Direct detection of end groups

529 spectroscopy have been used for polymer end group 

Garcia-Rubio et al. examined S and MMA polymerizations initiated by BPO and have shown that UV can be used to distinguish and quantitatively determine aliphatic and aromatic benzoate groups in MMA and S polymerizations. 

Buback et applied FTIR to follow the coui e of the initiation of S 

Buback et a A9 1 11,532 applied FTIR to follow the course of the initiation of S polymerization by AIBN and to determine initiator efficiency. Contributions to the IR signal due lo cyanoisopropyl end groups, AIBN, and the kelenimine can be separated using curve resolution techniques. 

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Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

Several research groups implemented carbohydrate analysis on-chip with direct detection of underivatized sugar molecules. Electrochemical detection is the most attractive approach, as it offers reasonable sensitivity and selectivity, and it is ideally suited for microchip format. Schwarz et al. [203] developed amperometric detection of sugars using microfabricated copper electrode. They separated fructose, sucrose, and galactose in 70 s on a glass chip with 50-p,m wide and 20-p,m deep microchannel and double tee injection geometry. The detection was based on Teflon-coated platinum wire plated with copper and inserted in the end of the separation channel etched in a conical shape. The detection limit down to 1 JtM was achieved. Hebert and coworkers [204] reported an... 

Liu and collaborators designed new electrochemical immunosensors based on chemical assembly of vertically aligned SWCNT on carbon substrates for direct detection of the pesticide endosulfan and the insecticide paraoxon " in spiked environmental water samples. In both electrochemical immunosensors, the applied SWCNT forest was fixed onto a GC electrode exploring the formation of amide bonds between the carbo)ylic functional groups at the SWCNT ends and the amine groups on the GC surface, which was previously modified with mixed layers of 4-aminophenyl and phenyl. This architecture was named as GC-Ph-NH2/SWCNT. 

On the basis of the polarographic studies, the direct electron transfer polymerizations of the monomers, of which half-wave potentials could be measured, were conducted keeping the potential at a level where the monomer alone was reduced and the electrolyte was not affected. During the electrolysis of a-methyl-styrene, for example, the red color of the carbanion was observed around the cathode, but dissipacted and vanished quickly. Only low polymers were found in the cathodic compartment, but no polymer in the anolyte. In the polymerization of other monomers almost identical results were obtained. From the fact that tri-n-butyl-amine was detected in the catholyte and analysis of the end group of polymers obtained, two possible termination steps were postulated ... 

Weak resonances corresponding to the expected para-substituted phenylsilyl end groups appeared, but the resonances corresponding to the potential vinyl end groups were not observed in the H NMR spectra of the poly(MMA)s within detectable limits. One may anticipate that the silane reactivity (which could be directly related to the hydrogen... 

Both end groups at the spacer molecule, OH and especially NH2, are important for further biochemical synthesis. As follows from XPS measurements, in all cases only 2% Br was not consumed and remained at the PP surface. It was assumed that either steric problems played a role or these bromine groups were not situated directly at the surface. For all glycolate spacers a functionalization density of about 5 spacer-bonded OH groups per 100 C was measured. Additionally, two directly at the surface bonded (without spacer) OH groups per 100 C atoms were also detected. 4-5 NH2 groups/100 C were found using... 

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