Semicrystalline materials

Neither poly(ethylene 2,6-naphthoate) (PEN), nor copolymers of PEN and PET, are new materials, but they continue to receive considerable attention, due to their relatively high Tm and T values, and attractive tensile, flexural and gas-barrier 

The isomeric bibenzoic acids (BBs), would appear to share similar structural features with naphthalene dicarboxylic acid. Like the PET-naphthalate copolymers, PET-bibenzoates have been demonstrated to possess moduli and glass transitions temperatures which increase with increasing levels of rigid comonomer [37-39], Unlike the PET/PEN copolymers, when the symmetrical 4,4 - I f I f monomer is substituted into a PET backbone, virtually every composition of PET-BB is semicrystalline the 2,4- and 3,4- isomers of BB, when 

Polymer/copolymer Tensile strength (MPa) Flexural modulus (GPa) 

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Physical Form. Eor compounders, physical form is an important characteristic. They prefer sohd, free-flowing, nondusty materials whereas polymer manufacturers prefer materials that are Hquid and easily emulsified. Undesirable are semicrystalline materials which may stratify during storage. Also, substances to be avoided are highly viscous Hquids and low melting resins which block upon storage. 

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

Aromatic-aliphatic polyesters, in which either R1 or R2 is aromatic, are generally high-melting (150-270°C) semicrystalline materials that find applications as engineering thermoplastics, films, or fibers. 

The most important AA-BB-type polymer is PA-6,6. It is a semicrystalline material and has a high melting temperature (265°C). PA-6,6 is prepared from 1,6 hexamethylenediamine and adipic acid (Eq. 3.27) ... 

In the small-angle X-ray scattering (SAXS) regime the typical nanostructures (in semicrystalline materials, thermoplastic elastomers) are observed. Because of the long distance between sample and detector time-resolved measurements can only be carried out at synchrotron radiation sources (Sect. 4.2.1.2). 

For semicrystalline isotropic materials a qualitative measure of crystallinity is directly obtained from the respective WAXS curve. Figure 8.2 demonstrates the phenomenon for polyethylene terephthalate) (PET). The curve in bold, solid line shows a WAXS curve with many reflections. The material is a PET with high crystallinity. The thin solid line at the bottom shows a compressed image of the corresponding scattering curve from a completely amorphous sample. Compared to the semicrystalline material it only shows two very broad peaks - the so-called first and second order of the amorphous halo. 

It is obvious that the semicrystalline material contains this amorphous feature as well - underneath the reflections. In the semicrystalline material the halo is shifted... 

FIGURE 5.16 Spontaneous ordering of linear polymers in a semicrystalline material. Bundles of dark lines represent crystalline regions. Reprinted from Flory (1953) Paul J. Flory, Principles of Polymer Chemistry, Copyright 1953 Cornell University Press and Copyright 1981 Paul J. Flory. Used by permission of the publisher, Cornell University Press. 

Aromatic polyketones are semicrystalline materials that contain both ketone groups generally flanked by aromatic units. Many also have within them ether moieties that allow for some flexibility and better processing. They have good thermal stabilities, as well as offering good mechanical properties, flame resistance, impact resistance, and resistance to the environment. 

Although PS is largely commercially produced using free radical polymerization, it can be produced by all four major techniques—anionic, cationic, free radical, and coordination-type systems. All of the tactic forms can be formed employing these systems. The most important of the tactic forms is syndiotactic polystyrene (sPS). Metallocene-produced sPS is a semicrystalline material with a of 270°C. It was initially produced by Dow in 1997 under the trade name Questra. It has good chemical and solvent resistance in contrast to regular PS that has generally poor chemical and solvent resistance because of the presence of voids that are exploited by the solvents and chemicals. 

In most cases, however, polymers crystallize neither completely nor perfectly. Instead, they give semicrystalline materials, containing crystalline regions separated by adjacent amorphous phases. Moreover, the ordered crystalline regions may be disturbed to some extent by lattice defects. The crystalline regions thus embedded in an amorphous matrix typically extend over average distances of 10-40 nm. The fraction of crystalline material is termed the degree of crystallinity. This is an important parameter of semicrystalline materials. 

Linear [ ]-pol3turethane derived from 1-deoxy-l-isocyanate-2,3 4,5-di-(9-iso-propylidene-D-galactitol (prepared from 48) in the presence of TEA or Zr(acac)4, as well as its corresponding polyhydroxy derivative obtained by hydrolysis of the acetal protecting group, have been prepared [117]. They are semicrystalline materials that exhibit high melting temperatures and thermal stability up to 230°C. 

Galbis and co-workers [113] also obtained a polyurea 100 by polyaddition reaction of the diaminopentitol 39 with 1,6 hexamethylene diisocyanate (HDI). This polymer was a semicrystalline material that showed high melting temperature and thermal stability up to 250°C. 

Several poly(urea urethane) oligomers 28 (Figure 12) were prepared by one-component polycondensation of iV-(hydroxyalkyl)-2 -oxo-1,3-diazepane-l-carboxamides, which act as intramolecular blocked isocyanates <2005PLM 1459>. These oligomers are semicrystalline materials and their melting points show the odd/even effect observed earlier for [ ]-polyamides, [ ]-polyurethanes, poly(ester amide)s, and poly (amide urethane)s. Further analysis showed that the polymers are stable up to ca. 205-230 °C, the polymers with the lower number of methylene groups in the amino alcohol decomposing at the lowest temperature. 

Figure 1.26 summarizes the property behavior of amorphous, crystalline, and semicrystalline materials using schematic diagrams of material properties plotted as functions of temperature. Again, pressures affect the transition temperatures as schematically depicted in Fig. 1.27 for a semi-crystalline polymer. 

The thermal properties of the polymers reported in Table A.2 and Table A.3 were obtained by using a Perkin-Elmer Differential Scanning Calorimeter Model DSC-7 using a heating rate of 20°C/min. The specific heat was obtained using a heating rate of 10°C/min. For semicrystalline material, the heat of fusion was obtained from the measured specific heat curves. The crystallization temperature was obtained at 20°C/min cooling rate. 

G. P. Johari, in Plastic Deformation of Amorphous and Semicrystalline Materials, 1982 Les Houches Lectures, Les Editions de Physique, France, 1982, pp. 109-141. 

In (98) it was mentioned that a straightforward atomistic MD simulation of a semicrystalline material is not yet achievable, since crystallite dimensions may range from several 10 nm to several microns and crystallites often aggregate to form larger domains of macroscopic dimensions (35,36). In contrast, typical MD simulations use, for completely amorphous structures, cells with a length of a few nm. Therefore to simulate a semicrystalline cell several orders of magnitude larger seems to be completely out of question for nowadays computers. The possibility to adopt a less atomistic viewpoint and use a Monte-Carlo 2-phase simulation technique for semicrystalline polymers was analysed in (98). 

The main consequence of this reduced mobility is an extension of the glass transition region towards the high temperature side it will show a lower and an upper value, viz. Tg(L) and Tg(U), the values of the undisturbed amorphous region and that of regions with reduced mobility. By means of this model, Struik could interpret his measurements on volume relaxation (physical ageing) and creep in semicrystalline materials. 

Starch granules vary in size, shape, composition, and properties (Table I), and they are a semicrystalline material. Because the starch granule has a high degree of order, when viewed in polarized light it shows birefringence, the maltese cross of Fig. 1. 

The relaxation properties as probed by dynamic mechanical spectroscopy (DMS) for a series of ESI are shown in Figure 26.2. In accordance with the DSC results, the tan S loss maximum or Tg for the semicrystalline ESI appears to be fairly independent of styrene content. For the essentially amorphous ESI (>45wt% S), Tg increases with increasing styrene content. When compared with the amorphous ESI, the amplitude and width of the Tg loss peak are lower in amplitude and broader, respectively, for the lower styrene ESI, as is characteristic of a semicrystalline material. The amorphous ESI exhibit an intense loss process associated with the amorphous phase Tg(ESI). The width of this loss... 

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