Molten state, of polymers

The first term of Eq 2.48 is the H-F combinatorial entropy. The second term (where the subscript v indicates the free volume fraction) represents the free volume contribution to the entropy of mixing. The third term represents the non-combinatorial contribution [g ((t) ) is the non-combinatorial energy on a molten state of polymer i having the free volume fraction (()y]. The fourth term represents the energetic contribution originating from interaction between unlikely species, i j. Here gj.( (()j ) is the interaction term expressed as polynomial with coefficients that depend on the structure of the polymer chains. These coefficients are computed as double expansions in 1/z ( z is the lattice coordination number), and e jj/kgT (e j is the van der Waals interaction energies between groups a and b). 

Fig. 19.18. Schematic illustration for cooling process in crystallization of PESU. At the first stage of cooling process, the molten state of polymer sample at 135° C is cooling down to a certain setup temperature (Tset) with the cooling rate of ISO C/min. And successively, the cooling rate is changed at Tset to 10°C/min from 130°C/min then holds at a given crystallization temperature (Tc)...

The production of micron-sized polymer powders fi om molten polymers is an attractive, facile, low energy, and economic process. Polymer powders with tailored characteristics such as particle shape, size distribution, and purity can be directly prepared from the molten state of polymers such as polyethylene-based waxes that can not be ground using conventional methods [10-12,46,83-84]. The Gas Atomization Process (GAP) for mass-producing high quality spherical... 

The molten state of polymers is more dependent on the molar mass than any of their other physical states. Flexible-chain polymer molecules possess essentially random conformations in the molten state. The coiled molecules entangle in high molar mass polymers. These chain entanglements are very important for the rheological properties of the melt. The next part of this chapter (section 6.4) deals with the rheology of flexible-chain polymer melts. A discussion of the deformation mechanisms, including theoretical aspects, is also presented. 

Such a special conformation of molecules cannot be assumed without reservation. Nevertheless, the molecular conformation in the noncrystalline region is unlikely to be the same in detail as that of the completely molten state of the polymers. Since a molecular chain in the structure generally participates in both the crystalline and the noncrystalline regions, molecular mobility in the noncrystalline region will be more or less restricted by the presence of the crystalline region. 

When an amorphous polymer achieves a certain degree of rotational freedom, it can be deformed. If there is sufficient freedom, the molecules begin to move past one another and the polymer flows. The science of deformation and flow is called rheology. It is of fundamental importance in industrial applications since it is usually in the molten state that polymers are molded into usefid objects. 

The irradiation of fluoropolymers at elevated temperatures has been explored for the development of materials with better mechanical properties [35]. This arises because of the radiation-induced crossUnking of chains and subsequent higher network density in the resultant polymer [36]. Here, the irradiation is accomplished at a temperature higher than the melting point of the polymer. In the molten state, the polymer behaves as an amorphous matrix and the mobility of molecular chains is considerably enhanced. This promotes the mutual recombination of radicals, i.e., crossHnking involving chain end radicals and chain alkyl radicals [37]. 

Endo et al. reported a synthesis ofpoly(l,2-dithiane) (PDT) [151,152] that possibly contained polycatenane structures (Scheme 17.24). A melt polymerization [153] of 1,2-dithiane 84, without initiators, yielded the polymer 85, the NMR analysis of which confirmed the presence of large cyclic structures, which were further verified using by mass spectroscopy and photodegradation analysis. In addition, dynamic viscoelastic measurements showed that the molten state of the polymer 85 has a rabbery plateau, while the Tg of PDT decreased with increasing molecular weight. These observations, which differed from those obtained with the linear PDT analog, provided further evidence for the formation of polycatenane structures. In taking... 

Transitions are treated in the general physical chemistry references of Sect. 2.3. See also Ubbelohde AR (1965 and 1978) Melting and Crystal Structure. Oxford University Press, London, and The Molten State of Matter, Melting and Crystal Structure. Wiley, New York Boyer RF (1977) Transitions and Relaxations, in Enc Polymer Sci and Technol Suppl 2. Wiley, New York an update was given in the second edition of the encyclopedia by Bendler JT (1989) under the same title, Vol 7, p 1. 

Hashmi, S.A.R. and Kitano, T. (2007) Shear rate dependence of viscosity and first normal stress difference of LCP/PET blends at solid and molten states of LCP.J. Appl. Polym. Sd 104 (4), 2212-2218. 

Unlike polycondensation polymers, polymers of addition polymerization such as polyethylene and polypropylene when depolymerized in inert atmosphere (39) or in supercritical water (37) do not convert to just the monomer, but a homologous series of oligomers (alkanes and alkenes). Compared to pyrolysis in argon, for polyethylene, the portion of the lighter products increases in supercritical water depolymerizations conducted at 693 K and water densities of 0.13 and 0.42 g/cm. The 1-alkene to n-alkane ratio also increases in supercritical water and with density. These are shown in Figure 11. These results are attributed to the fact that in argon pyrolysis, the reaction proceed in the molten state of the polymer, whereas in supercritical water, some of degradation products... 

We have now reviewed three types of behaviour the enthalpic elasticity of rigid polymers at temperatures below Tg, the entropic elasticity of polymers at temperatures above Tg- -40°C and the viscous response of uncrosslinked polymers in the molten state. When examining the various states of polymer materials, we emphasised analogies between temperature and time behaviour. This naturally leads us to consider the viscoelastic character exhibited by polymers under certain conditions, particularly in the region of the glass transition. 

In their molten states, thermoplastic polymers behave like incompressible viscous fluids. By simply melting the matrix polymer and applying moderate forces, complex geometries can often be formed, even in the presence of fibers. Furthermore, it is interesting to note that polypropylene remains deformable over a wide temperature window while cooling from its melt temperature, before it recrystallizes. In this thermal region, it exhibits nonlinear viscoelastic fluid properties which are not... 

The high-resolution capability of 2D IR spectroscopy to differentiate highly overlapped crystalline and amorphous IR bands has been successfully employed for the characterization of many other semicrystalline polymers. Biodegradable poly(hydroxyalkanoate)s, for example, were studied by this technique to show that molecular defects created by the incorporation of comonomer units tend to accumulate in the amorphous regions [49] in a manner similar to the case of linear low-density polyethylene. Additives, such as plasticizers, which are miscible in the molten state of semicrystalline polymers also tend to be excluded from the crystal lattice and preferentially accumulate in the amorphous phase once the polymer is brought down to a temperature below the melt temperature. 

In this case, we have an electrolyte identical to that which is present in lithium-polymer batteries, made of poly(ethylene oxide) (or PEO) in the presence of a lithium salt, solid at ambient temperature, and which needs to be heated above ambient temperature in order for the battery to work (T > 65°C for PEO). Thus, the electrolyte, in its molten state, exhibits sufficient ionic conductivity for the lithium ions to pass. This type of electrolyte can be used on its own (without a membrane) because it ensures physical separation of the positive and negative electrodes. This type of polymer electrolyte needs to be differentiated from gelled or plasticized electrolytes, wherein a polymer is mixed with a lithium salt but also with a solvent or a blend of organic solvents, and which function at ambient temperature. In the case of a Li-S battery, dry polymer membranes are often preferred because they present a genuine all solid state at ambient temperature, which helps limit the dissolution of the active material and therefore self-discharge. Similarly, in the molten state (viscous polymer), the diffusion of the species is slowed, and there is the hope of being able to contain the lithium polysulfides near to the positive electrode. In addition, this technology limits the formation of dendrites on the metal lithium... 

Only the molten state of linear high polymers can be called with some certainty an equilibrium state which is independent of thermal history. Its heat capacity is still caused, for the largest part, by molecular vibration. In additum, conformational changes and internal rotations are possible and need to be accounted for. In general, little is known about the detailed motion in the liquid state as it applies to the l t capacities. Only liquid polyethylene melt has been analyzed in scane detail [Wunderlidi (19 )]. 

Hashimi S, Takeshi K (2007) Shear rate dependence of viscosity and first nramal stress difference of LCP/PET blends at solid and molten states of LCP. J Appl Polym Sd 104 2212-2218 Hsies TT, Tiu C, Simon GP, Wu RW (1999) Rheology and miscibilily of thermotropic liquid crystalline polymer blends. J Non-Newt Fluid Mech 86 15-35 Isayev A1 (2012) Liquid crystalline composite. In Luigi N, Borzacchiello A (eds) Wiley Encyclopedia of composites, 2nd edn. Wiley, New York Isayev AI, Nicolais L (2011) Liquid crystalline composite. Wiley Encyclopedia of composites. Wiley, New York... 

The semicrystalline, ethylene-based ionomers of commerce are flexible, transparent polymers notable for high strength and elasticity in both soUd and molten states. The ionic bonding is completely reversible (8) and has a strong influence on properties, even at temperatures well above the melting point. 

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