible for the occurrence of the stick-slip motions, but this model is unable to explain how the chemical natures of lubricant molecules would change the performance of boundary lubrication. 

Coupling the motion of the mosaic cell (TLS and boson peak) to phonons is necesssary to explain thermal conductivity therefore the interaction effects discussed later follow from our identification of the origin of amorphous state excitations. The emission of a phonon followed by its absorption by another cell will give an effective interaction, in the same way that photon exchange leads to... 

This difference in spatial characteristics has a profound effect upon the polymer s physical and chemical properties. In thermoplastic polymers, application of heat causes a change from a solid or glassy (amorphous) state to a flowable liquid. In thermosetting polymers, the change of state occurs from a rigid solid to a soft, rubbery composition. The glass transition temperature, Tg, ... 

Blends of enzymatically synthesized poly(bisphenol-A) and poly(p-r-butylphenol) with poly(e-CL) were examined. FT-IR analysis showed the expected strong intermolecular hydrogen-bonding interaction between the phenolic polymer with poly(e-CL). A single 7 was observed for the blend, and the value increased as a function of the polymer content, indicating their good miscibility in the amorphous state. In the blend of enzymatically synthesized poly(4,4 -oxybisphenol) with poly(e-CL), both polymers were miscible in the amorphous phase also. The crystallinity of poly(e-CL) decreased by poly(4,4 -oxybisphenol). 

The results of the XRD measurement showed that the Fe jAl, jPO catalyst was almost in amorphous state. Only a very broad peak at 29 of ca. 23 degree was observed. The Mossbauer spectroscopic study on this catalyst showed one doublet of iron with the isomeric shift of 0.31 mm s (a-Fe was used as the reference) and the quadrupole splitting of 0.62 mm s. These parameters are very close to those observed for FePO [13, 14], suggesting that the iron cation in the catalyst is tetrahedrally coordinated with oxygen and isolated by four PO tetrahedral units. Such coordination circumstance was suggested to be a key factor for the iron site effective for the oxidation of CH to CHjOH by H -Oj gas mixture [15]. 

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