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Fraction, amorphous

Between T j, and Tg, depending on the regularity of the polymer and on the experimental conditions, this domain may be anything from almost 100% crystalline to 100% amorphous. The amorphous fraction, whatever its abundance, behaves like a supercooled liquid in this region. The presence of a certain degree of crystallinity mimics the effect of crosslinking with respect to the mechanical behavior of a sample. [Pg.202]

Pharmacological Action. Most of the early observations on the gelse-mium alkaloids were made on amorphous preparations, and the results reeorded are probably further confused by the faet that while in English journals the first erystalline alkaloid obtained was ealled gelsemine and the residual amorphous fraction gelseminine, these two names were used in the opposite sense in some German publieations. [Pg.740]

Both Cushny and Dale found the amorphous gelsemium alkaloids represented by such fractions as gelseminine much more active than gelsemine. Cushny stated that gelseminine resembled coniine in action and showed a greater depressant effect on the central nervous system, but unlike coniine it exerted no pressor effect. It was also a powerful mydriatic. Dale found that 0-001 gm. of the hydrochlorides of the amorphous alkaloids injected into rabbits caused death from respiratory failure in 25 minutes, preceded by convulsions. These results are explained by the subsequent isolation from such amorphous fractions, of the potent alkaloids sempervirine and gelsemicine. [Pg.740]

It was known for some time that even after the corticoids had been separated from crude extracts of the adrenal cortex, the remaining material, the so-called "amorphous fraction" still possessed considerable mineralocorticoid activity. Aldosterone (250), one of the last steroids to be isolated from this fraction, proved to be the active principle. This compound proved to be an extremely potent agent for the retention of salt, and thus water, in body fluids. An antagonist would be expected to act as a diuretic in those edematous states caused by excess sodium retention. Although aldosterone has been prepared by both total and partial synthesis, the complexity of the molecule discouraged attempts to prepare antagonists based directly on the parent compound. [Pg.206]

Fig. 15. 2H FT NMR spectra of the mobile amorphous fraction of LPE for various temperatures. The total magnetization was saturated first by a series of 90° pulses and then the solid echo was created after a waiting period r0 T, (amorphous) ranging from 25 to 200 ms... Fig. 15. 2H FT NMR spectra of the mobile amorphous fraction of LPE for various temperatures. The total magnetization was saturated first by a series of 90° pulses and then the solid echo was created after a waiting period r0 T, (amorphous) ranging from 25 to 200 ms...
Fig. 18.2H FT spectra of the alignment echo for different waiting times t2 and different temperatures. Sample LPE, amorphous fraction... Fig. 18.2H FT spectra of the alignment echo for different waiting times t2 and different temperatures. Sample LPE, amorphous fraction...
Layadi et al. have shown, using in. situ spectroscopic ellipsometry, that both surface and subsurface processes are involved in the formation of /xc-Si [502, 503]. In addition, it was shown that the crystallites nucleate in the highly porous layer below the film surface [502, 504], as a result of energy released by chemical reactions [505, 506] (chemical annealing). In this process four phases can be distinguished incubation, nucleation, growth, and steady state [507]. In the incubation phase, the void fraction increases gradually while the amorphous fraction decreases. Crystallites start to appear when the void fraction reaches a maximum... [Pg.151]

Other antibiotics still require freeze drying, e. g. Na-Cephalotin (Na-CET). Takeda [ 1.32] showed, that thermal treatment of Na-CET was not sufficient to produce pure crystalline Na-CET, as the amorphous fraction discolors during storage and must be avoided. Takeda described the production of pure crystalline Na-CET by adding microcrystals of Na-CET to a saturated solution of Na-CET. If this mixture was frozen and freeze dried, then no amorphous or quasi-crystalline were found. Koyama et al. [3.35] described, that after thermal treatment for 24 h some parts remained incompletely crystallized. After adding 5 % (w/w) isopropylalcohol, a thermal treatment of 1 h was sufficient. Furthermore, the product could be dried at a higher pressure. Thus the drying time could be reduced and 100 % of the product could be used. [Pg.218]

The investigators also presented a comparison of data on crystallinity drawn from the literature. This tabulation clearly shows the wide variations which have been reported. At first sight the values just presented, particularly for linters, may seem to be inconsistent with acid hydrolysis estimates. However, it was recognized that swelling could increase the amorphous fraction to 50 or even 100 times the amount occurring in dry unswollen material and that determinations based on aqueous solutions such as acids involve considerably swollen material. Hencp, values obtained by the latter methods may be reasonably correct as implicitly defined by test conditions. [Pg.137]

Crystallization of PET proceeds in two distinct steps [97], i.e. (1) a fast primary crystallization which can be described by the Avrami equation, and (2) a slow secondary crystallization which can be described by a rate being proportional to the crystallizable amorphous fraction dXc/dt = (Xmax — tc)kc, with Xmax being the maximum crystallinity (mass fraction) [98], Under SSP conditions, the primary crystallization lasts for a few minutes before it is replaced by secondary crystallization. The residence time of the polymer in the reactor is of the order of hours to days and therefore the second rate equation can be applied for modelling the SSP process. [Pg.75]

The papers of Mallon and Ray [98, 123] can be regarded as the state of the art in understanding and modelling solid-state polycondensation. They assumed that chain ends, catalysts and by-products exist solely in the amorphous phase of the polymer. Because of the very low mobility of functional groups in the crystalline phase, the chemical reactions are modelled as occurring only in the amorphous phase. Additionally, the diffusion of by-products is hindered by the presence of crystallites. The diffusivity of small molecules was assumed to be proportional to the amorphous fraction. Figure 2.32 shows the diffusion coefficients for the diffusion of EG and water in solid PET. [Pg.85]

O—CH2 bond) (78, 277). More precisely, the formation of the crystalline polymer in the presence of FeCla takes place according to such a mechanism, whereas the amorphous fraction of low or zero rotatory power produced at the same time contains a sizeable number of head-to-head, tail-to-tail sequences originating from reaction at the secondary caibon [O—CH(CH3) bond] with inversion of configuration (278). From a single enantiomer, for example, (5), one obtains, by attack at the primary caibon, a noninverted unit with (5) configuration and, by attack at the secondary carbon, an inverted unit with (R) configuration (279). [Pg.73]

With semi-crystalline polymers we should always carefully distinguish between the behaviour below Tg and above Tg. Below Tg (such as with PEEK) the crystalline fraction, which is somewhat stiffer than the amorphous glass, dominates, so that E is somewhat higher. Above Tg, such as with PE and PP, the amorphous fraction, which is in the rubbery condition, is responsible for a significantly lower E. [Pg.33]

In the first place the rate of diffusion of EDPE is higher, as a consequence of the higher amorphous fraction. Secondly, for the same reason, EDPE has a higher solubility (the solubility in the crystalline phase is very low). [Pg.41]

The infrared spectra of the obtained polymers have shown that they contain vinylidenic end groups (22). Quantitative data for the amorphous fraction of polypropylene are reported in Table IV (38). [Pg.39]

The high-molecular-weight poly (propylene oxide) produced with hexacyanometalate salt complexes shows no crystallinity. Moreover, it was shown by Price et al. (18) and confirmed in our laboratory that these polymers have more than 953 head-to-tail enchainment. The amorphous fractions of partially crystalline polymers made with metal-alkyl and ferrio-chloride-based catalysts were shown by those authors to have considerable head-to-head enchainment. They postulated that this was the cause of the amorphous nature of these fractions. It seems clear, however, that the amorphous nature of the polymers prepared with hexacyanometalate salt complexes must be the result of their low degrees of tacticity. [Pg.232]


See other pages where Fraction, amorphous is mentioned: [Pg.445]    [Pg.737]    [Pg.143]    [Pg.627]    [Pg.100]    [Pg.102]    [Pg.102]    [Pg.102]    [Pg.272]    [Pg.71]    [Pg.117]    [Pg.195]    [Pg.195]    [Pg.94]    [Pg.7]    [Pg.186]    [Pg.607]    [Pg.130]    [Pg.325]    [Pg.221]    [Pg.314]    [Pg.23]    [Pg.32]    [Pg.35]    [Pg.153]    [Pg.33]    [Pg.96]    [Pg.91]    [Pg.148]    [Pg.668]    [Pg.445]    [Pg.42]    [Pg.264]   
See also in sourсe #XX -- [ Pg.11 ]

See also in sourсe #XX -- [ Pg.45 ]

See also in sourсe #XX -- [ Pg.19 , Pg.41 , Pg.48 , Pg.49 , Pg.62 ]

See also in sourсe #XX -- [ Pg.170 , Pg.171 , Pg.193 ]




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