Molecular weight determination by end-group analysis

The molecular weights of fatty polyamides generally encompass the range of 3000-15,000. Anderson and Wheeler (10) evolved a relationship for number-average molecular weight determined by end-group analysis and viscosity so that molecular weight can be... 

The major molecular weight determination methods include number average molecular weights determined by end-group analysis. 

Hydroxyl number and molecular weight are normally determined by end-group analysis, by titration with acetic, phthaUc, or pyromellitic anhydride (264). Eor lower molecular weights (higher hydroxyl numbers), E- and C-nmr methods have been developed (265). Molecular weight deterrninations based on coUigative properties, eg, vapor-phase osmometry, or on molecular size, eg, size exclusion chromatography, are less useful because they do not measure the hydroxyl content. 

EXAMPLE 4.5 Empirical Determination of the Mark-Houwink Coefficients for a Polymer Solution. The molecular weights of various polycaprolactam preparations were determined by end-group analysis (see Example 3.2) intrinsic viscosities of the various fractions in m-cresol were measured at 25°C. The following values are representative of the results obtained (Reim-schussel and Dege 1971) ... 

Comparison of GPC and End-Group Molecular-Weight Values. Molecular-weight values determined by end-group analysis and by GPC are compared in Table V. 

Molecular weights are determined by end-group analysis (Mn), membrane osmometry (Mn), viscometry (Mv), size exclusion chromatography (Mm), light scattering photometry, and sedimentation (Mw). Any molar mass computed by these methods must be evaluated critically, in view of a dependence on methodology. 

NMR Detailed structural information molecular weights can be determined by end group analysis solid-state cp-mas techniques can be used to characterize solid samples and cross-linked elastomers 673-681... 

The molecular weights of the polymers were determined by end-group analysis for hydroxyl. Since the polymers are linear and terminate at each end with a hydroxyl group, the number-average molecular weight is calculated from Eq. (15) ... 

The average degree of polymerization (n) determined by end group analysis from NMR spectra, except for the low molecular weight products, where a combination of GC and NMR was used. 

The molecular weight and molecular weight distribution may be determined by conventional techniques. As the resins are of comparatively low molecular weight it is possible to measure this by ebullioscopic and by end-group analysis techniques. 

The second method is a variation of the first in which the number of initiator fragments in the polymer is determined by direct analysis of the polymer end groups. The analysis is relatively difficult to perform accurately because of the low concentration of the end groups. For a 50,000-molecular-weight polymer, the end groups constitute only 0.1% of the total... 

When a material is present in pure form, it is possible to obtain tentative information about its molecular weight by employing various chemical analytical procedures, primarily (a) elemental analysis, (b) determination of combiniUj weights, and (c) end-group analysis. 

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