Semicrystalline polymer systems

Fourier transform infrared imaging allows for the examination of semicrystalline polymers via their dichroism.31 Typical images of the center of a PEG (Mw35k, Tc 35°C) spherulite are shown in Fig. 5.15. These images were generated by plotting the baseline corrected absorbance intensity of the 1343 cm-1 CH2 wagging 

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Brockmeier, N. F. McCoy, R. W. Meyer, J. A., "Gas Chromatographic Determination of Thermodynamic Properties of Polymer Solutions. II. Semicrystalline Polymer Systems," Macromolecules, 6, 176 (1973). 

In order for the ordered phase to crystallize from an amorphous melt a nucleation barrier must be overcome. This barrier is a result of interfacial energy between the ordered phase and the melt that causes super cooling. Sirota [44] suggested that in order for the nucleation barrier of the stable phase to be sufficiently high to form out of the melt, another phase with a lower nucleation barrier and a free energy intermediate between that of the stable phase and the melt must form. This, he points out, is implied by Oswald s rule [45] and evidence presented by Keller [35] that crystallization in semicrystalline polymer systems is mediated by a transient metastable phase [47, 48]. 

FIGURE 5.2.3 Classification of soft shape-memory materials from the viewpoint of nanoaivhitectonics. (a-c) Structures and (d) molecular mechanism, (a) Chemically cross-linked polymer network, (b) supramolecular network with clay nanosheets [29], and (c) inorganic/polymer composite network system, and their shape-memory profiles [30]. (d) The nanoscale molecular mechanism for one-way and two-way SME of a cross-linked semicrystalline polymer system. 

Although this index has been developed to describe drug-PEG eutectic systems, it is expected to apply with reasonable accuracy in a variety of similar drug-semicrystalline polymer systems. 

Yan S, Petermann J, Yang D. Epitaxial crystallization in the sPP/nylon-12 semicrystalline polymer system. Polymer 1996 37 2681-2685. 

Several examples, including polyethylene (PE), poly(trimethylene terephthalate) (PTT, poly(butylene terephthalate) (PBT), poly(lactic acid) (PLA), and others are shown in order to present the rationale behind quantitative thermal analysis of melting in several semicrystalline polymer systems. 

The model has also been found to work well in describing the mechanics of the interface between the semicrystalline polymers polyamide 6 and polypropylene coupled by the in-situ formation of a diblock copolymer at the interface. The toughness in this system was found to vary as E- where E was measured after the sample was fractured (see Fig. 8). The model probably applied to this system because the failure occurred by the formation and breakdown of a primary craze in the polypropylene [14],... 

Aprotic polar solvents have to be used for several reasons. They are often good solvents for both monomers (including phenolates) and amorphous polymers. In addition, they can also stabilize the Meisenheimer intermediates. Common aprotic polar solvents, such as DMSO, /V,/V-dimcthyl acetamide (DMAc), DMF, N-methyl pyrrolidone (NMP), and cyclohexylpyrrolidone (CHP) can be used. Under some circumstances, very high reaction temperature and boiling point solvents such as sulfolane and diphenyl sulfone (DPS) have to be used due to the poor reactivity of the monomers or poor solubility of the resulting, possibly semicrystalline polymers, as in the PEEK systems. 

The crystallization process of flexible long-chain molecules is rarely if ever complete. The transition from the entangled liquid-like state where individual chains adopt the random coil conformation, to the crystalline or ordered state, is mainly driven by kinetic rather than thermodynamic factors. During the course of this transition the molecules are unable to fully disentangle, and in the final state liquid-like regions coexist with well-ordered crystalline ones. The fact that solid- (crystalline) and liquid-like (amorphous) regions coexist at temperatures below equilibrium is a violation of Gibb s phase rule. Consequently, a metastable polycrystalline, partially ordered system is the one that actually develops. Semicrystalline polymers are crystalline systems well removed from equilibrium. 

Basic Equations. Scattering according to Porod s law [18,137] is a consequence of phase separation in materials. In a two-phase system (e.g., a semicrystalline polymer) every point of the irradiated volume belongs to one of two distinct phases (in the example to the crystalline phase or to the amorphous phase). In a multiphase system there are more than two distinct phases. 

They produced high performance electrets from thin polymer films metallized so as to yield high capacitance. Both electrical and mechanical properties of these transducers have been remarkable examples of how applications of science of solids, including knowledge of electron traps, conduction processes in insulators and the viscoelastic phenomena of semicrystalline polymers, can be combined.(6) Incidentally, similar ideas have been applied to optimization of the properties of particle microphones, through assemblies of perfectly microspherical polymer carbon systems. These have shown what limits of performance... 

It is of course important to note that the overall rate of crystallization is not only determined by the growth rate of the spherulites, but also by the amount of nuclei being present in the system. This possibility is used as an effective method to influence the total crystallization rate of commercial polymeric materials in a controlled manner and to influence the size of spherulites and thus the physical properties of finished articles made from semicrystalline polymers. 

Most radiation graft polymerizations are carried out as heterogeneous reactions. The polymer is swollen by monomer but does not dissolve in the monomer. (For semicrystalline polymers, swelling and grafting take place only in the amorphous regions.) The typical reaction system involves equilibration of polymer with monomer followed by irradiation of the... 

Absorbance subtraction can be considered as a spectroscopic separation technique for some problems in polymers. An interesting application in FT-IR difference spectroscopy is the spectral separation of a composite spectrum of a heterophase system. One such example is a semicrystalline polymer which may be viewed as a composite system containing an amorphous and crystalline phase53). In general, the infrared spectrum of each of these phases will be different because in the crystalline phase one particular rotational conformation will predominate whereas in the disordered amorphous regions a different rotamer will dominate. Since the infrared spectrum is sensitive to conformations of the backbone, the spectral contributions will be different if they can be isolated. The total absorbance A, at a frequency v of a semicrystalline polymer may be decomposed into the following contributions... 

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