Polymers amorphous state

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 britde fashion. 

Behavior in the Amorphous State. Polymer behavior in the amorphous state can be divided into two categories the glassy state and the fluid state. The former applies to pol5uners below the glass transition and is generally dominated by the segmental or local movements of the polymer chains. The fluid state of the... 

The experimental observation of the same Gaussian statistics of polymer chains in 0-solvent and condensed state is the main objection against local order availability in amorphous state polymers [105]. The equality of distances between macromolecules or subchains ends in the indicated states is considered as one of the pieces of evidence of this rule. Boyer [106] demonstrated schematically the possibility of local order existence at fulfilment of the indicated condition. However, strict confirmation of such a possibility was not obtained. Therefore the authors of paper [107] confirmed analytically Boyer s concept on the example of two series of epoxy polymers (EP-1 and EP-2). 

The model of free volume going back to the classical papers of Frenkel and Firing [48, 80, 144-147] has been widespread in the physics of liquid and solid states of matter. Some concepts allowing improvement in the nature of fluctuation free volume have been offered in the last 15 years [148-150]. Nevertheless, there is one more aspect of the problem, which has not been mentioned earlier. As a rule, the application of free volume theory for the description of the properties of amorphous bodies is based on a notion that the free volume characterises the structure of the indicated bodies. This postulate is due to a considerable extent to the absence of a quantitative model of the structure of the amorphous condensed state, including the structure of amorphous state polymers. Strictly speaking, one should understand that by structure we mean distribution of body elements in space [151]. It is evident that free volume microvoids cannot be structural elements and at best only mirror the structural state of the studied object. Taking the introduction of some structural elements (relaxators, see for example, [148]) into consideration has practically no influence on the structural representation of free volume. 

For amorphous state polymers the values of Lf and are identified as follows. DS, forming in the mentioned state, are clusters [143]. The cluster model [5,6] postulates that the length of segments, included in a cluster, is equal to the statistical segment length and therefore Z =/ [93] (see also Equation 5.54). One should accept the distance between clusters as the next structural scale and therefore Z = [93]. 

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%. 

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. 

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). 

Solid polymers can adopt a wide variety of structures, all of which are derived from the three basic states rubbery amorphous, glassy amorphous, and crystalline. Either of the amorphous states can exist in a pure form. However, crystallinity only occurs in conjunction with one of the amorphous states, to form a semicrystalline structure. 

In the molten state polymers are viscoelastic that is they exhibit properties that are a combination of viscous and elastic components. The viscoelastic properties of molten polymers are non-Newtonian, i.e., their measured properties change as a function of the rate at which they are probed. (We discussed the non-Newtonian behavior of molten polymers in Chapter 6.) Thus, if we wait long enough, a lump of molten polyethylene will spread out under its own weight, i.e., it behaves as a viscous liquid under conditions of slow flow. However, if we take the same lump of molten polymer and throw it against a solid surface it will bounce, i.e., it behaves as an elastic solid under conditions of high speed deformation. As a molten polymer cools, the thermal agitation of its molecules decreases, which reduces its free volume. The net result is an increase in its viscosity, while the elastic component of its behavior becomes more prominent. At some temperature it ceases to behave primarily as a viscous liquid and takes on the properties of a rubbery amorphous solid. There is no well defined demarcation between a polymer in its molten and rubbery amorphous states. 

The density of the rubbery amorphous state is only slightly higher than that of the molten state, the difference being attributable to reduced thermal motion of its chains. In this loosely packed condition, the polymer incorporates a substantial amount of molecular scale void... 

Each crystallizable polymer exhibits a characteristic equilibrium melting temperature, at which the crystalline and amorphous states are in equilibrium. Above this temperature crystallites melt. Below this temperature a molten polymer begins to crystallize. 

Secondary crystallization occurs most readily in polymers that have been quench-cooled. Quenched samples have low degrees of crystallinity and thus have relatively large volumes of amorphous material. A pre-requisite for secondary crystallization is that the amorphous regions must be in the rubbery amorphous state. Increased temperature accelerates the rate of secondary crystallization. The new volumes of crystallinity that form during secondary crystallization are generally quite small, amounting to less than 10% of the crystalline volume created during primary crystallization. 

Finally, we were led to the last stage of research where we treated the crystallization from the melt in multiple chain systems [22-24]. In most cases, we considered relatively short chains made of 100 beads they were designed to be mobile and slightly stiff to accelerate crystallization. We could then observe the steady-state growth of chain-folded lamellae, and we discussed the growth rate vs. crystallization temperature. We also examined the molecular trajectories at the growth front. In addition, we also studied the spontaneous formation of fiber structures from an oriented amorphous state [25]. In this chapter of the book, we review our researches, which have been performed over the last seven years. We want to emphasize the potential power of the molecular simulation in the studies of polymer crystallization. 

Direct evidence of nucleation during the induction period will also solve a recent argument within the field of polymer science as to whether the mechanism of the induction of polymers is related to the nucleation process or to the phase separation process (including spinodal decomposition). The latter was proposed by Imai et al. based on SAXS observation of so-called cold crystallization from the quenched glass (amorphous state) of polyethylene terephthalate) (PET) [19]. They supposed that the latter mechanism could be expanded to the usual melt crystallization, but there is no experimental support for the supposition. Our results will confirm that the nucleation mechanism is correct, in the case of melt crystallization. 

Packing efficiency can also be described by the extent of short-range order in the amorphous state. Mitchell has shown through X-ray scattering studies that, while the local molecular organization of noncrystalline polymers is random, in many cases, there are additional correlations that do not perturb the chain trajectory but will impact polymer properties.15 These correlations have a limited spatial range (<50A) but will have a particular impact on bulk properties... 

G. Mitchell, Order in the Amorphous State of Polymers, Plenum Press, New York (1986). 

The infrared absorption spectra of the same polymer in the crystalline and amorphous states may differ because of the following two reasons (i) Specific intermolecular interactions may exist in the crystalline polymer which lead to sharpening or splitting of certain bands and (ii) Some specific conformations may exist in one but not the other phase, which may lead to bands characteristic exclusively of either crystalline or amorphous material. For example in polyethylene terepthalate), the 0CH2CH20 portion of each repeat unit is restricted to the all trans-conformation in the crystal, but... 

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