Deuterated phase separation

Reactions at Eqs. (12) and (13) are carried out in toluene solution. The yellow crystalline products are purified by recrystallization from pentane and stored in a dry atmosphere at —20 °C. Reaction at Eq. (14) takes place slowly at 20 °C in benzene. The sulfane product H2S is separated from the silylester side product by distillation together with the benzene solvent (in the case of n=2-4) or by phase separation (for n=4, 5). For certain preparative purposes the ester and the solvent may not interfere. If deuterated triflu-oroacetic acid is used in the reaction at Eq. (14) the fully deuterated sulfane is obtained [29]. 

Soil Addition of 10 ml water and deuterated standards to 50 g of soil followed by equilibration for 1 h. Sonication 3 times with acetone/ hexane. Phase separation followed by water removal using sodium sulfate, concentration using K-D, and nitrogen blow-down. Spiking with phenanthrene-... 

The bilayer morphology of thin asymmetric films of may be unstable. A regularly corrugated surface structure of the films was ascribed to spinodal transition into a laterally phase separated structure, where the surface morphology depended on the polymer incompatibility and the interfacial interactions [347, 348]. Recently, the phase separation and dewetting of thin films of a weakly incompatible blend of deuterated PS and poly(p-methylstyrene) have been monitored by SFM [349, 350]. Starting from a bilayer structure, after 454 h at T= 154 °C the film came to the final dewetting state where mesoscopic drops of... 

In this case study, which is extracted from reference 184, infrared dichroism is described as a means of separating the component dynamics in multicomponent polymer melts. What is necessary is the existence of distinct absorption peaks for at least one of the components. In the present problem, however, where two chains of identical chemistry but different molecular weights are mixed, there will not be any intrinsic differences in their absorption spectra. In this case it is necessary to label one of chains with a tag that will allow its presence in the blend to be revealed. For this purpose, deuteration of one of the chains is often used. This provides the labeled chain with an absorption of infrared light at the symmetric stretching vibration of the C-D bond, which occurs in the vicinity of 2180 cm-1. Fortunately, the unlabeled polymer contains no absorption peak at this location. It is important, however, to determine that the presence of a label on one species will not alter the physical response of the sample at a level that will affect the phenomena under study. For example, the labeling should not induce phase separation or cause unwanted specific interactions. 

Another strategy for stable isotope labeling of N-terminus and lysine side-chain amines is reductive animation by nondeuterated and deuterated formaldehyde. Dimethylation of peptides occurs by the formation of a Schiff base, followed by reduction with cyanoborohydride. Peptides thus labeled differ by a mass of 4 Da for each labeled pair. The labeled peak pairs show minimum isotope effects on reverse-phase separation and hence coelute (93). Dimethylation using formaldehyde with the natural isotopic abundance (hydrogen and 12C) versus a heavy form with two deuteriums and one atom of 13C... 

The temperature-independent term A is referred to as the entropic part of. while BjT is called the enthalpic part . The parameters A and B have been tabulated for many polymer blends and we list representative examples in Table 4.3. Isotopic blends typically have small positive x parameters (deuterated polystyrene blended with ordinary polystyrene f/PS/PS is an example) making them only phase separate at very high molar masses. PS/PMMA has four entries in Table 4.3, which reflect the differences encountered by labelling various species with deuterium. PS/... 

We can exploit mixtures of per-deuterated and per-hydrogenated polymers in small-angle neutron scattering measurements to reveal information on the configuration of individual chains as well as assemblies of chains in the case of phase separating blends, block copolymers, and other inhomo-... 

Zumbulyadis et al. [133-135] showed that proton to deuterium CP transfer is also useful to investigate miscibility. For a completely deuterated PMMA (d8-PMMA) homopolymer, a very weak deuterium FID signal, which was created by CP between a small amount of residual protons ( 2%), was detected (Fig. 10.17(a)) [134], For miscible d8-PMMA/PVPh = 18.8/81.2, an appreciable enhancement was observed (Fig. 10.17(c)). However, for the phase-separated blend, the signal enhancement was small as compared to that for the miscible one (Fig. 10.17(b)). They concluded that the signal enhancement in the phase-separated blend comes from interfacial regions (see Section 10.3). 

Fig. 10.17. Time-domain CP/MAS NMR spectra of pure deuterated-PMMA and deuterat-ed-PMMA/PVPh = 18.8/81.2 (a) Only a very weak signal due to CP from residual H is observed for deuterated-PMMA (b) time-domain signal of a partially phase-separated blend cast from tetrahydrofuran and (c) time-domain signal of a homogeneous blend cast from methylethylketone. (Reprinted with permission from Ref. [134]. 1993 American Chemical Society, Washington, DC.)...

It should be noted that deuteration may change conformation of macromolecules and their solubility [Utracki, 1989]. Theory predicts phase separation (with UCST) for a blend of hydrogenated with deuterated polymer [Buckingham and Hentschel, 1980 Edwards, 1983 Honeycutt,... 

Microscopically Viewed Structural Characteristics of Polyethylene Blends Between Deuterated and Hydrogenated Species Cocrystallization and Phase Separation... 

Fig. 23. Use of neutron contrast variation to examine lateral phase separations in liposomes composed of a 3 7 mixture of deuterated DMPC (Table 6) and protonated DMPA (dimyristoyl phosphatidic acid) at 30°C. The chain melting transition is 23 C. Thickness Guinier plots of were...

A major application of solid state NMR is the study of polymer morphology. Information potentially available includes the amount and orientation of crystalline phases in semi-crystalline polymers and the domain sizes in phase-separated polymeric systems. For the determination of crystallinity, a common method is to measure Ti relaxation in NMR (or NMR for deuterated polymers). The relaxation data can often be resolved into two (or more) components, which may correspond to magnetization arising from crystalline and amorphous phases (11-15,130-134). The development of the maximum entropy regularization method has permitted more facile and less subjective analysis of the data (143). In optimal cases, multiple components can be identified. 

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