Orthorhombic crystallinity

Abstract. This paper presents results from quantum molecular dynamics Simula tions applied to catalytic reactions, focusing on ethylene polymerization by metallocene catalysts. The entire reaction path could be monitored, showing the full molecular dynamics of the reaction. Detailed information on, e.g., the importance of the so-called agostic interaction could be obtained. Also presented are results of static simulations of the Car-Parrinello type, applied to orthorhombic crystalline polyethylene. These simulations for the first time led to a first principles value for the ultimate Young s modulus of a synthetic polymer with demonstrated basis set convergence, taking into account the full three-dimensional structure of the crystal. 

Black phosphorus is the third major adotropic form of phosphorus. It occurs in two forms, one is an amorphous modification having a laminar structure similar to graphite and the other is an orthorhombic crystalline form. The density of black phosphorus may vary between 2.20 to 2.69 g/cm. Black phosphorus is obtained from white phosphorus by heating the latter at 220°C under an extremely high pressure of about 10,000 atm. 

Alpha cyclooctasulfur or the alpha-sulfur is yellow orthorhombic crystalline solid refractive index 1.957 density 2.07 g/cm at 20°C stable at ordinary temperatures converts to monoclinic beta form at 94.5°C. 

The degree of crystallinity may be calculated from the density of the polymer if the density is known for the amorphous and crystalline states. Some crystallizable polymers are polymorphic, i.e., they may exist in more than one crystalline form. An unstable crystalline form may change to a more stable form, and crystalline forms may change under stress. For example, hdpe changes from an orthorhombic crystalline polymer to a monoclinic form when subjected to compressive forces. 

The principal features of elemental sulfur in the displayed T, P range are the usual liquid and vapor phases and two solid forms, a-sulfur ( red sulfur, of orthorhombic crystalline form) and /3-sulfur ( yellow sulfur, monoclinic needle-like crystals), both of which are available as common stockroom species. The stable phase ranges for each elemental form are shown by the solid lines in Fig. 7.5. The liquid-vapor coexistence line terminates in a critical point at 1041°C, and will not be discussed further. 

The half-width of the crystalline component line was estimated to be 18 Hz. This value reflects the very stable orthorhombic crystalline phase of this sample. The component line shape centered at 31.0 ppm represents the contribution from the amorphous phase in which the molecular conformations are changed rapidly over all permitted conformations. The relatively narrow line width estimated as 38 Hz is caused by the rapid molecular motion. The line centered at 31.3 ppm represents the noncrystalline phase in which the local molecular motion can occur in the same manner as in the amorphous phase (in Tic time frame), but a long-range molecular motion accompanying a conformational change related to a 10-20 methylene sequence is severely restricted. The wide line width as 85 Hz... 

Spin-Lattice and Spin-Spin Relaxation. In order to examine the content of these crystalline and noncrystalline components, we examined the spin relaxation of each resonance line. Firstly it was found that the line due to the orthorhombic crystalline component at 33 ppm involves plural Tic s for all samples, as summarized in Table 4. In relation to the T1C for each sample, very long Tic values are recognized for three higher molecular weight samples. These values are expected... 

DD/MAS13C NMR Spectra. Figure 16 shows the equilibrium 13C NMR spectra of those samples that were obtained by the pulse sequence (7t/4-FIDdd-3Tic)ii at room temperature. Here the sample A is the undrawn dried gel, B is the sample obtained from A by annealing at 145 °C for 4 minutes, and C, D, and E are samples drawn 50,100, and 50 times, respectively For most spectra there is a recognized downfield resonance at ca. 33 ppm assignable to the orthorhombic crystalline component and an upfield resonance at ca. 31 ppm assignable to the noncrystalline component. 

Spin-Lattice and Spin-Spin Relaxations. In order to determine the content of these crystalline and noncrystalline resonances, the longitudinal and transverse relaxations were examined in detail. It was first confirmed that the noncrystalline resonance of all samples is associated with Tic in an order of 0.45-0.57 s. Hence, the noncrystalline component of all samples comprises a monophase, in as much as judged only by Tic. However, it was found that the noncrystalline component of drawn samples generally comprises two phases with different T2C values amorphous and crystalline-amorphous interphases. The dried gel sample does not include rubbery amorphous material it comprises the crystalline and rigid noncrystalline components. However, the rubbery amorphous phase with T2C of 5.5 ms appears by annealing at 145 °C for 4 minutes. For the orthorhombic crystalline component, three different Tic values, that suggest the distribution of crystallite size, were recognized for each sample, as normal for crystalline polymers [17,54, 55]. The Tic and T2C of all samples examined are summerized in Table 6. 

The longest Ti c of each sample increase with the increases in draw ration. However, even for 150 fold drawn sample (E) the Tic does not exceed 1650 s. This seems to reflect the phase structure of this type of sample. In addition to the orthorhombic crystalline resonance at 32.9 ppm, the existence of downfield resonance at 34.7-34.8 ppm assignable to the monoclinic crystalline component for all samples was confirmed by examining the relaxation phenomena. 

Fig. 19. Line shape analysis of the equilibrium spectrum of P420. The large dotted Lorentzians centered at 32.4 and 30.5 ppm and rather wide dotted Lorentzian centered at 32 ppm represent the orthorhombic crystalline and noncrystalline amorphous phases and crystalline-amorphous interphase, respectively. The dotted curve that is almost completely superimposed on the experimental spectrum indicates the composite curve of the component Lorentzians. dashed Weakly Lorentzians at 39, 34, 28, and 26 ppm represent the contributions from the methine and methylene carbons (a and p to the methine and methylene in the ethyl side group), respectively...

CH2) 1470 Lipids Splitting occurs for orthorhombic crystalline structures. In some cases, this band can be used to identify crystalline regions of fatty acids, such as palmitic acid. 

Fig. 18 Schematic two-dimensional presentation for crystallization of the interphase. With crystallization of the interphase in the open-orthorhombic phase, contraction in the orthorhombic crystalline lattice occurs. This results in the formation of dense orthorhombic or monodinic phase (see Figs. 15 and 16). In branched alkanes, because of the relatively sharp folds, the amount of chains contributing to the interphase is considerably less, which corresponds to the low intensity of the reflection assigned to the pseudo-hexagonal phase (see Figs. 12 and 14), while the phenomenon of concentration of the lattice with crystallization of the interphase is the same as in copolymers...

The solid-state structure for stannocene has not been determined the crystal structure for the orthorhombic crystalline form of plumbocene is shown in Fig. 2 (17), Plumbocene is associated in the solid state, with each lead atom coordinated to three cyclopentadienyl rings, one of them terminal and two of them bridging to other lead atoms. 

Figure 2.2 Orthorhombic crystalline structure of polyethylene perspective view of the unit cell and view along chain axis.

Spin-Lattice Relaxation. In order to determine whether each resonance line comprises a single component, we first measured the spin-lattice relaxation time Tic by the pulse sequence developed by Torchia [53] or by the standard saturation-recovery pulse sequence. The Tic values thus obtained were 2560,263 and 1.7 s for resonance line I and 0.37 s for line II. As reported by several investigators, the line at 33 ppm is associated with three different Tic values [ 17,54,55]. This means that this line is contributed to by three components with different molecular mobilities. However, since each component was represented by a single Lorentzian line shape at 33 ppm, they are all assignable to methylene groups in the orthorhombic crystalline form or in the trans-trans conformation. The component with a Tic of s can be assigned to methylene groups with a some-... 

Cooper SM. Orthorhombic crystalline form of fluticasone propionate and pharmaceutical composition thereof US patent 6,406,718, 2002. 

A C CP/MAS spectrum of C-labeled polyethylene in bulk at room temperature is shown in Fig. 9.14. As reported previously [4, 24-35], this spectrum consists of three peaks corresponding to an orthorhombic crystalline trans-zigzag methylene peak II at 33.0 ppm, a monoclinic crystalline trans-zigzag methylene peak I at 34.3 ppm and a noncrystalline methylene peak III at... 

Black Phosphorus. Polymorphic. Orthorhombic crystalline form stable in air resembles graphite in texture produced from the white modification under high pressures Bridgman, J. Am. Chem. Soc. 36, 1344 (1914) Jacobs, J. Chem. Phys. 5, 945 (1937) Krebe, Inorg. Syn. 7, 60 (1963), d 2.691. Does not catch fire spontaneously. Insol in organic solvents. Amorphous form prepd at lower pressures Ja-cobe, loc. cit At higher pressure the orthorhombic form undergoes reversible transition to a rhombohedral structure, d 3.56, and a cnbic structure, d 3.83 Jamieson, Science 139, 1291 (1963). 

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