Crystallization behaviors of a and

Crystallization Behaviors of a- and P-Quizalofop-ethyl Polymorphs in Homogeneous Nucleation... 

With the details associated with ADMET chemistry reasonably well understood, we have embarked on a study of the synthesis of well-controlled polymer structures via metathesis polycondensation chemistry [37]. A series of well-defined polyolefins have been designed to model the crystallization behavior of polyethylene and its related copolymers, including new materials synthesized by metallocene-based catalysts. This synthesis concept has been reduced to practice, and polymers that will aid in the understanding of branching within polyethylene itself have been produced. 

Fat crystallization has been extensively studied in bulk fats and, to a lesser extent, in emulsified fats. It has been shown that the crystallization behavior of a fat will proceed quite differently, depending on whether it is in bulk or emulsified form (4,5). Authors have examined the effect of the state of dispersion on the crystallization mechanisms (nucleation, crystallization rate) and polymorphic behavior (6-11) of partial- and triglycerides in bulk and emulsified form. Understanding the mechanisms of emulsion nucleation and crystallization is one of the first steps in understanding the destabilization of emulsions and partial coalescence, e.g., stabilization of liquid fat emulsions by solid particles (fat) or control of the polymorphic form of crystals during the process of partial coalescence to control the size of aggregates and textural properties. 

There are occasions when even the most intense efforts to crystallize a specific protein fail despite the best efforts at ultra-purification and elimination of microheterogeneity. When this occurs, an alternative is to turn to a different source of the protein. Often only very small variations in amino acid sequence, as found for example between different species of organisms, is enough to produce dramatic differences in the crystallization behavior of a protein. Thus, if the protein from one source proves intractable, consider another. With recombinant proteins, of course, one always has the option of producing a vast range of mutants. Variation of sequence in fact provides a powerful approach to crystallizing proteins when the native molecule fails. There is currently much work underway to define effective mutation strategies for protein crystallization (Derewenda, 2004 Dale et al., 2003). 

Fig. 4.6. Crystallization behavior of amorphous and partially oxidized Nie4Zr3e alloy investigated by DSC measurements. Curve A was measured for as-quenched amorphous alloy, a denotes the degree of oxidation of the sample. Heating rate 5 K/min...

An interesting application of the direct relationship between nucleating interfaces and the total amount of the interfacial contact surface can be found in compatibilized immiscible blends. In these systems, the dispersed phase size becomes much smaller, strongly increasing the total amount of interface at which nucleation can occur. Some authors reported that this could cause an upward shift in the by up to 10°C [Wei-Berk, 1993]. However, other studies in which the crystallization behavior of a compatibilized blend was investigated did not always mention such a clear nucleating activity (Table 3.17). 

The irradiation of alcohols, acids, amides, fluorocarbons, and other compounds has provided other radicals for study. Work on single crystals oriented in magnetic fields yielded the spectroscopic data for the perfluorosuccinate, XX, and the perfluoropropionamide, XXVI (51,56). The study of unoriented materials has yielded additional information concerning the coupling behavior of a-and /3-fluorine atoms in perfluoromethylcyclohexyl radical, XXVII, hydroxyalkyl derivatives, XXVIII, the perfluoroglutarate, XXIX (57,58) as well as the 2,2,2-trifluoroethyl radical (59) and other related substances (54). 

Sun L, Liu YX, Zhu L, Hsiao BS, AvUa-Orta CA (2004) Self-assembly and crystallization behavior of a double-crystalline polyethylene-block-poly(ethylene oxide) diblock copolymer. Polymer 45 8181-8193... 

A large number of polymer blends contain one or two crystallizable components. The crystallization behavior of a polymer component in a blend is expected to be altered by the presence of the second blend component, whether both are completely miscible, partially miscible, or totally immiscible. Therefore, a profound scientific understanding of the crystallization behavior and the resulting semicrystalline structure in polymer blends is necessary for effective manipulation and control of their properties. 

Fig. 3.5 Model describing the crystallization behavior of (a) 80/20 PEO/Aramide 341 blend (b) after fast primary crystallization (c) secondary crystallization and (d) a 65/35 PEO/Aramide blend after crystallization (Dreezen et al. 1999)...

Nucleating efficiency is normally determined isothermaUy from crystallization half-time, by use of peak crystallization temperature of the nucleated system measured during cooling and compared with that of the neat polymer. The peak crystallization temperature technique is based on a single-point observation. FDlon et al. proposed alternate approach for the evaluation of nucleating efficiency using two dynamic reference points to understand the crystallization behavior of a polymer (FOlon et al. 1993). These two reference points include (i) polymer s crystallization temperature when crystallized normally and (ii) the same when polymer nucleated ideally. 

It has been well documented that the crystallization behavior is dependent on the processing conditions and inherent crystallization behavior of the polymer. The inherent crystallization behavior of a polymer is known to depend on its molecular architecture defined in terms of linearity, molecular-weight distribution (M WD), and degree of branching. In the case of PPS, the effects of these parameters on the crystallization behavior has been a subject of interest and these will be discussed in the next sections. 

In this work, the structure, morphology and crystallization behavior of a semi-crystalline polymer, poly(ethylene oxide), PEO, when mixed with natural montmorillonite (Na -MMT) are studied [9]. The structure of the hybrids was investigated by X-ray diffraction (XRD), the thermal properties by Differential Scanning Calorimetry (DSC) and the kinetics of crystallization by isothermal Polarized Optical Microscopy (POM) and isothermal DSC. It is known that for PEO /... 

The crystallization behavior of PA6 and its nanocomposites undergoing a microcellular injection molding process was studied using TEM, XRD, SEM, and PLM the addition of polarized light microscopy was important to study crystal formation [492]. A synthesis approach to make PP nanocomposites by in situ polymerization was studied by OM, TEM, and... 

Su et al. [30] also performed direct and nonintrusive observations of crystallization and melting behavior of a and p polymorphs in bulk SPS by means of temperature-programmed X-ray diffraction. Results indicated that the perfection of the less ordered a form into the better ordered a" form within the a family occur in the vicinity of 270 °C. 

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