Hexafluoroisopropanol solution

Thienyl(phenyl)iodonium salts and other heteroaryl(phenyl)iodonium salts can be used as the selective heteroaryl transfer agents in reactions with phenol ethers. These heteroarylations occur at room temperature in the hexafluoroisopropanol solution in the presence of trimethylsilyl triflate via a SET mechanism [876]. 

The derivatisation of the polyester is carried out in a 10% mmol solution of dichloroacetic anhydride in dichloroacetic acid at 60 °C. A reaction time of 1 hour suffices. After the reaction, the solution is poured into water and the precipitated polymer washed out. To remove the last traces of solvent and acetylation agent, reprecipitation of the derivatised polymer from a hexafluoroisopropanol solution into water is carried out. For polymers with low hydroxyl content (<100 mmol/kg), reprecipitation is carried out from a solution in nitrobenzene into cold light petroleum to obtain more reproducible results. 

All polyimide alloys were solution blended at a 50/50 weight ratio by codissolving the polymer pairs in a common solvent, such as methylene chloride (MeCl2) or a mixture of MeCl2 and hexafluoroisopropanol (HFIP), co-precipi-tating in methanol and then drying overnight under vacuum at 100 °C. 

In concentrated sulfuric acid, aromatic polyisocyanides are subject to sulfona-tion. Poly(isopropyl isocyanide) is dissolved in 97%H2S04, and is reprecipitated by the addition of water. Infrared spectra show that some structural change, e.g. hydrolysis, has taken place (26). Poly(sec-butyl isocyanide) is dissolved by the acidic hexafluoroisopropanol with some attendant browning of the solution (7). In spite of the theoretical complexities of polyelectrolytic character introduced into the solution characterization of polyisocyanides in strongly acidic media, such media at least allow viscometric indexing of the various samples of the otherwise insoluble polyisocyanides. 

Blends of these starting materials were obtained by coprecipitation from solution in hexafluoroisopropanol. Amorphous films were then obtained from the precipited powder by melt pressing in vacuo for different times varying from 0.2 min to 45 min followed by quenching in ice-water. In this way PET/PEN blends with weight compositions 90/10,70/30,60/40,44/56,30/70 and 10/90 were prepared. 

Eby RK et al. Production of nonwoven network of synthetically spun silk nanofibers, by electrospinning a solution containing dissolved silk fibers and hexafluoroisopropanol. University of Akron, OH... 

Polymer VII from 1,4-Cyclohexanedione and 1,2,4,5-Tetrakis-(hydroxymethvl) cyclohexane. Into a 100—ml flask equipped with a mag. stirrer, a Dean-Stark trap, a reflux condenser and a drying tube were added 50 ml of dry n-butyl ether, 2.04 g of 1,2,4,5-tetrakis(hydroxymethyl)cyclohexane and 1.12 g of 1,4-cyclohexanedione. The solution-suspension was heated under reflux for 12 hours followed by the addition of 0.1 g of -toluenesulfonic acid. After the mixture was heated overnight, it was cooled to room temperature. The mixture was filtered with suction and the resulting solid was washed well with n-butyl ether. After most of the ether was removed, the solid was washed with water, acetone and finally ether. The solid, which was dried over P2O5 and under 0.2 mm pressure, weighted 3.1 g (99%). The solid was soluble only in hexafluoroisopropanol and had an [T ] of 0.04 dl/g at 25°c. The polymer was found to be crystalline by X-ray and did not melt. 

In contrast, such peaks could be significantly displaced to high frequency when an alternative type of a-helix (airhelix) is present in which the amide plane might be tilted from the helical axis as previously proposed by Krimm and Dwivedi95 as the major form of transmembrane a-helix present in bR on the basis of an anomalously high frequency of the amide I band. The characteristic peak position of the l3C chemical shifts of the airhelix can be defined, taken similarly to the infrared spectra by using (Ala) dissolved in hexafluoroisopropanol (HFIP) solution,96 as demonstrated in Table 2, together with the l3C chemical shifts of... 

Solid-state NMR confirmed that peptide PrP109-122 can exist in at least two different conformations, depending on the solvent from which the final preparation is obtained (Heller et al, 1996). Although peptide lyophilized from acetonitrile/water solution showed p-sheet structure in the segment spanning residues 112-121, the sample lyophilized from hexafluoroisopropanol had a metastable a-helical conformation in the segment comprising residues 113-117. The expo-... 

Figure 6. NMR spectra of Hytrel 4056 (a-c) and Hytrel 7246 (d-f) obtained at 50.3 MHz. Key a and d, solid state spectra obtained with magic-angle spinning at ca. 2.2 kHz, cross-polarization (0.5 ms contact time), and dipolar decoupling at ambient temperature b and e, spectra a and d with sidebands removed ( see text for line assignments), c, solution state spectrum in m-cresol at 100°C f, solution-state spectrum in hexafluoroisopropanol at 34 °C. The spectra in c and f were broadened artificially and the solvent lines were removed.

Figure 18 Uptake ( /oS) of Lewis acids by PMMA and ArMCU versus the acidic character of the solutes. The %S is the solute per repeat unit molar ratio in the case of PMMA and the solute per nitrogen atom in the case of ArMCU. The solutes were characterized by AN, the Gutmann acceptor number CCI4, 2.3 l-2,dichloroethane (DCE), 6.4 dichloromethane (DCM) (CH2CI2), 13.5 trichloromethane (TCM), (chloroform) 18.7 hexafluoroisopropanol (HFIP), 66.3 and tri-fluoroacetic acid (TFAA), 111.

NMR can be assigned to the peak position of the an- helix (16.7-15.5 ppm) and its boundary with the ordinary aj -helix (15.5-15.0 ppm), with reference respectively to the chemical shifts of (Ala)n in hexafluoroisopropanol (HFIP) solution or solid... 

There were also attempts to calibrate the SEC columns with help of broad molar mass dispersity poplymers but this is less lehable. The most common and well credible SEC cahbration standards are linear polystyrenes, PS, which are prepared by the anionic polymerizatioa As indicated in section 11.7, according to lUPAC, the molar mass values determined by means of SEC based on PS calibration standards are to be designated polystyrene equivalent molar masses . Other common SEC calibrants are poly(methyl methaciylate)s, which are important for eluents that do not dissolve polystyrenes, such as hexafluoroisopropanol, further poly(ethylene oxide)s, poly(vinyl acetate)s, polyolefins, dextrans, pullulans, some proteins and few others. The situation is much more complicated with complex polymers such as copolymers. For example, block copolymers often contain their parent homopolymers (see sections 11.8.3, 11.8.6 and 11.9). The latter are hardly detectable by SEC, which is often apphed for copolymer characterization by the suppliers (compare Figure 16). Therefore, it is hardly appropriate to consider them standards. Molecules of statistical copolymers of the same both molar mass and overall chemical composition may well differ in their blockiness and therefore their coils may assume distinct size in solution. In the case of complex polymers and complex polymer systems, the researchers often seek support in other characterization methods such as nuclear magnetic resonance, matrix assisted desorption ionization mass spectrometry and like. 

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