DMA investigation

Diminishing of the heights of the relaxation maxima of PU and PS constituents, their approaching and broadening, as well the increasing level of losses between maxima may testify to diminishing amounts of the two phases due to transition of some part of PU and PS into the interfacial region as a result of interaction with OUDM. 

An important characteristic of the two-phase systems is the degree of segregation asegr- Calculation of ctsegr has shown that an increasing amount of OUDM essentially diminishes this value from 0.31 for IPNs without com-patibihzer up to 0.10 for the IPN containing 10 mass %. This means that the introduction of the compatibihzing additive OUDM in the course of chemical reactions of IPN formation prevents microphase separation in the system, i.e., increases the compatibility. 

The most remarkable change in the relaxation properties occurs under introduction into the reaction system of 20 mass % of OUDM (Fig. 80d Table 19). hi this case instead of two maxima one observes only one broad maximum at 358 K, whereas the maximum corresponding to the PU phase degenerates and is revealed only as a shoulder (Fig. 80d). Such changes in the viscoelastic behavior may also be the result of morphological transformation [331]. For the formation of semi-lPNs in the presence of 20 mass % of OUDM, the compatibihty in the system increases. 

Introduction of 20 mass % of OUDM in all cases changes the relaxation properties (curves T-30, especially for PU/PS compositions 50 50 (curve 2 ) and 30 70 (curve 3 ). Instead of two maxima, these systems reveal only one maximum situated on the temperature scale between temperatures of relaxation transitions of separated phases in the initial IPNs. For these modified IPNs, microphase separation was not observed (Table 19). As is clearly seen from Fig. 81, the height of the maximum and its temperature position depend on the component ratio. 

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The DMA investigations have been also employed by us for PUs obtained with mixtures of diisocyanates. The materials were obtained in the Romanian laboratory. The two isocyanates were employed, MDI and DBDI, alone or as mixtures. The materials were synthesized with ethylene glycol (EG) as chain extender. The SS macrodiol was poly(ethylene adipate) PEA or polytetrahydrofuran (PTHF) of molar masses 2 000 g/mol. 

The similarity in morphology of four blends can be proved by the DMA investigation. In Fig. 24 elastic modulus and tan 8 of four blends are presented. The dynamic-mechanical behavior of the investigated blends does not differ from each other. It was found that CNTs mainly reside in the polar NBR and non-polar NR but not in weak polar SBR. Such unusual localization of CNTs in ternary SBR/NBR/NR can be explained by taking into consideration the presence of... 

The bromination of 4,5-j -dihydrocortisone acetate in buffered acetic acid does not proceed very cleanly (<70%) and, in an attempt to improve this step in the cortisone synthesis, Holysz ° investigated the use of dimethylformamide (DMF) as a solvent for bromination. Improved yields were obtained (although in retrospect the homogeneity and structural assignments of some products seem questionable.) It was also observed that the combination of certain metal halides, particularly lithium chloride and bromide in hot DMF was specially effective in dehydrobromination of 4-bromodihydrocortisone acetate. Other amide solvents such as dimethylacetamide (DMA) and A-formylpiperidine can be used in place of DMF. It became apparent later that this method of dehydrobromination is also prone to produce isomeric unsaturated ketones. When applied to 2,4-dibromo-3-ketones, a substantial amount of the A -isomer is formed. 

DMA. None of the three possible tetramethoxy analogs has been investigated, and the pentamethoxy analog does not produce DOM-like stimulus effects. From these studies, it is apparent that the 2,4- and 2,5-dimethoxy substitution pattern plays an important role certain 2.6-dimethoxy derivatives are also active, depending upon what substituents are present at the 4-position. 

For Rh and Ir diphosphine-based catalysts there exist some indications on reactive species and also on hydrogen activation. James and coworkers [43, 85] investigated the Rh-catalyzed DMA-imine hydrogenation and concluded that the imine is -coordinated to the Rh center via the nitrogen lone pair, and not via the 7i-system of the C = N bond. They also suggested that the hydrogen activation occurs after the imine is coordinated. 

The formation of dimers and trimers is a major issue in hydrogenations with iridium catalysts. In the context of developing an industrial process to produce (S)-metolachlor via an enantioselective imine hydrogenation (see Chapters 34 and 37), Blaser et al. investigated the causes of catalyst deactivation in the iri-dium/bisphosphine-catalyzed hydrogenation of DMA imine (Scheme 44.11) [84]. 

This interpretation is in agreement with the results of a recent Raman spectroscopic study 93) supporting the absence of [MX4 ]" — ions and also with the results of other spectrophotometric investigations 9X In the system AsI3-HMPA the final spectrum is obtained at a molar ratio D Asl3 = 2 1, whereas with the weaker donor DMA a considerable excess of donor is required in order to attain the final spectrum. 

Miura and Yoshida also investigated the changes in the microstructure of 1100 EW Nafion sulfonate membranes, in alkali, ammonium, and alkylammonium cation forms, that were induced by swelling in ethanol using DSC, dynamic mechanical analysis (DMA), SAXS, and electron probe microanalysis (EPMA). These studies were performed within the context of liquid pervaporation membranes that could potentially be used to separate ethanol from water... 

Another import field of development is the investigation of pesticides transformation products in food. Some examples are the investigation of the acaricide amitraz and its transformation products, 2,4-dimethylaniline (DMA), 2,4-dimethylformamidine (DMF), and N-2,4-dimethylphenyl-N-methylformamidine (DMPF) in pears [220] Antioxidant pesticides as well as their metabolites used in postharvest treatment have been investigated in pears and apples with concentrations in the ranges 0.002-0.672 ng/g (ethoxyquin), 0.94-11.86 ng/g (imazalil), 0.024-0.902 ng/g (diphenylamine), 0.012-2.59 ng/g (thiabendazole). 

A detailed investigation of aniline N-methylation on Cui xZnxFc204 was carried out through in situ FTIR spectroscopy. The reactants (aniline and methanol) and possible products (NMA, DMA and o-toluidine) were adsorbed on the catalysts and analyzed [106,107]. Adsorption of methanol indicated a dissociative chemisorption as methoxy species on catalyst surface at 100°C. As the temperature increased, oxidation of methoxy species to formaldehyde to dioxymethylene to formate species was observed, and above 300°C complete oxidation takes place to CO, CO2 and H2. Indeed methanol alone on Cui xZnxFc204 and Cui.xCoxFc204 behaves in a similar way [79,107]. 

For example, PINO (i.e. >N—O"), generated from HPI by oxidation with Pb(OAc)4 (cf. Scheme 7) or by laser flash photolysis of (t-BuO)2 (cf. Scheme 5) at 266 nm, has been investigated in the oxidative A-demethylation of 4-X-substimted-Af,Af-dimethylanilines (X-DMAs) (Scheme 11). ... 

The phase transition is directly related to the hydrophilic/hydrophobic balance in a copolymer and controlling the polymer composition provides a highly effective way of tuning the LCST. Another example of responsive polymer libraries was based on the combination of 2-hydroxypropyl acrylate and DMA or A-acryloyl morpholine [50]. The nitroxide mediated copolymerization conditions were chosen on the basis of the kinetic investigation of the homopolymerizations, as discussed in this chapter (see, e.g., Sect. 2.1.2). 

Similarly, the thermal transition behavior of the members of the P(DMA)- fflf-(HPA) copolymer library was investigated using DSC. For all members of this library, single Tg were obtained, which is an indication of a good mixing of the two... 

In the present study, sampling of both particulate and vapor forms of MMA, DMA, and p-APA was investigated and it was found that these compounds exist in air mostly in the particulate form. 

It is also interesting to look into the chemical interactions of organoclay (QUAT-modified MMT) with functionally polar rubbers like XNBR, CR, and their mutual blend. The role of layered silicate on the curing process of CR/XNBR blends was investigated through the study of curing kinetics, mechanical properties, WAXS, and DMA [74]. 

We present here our investigation of the influence of solute-solvent interactions on the quenching dynamics of perylene (Pe) and derivatives in an electron donating solvent, N,N-dimethylaniline (DMA) [4]. The electron acceptors and the donor solvent are shown in Fig. 1. 

First reported in 1986 (181), the complex [Os(NH3)5(acetone)]2+ and related aldehyde and ketone complexes (177) were the first examples of linkage isomerizations on Os(III/II). In acetone solution, a detailed electrochemical and chemical investigation revealed that the substi-tutionally inert complex, [Os(NH3)5(Tj2-acetone)]2+, is in facile equilibrium with the rj1 form, the former being favored by 21 kJ mol-1. Upon oxidation, the Os—C bond is ruptured, but the Os—O bond remains intact, even in good donor solvents such as dma. Reduction of the i71-acetone-Os(III) species occurs at a potential of 750 mV negative of that of the 172 form in acetone. Subsequent tj1 - 172 isomerization of the ketone occurs with a specific rate of 6 x 103 sec-1 at 20 2°C. 

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