Endgroups, determination

Pacsu4 5 has suggested a structure for starch involving a small number of non-cyclic hemiacetal linkages, the number being presumably sufficient to account for the number of endgroups determined by the methylation method. Halsall, Hirst and Jones6 have commented on this structure, however, and have shown it to be incompatible with the results of periodate-oxidation studies. In addition, these authors pointed out that it would be difficult to explain enzymic hydrolysis and dextrin formation on the basis of such a structure. 

Moreover polyPc may exist in a two-dimensional parquet-floor (86) or a one-dimensional ribbon structure 93). No method is known to decide exactly between both structures. Mainly (86) and 93) in different ratios will be present in a polyPc. Only the combination of an absolute method of molecular weight and endgroup determination may solve this problem. 

Koster, S., Duursma, M. C., Boon, J. J., and Heeren, R. M. A. Endgroup determination of synthetic polymers by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. /. Am. Soc. Mass Spectrom., 11,536, 2000. 

The — CH2— COO and —COO—CH2 methylene protons present resonances in the 2.1-2.4- and 4.0-4.3-ppm ranges, respectively. The peaks of -CH2OH endgroup methylenes appear close to 3.8 ppm in most aliphatic polyesters and can be used for the determination of the OH endgroup content. In the spec-tra of PET recorded in CD2CI2/CF3CO2D, these peaks (a triplet) are shifted to... 

The molecular weights of PAs are often not very high (M > 20,000) in this range M can be determined by endgroup analysis or, less frequently, by osmometry, Mw can be determined by light scattering. Both M and Mw can indirectly be determined by HPLC. 

Other endgroups can indirectly be quantified by first hydrolyzing the polymer in diluted chloric acid solution and then determining the composition of the compound by HPFC, reverse-phase chromatography, or gas chromatography (GC).45 48... 

Mandal and Hay28 used MALDI-TOF mass spectrometry to determine the absolute molecular masses and endgroups of 4-phenylphenol novolac resins prepared in xylene or chlorobenzene. Peaks with a mass difference of 44 (the molecular weight of a xylene endgroup) suggested that reactions conducted in xylene included some incorporation of xylene onto the chain ends when a strong acid such as sulfuric acid was used to catalyze the reaction. By contrast, no xylene was reacted into the chain when a milder acid catalyst such as oxalic acid was used. No chlorobenzene was incorporated regardless of the catalyst used. 

Endgroup analyses were carried out with an automatic potentiometer. The [-NH2] and [-C00H] were determined simultaneously. The polymer was dissolved in o-cresol/chloroform mixture (70/30), excess alcoholic KOH added and titrated with alcoholic HCl (0.1 N). The inherent viscosities were determined in0.5% solutions... 

The results of the reaction of finely devided powdered polymer (0.1reaction times and temperatures are given in table 1. On some samples both and (/P) have been determined but as the aci and amine endgroup concentrations do not differ much,(M ) = (/P). The... 

Thus, the reaction rate seems not to be determined by the of the reaction, nor by the diffusion of the condensate. This, and the susceptibility of reaction rates to variations in starting molecular weights make us believe that the process limiting step is the diffusion of the reactive endgroups. 

Many methods have been proposed for determining the efficiency,/ of the initiator. The most direct method depends on a quantitative assay of the polymer for initiator fragments, and its comparison with the amount of initiator decomposed. This is not difficult in those cases where the initiator leaves a reactive endgroup on the polymer or is radioactively tagged. 

Except the method of endgroup analysis all the above methods are based on the determination of properties of polymer solution. The Molecular weight of the polymer is related to its chain length or to the degree of polymerisation (DP) defined as the ratio between the Molecular weight of polymer and that of the monomer. 

Thus the Endgroup analysis method is quite useful for the determination of the Molecular weight of the polymers that possesses endgroups which can be determined precisely by some analytical reaction. In addition to Polyamides and polyesters, where the Endgroup analysis method is commonly used, the method can also be used for polysaccharides. 

Dye techniques are very sensitive and are characterised by simplicity and rapidity of operation. For these only common equipment are needed. Sometimes, the Dye technique is the only suitable method for the determination of OH endgroup. 

In addition, the determination of a polymer s endgroup(s) [125,126] and the analysis of random and block-copolymers [127,128] can be achieved by MALDI. However, care has to be taken when judging the MALDI spectra because of the mass-dependent desorption and detection characteristics of the experiment. In case of higher polydispersity (PD >1.1) high-mass ions are underestimated from MALDI spectra. [93,124] The current practice to deal with such samples is to fractionate them by gel permeation chromatography (GPC) [123] or size-exclusion chromatography (SEC) prior to MALDI analysis. [124,129]... 

One possibility is hydroxyl endgroups, which may be formed by a side reaction of sulfate ion-radicals to form hydroxyl radicals (9) or hydrolysis of the surface sulfate groups. To determine if hydroxyl groups were present, the ion-exchanged latexes were oxidized by heating with persulfate and 10 silver ion at 90°, then ion exchanged and titrated conductometrically to determine the carboxyl groups. Table II (9) shows that some sul-... 

To determine the effect of different polymerization conditions on the polymer endgroups produced, polymerizations were carried out using the standard bicarbonate buffer as well as other variations. Table V (13,16) shows that the use of the persulfate-bicarbonate combination with and without emulsifier gave latexes of final pH 7-8 with only sulfate groups. The addition of 10 5 silver ion gave a latex of pH 8.5, but with weak-acid groups, presumably because of oxidation of the sulfate groups. 

To procure a full-scale hydrodynamic model, we may need microrheological data [85-89] (especially for PFPEs with polar endgroups, i.e., Zdol). When the microrheological data are not available, one could use a simplified form of q(z) = pg/( -j to develop the improved hydrodynamic model. Here p/ is the bulk viscosity and / is a function of z to be determined experimentally. A partial justification for the abovementioned functional form can be drawn from the temperature dependence of the surface diffusion coefficient and the bulk viscosity [10], or the fly stiction correlation with the bulk viscosity [9]. We examine the rheological properties of PFPE separately in Section II.C. 

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