Deuterium exchange, polymer

The best insight into the relaxation behavior of star polymers in dilute solution can be expected if, in addition to the whole star system, different parts of the star are considered separately. This can be achieved easily by neutron scattering techniques on systems where not only the entity of arms, but also single arms, the core or shell parts are labelled by proton deuterium exchange. With respect to the core-shell labelling it is convenient to build up the arms as diblock copolymers of A-B type with protonated or deuterated but otherwise chemically identical A and B blocks. 

Several authors have reported that they did not succeed in isolating a number of pseudoazulenes when solutions in dilute mineral or glacial acetic acids were diluted with water or other bases.51-71,77-86 It was only possible to recover polymer-like material. In the subsequent decomposition the nucleophile attacks the conjugated acid of the pseudoazulenes at a position adjacent to the heteroatom, probably resulting in a fission. The hydrogen-deuterium exchange catalyzed by acids has been reported for systems 29,86 31,86 and 49.135... 

In this presentation, two examples of the use of vibrational spectroscopy to probe water-solid interactions in materials of interest to the food and pharmaceutical sciences are described. First, the interaction of water vapor with hydrophilic amorphous polymers has been investigated. Second, water accessibility in hydrated crystalline versus amorphous sugars has been probed using deuterium exchange. In both of these studies, Raman spectroscopy was used as the method of choice. Raman spectroscopy is especially useful of these types of studies as it is possible to control the environment of the sample more easily than with infrared spectroscopy. 

Check for Deuterium Exchange during Polymer Analysis. 

Infrared (IR) spectroscopy is perhaps the most convenient complementary technique for use with NMR. For example, we show in Fig. 3(a) (61) an IR spectrum of a soluble PHEMA. The polymer contains hydroxyls (3400 cm-1), saturated hydrocarbon functionality (circa 3900 cm-1 and 1500 1300 cm-1), and ester functionality at 1725 cm-1. Deuterium exchange brought about by exposure to d4 methanol vapor may be used to show that the in chain C-C skeletal vibration of PMMA at 1070 cm-1 which has been associated with atactic polymer, (79) has an analogue in PHEMA at 1080 cm-1 (Fig. 3b). Spectral subtraction after deuteration reveals also the primary alcohol C-O stretch of PHEMA at 1025 cm-1. 

A novel use ofthe salt [BMIM][PF6] is to enhance microwave absorption and hence accelerate the rate of a reaction. Ley found that [BMIM][PF6] enhanced the rate of the microwave promoted thionation of amides using a polymer supported thionating agent [304]. Hardacre et al. have developed a protocol for the synthesis of deuterated imidazoles and imidazolium salts [305]. The procedure involves the platinum- or palladium- catalyzed deuterium exchange of 1-methyl-d -imidazole with D2O to give 1-methylimidazole-d , followed by reaction with a deuterated alkyl halide. 

As seen in Chapter 11 (Hydrogen-Deuterium Exchange), infrared spectroscopy can be used conveniently for measuring the deuteration rate of biological polymers, e.g., polypeptides and proteins. Hydrogen isotopic exchange of DNA has been studied... 

Indirect methods of determining the degree of crystallinity start from the fact that a given chemical or physical event proceeds differently in the crystalline phase and in the amorphous phase. Common physical experiments include, for example, the study of water vapor absorption of hydrophilic polymers or the diffusion of a dye into the polymer. Together with a series of chemical reactions (hydrolysis, reaction with HCHO, deuterium exchange), they are used in particular for determining the crystallinity of cellulose. 

An alternative technique for the separation of the crystalline and amorphous contributions to the absorption bands of functional groups containing labile hydrogen atoms (e.g. —OH, —NH) is deuterium exchange (see below). The principal advantage of this experimental method is that it offers the possibility of studying independently the preferential alignment of chemically identical structural units in different phases of the polymer. 

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