Molecular weights, number average determination

Number-average molecular weights determined from GPC and H NMR. Estimated from H NMR. 

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

The number-average molecular weights determined from the gel permeation chromatograms showed an average deviation of 7% relative to the osmo-... 

The values obtained for are about one order of magnitude larger than the reported number-average molecular weights determined by the method of Manners et al. ( )... 

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... 

Calculate the number average, weight average from these data. Draw the molecular weight distribution curve and indicate in the plot the position of the weight- and number-average molecular weights. Determine the poly-dispersity of the sample. 

The number average molecular weight determines the colligative properties (i.e., those which depend only on the number of dissolved molecules) of polymer solutions. Measurements of freezing point depression (cryoscopy) or... 

M = number average molecular weight, determined by GPC M IM = molecular weight distribution (polydispersity). 

These values were used to calibrate GPC colunms for the polymer. Number-average molecular weights determined with modified calibration curves agreed well with those determined by embulliometry. The value of 0.96 for a was consistent with the idea that poly(3-alkylthiophene)s formed relatively stiff polymer chains in solutions. 

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

Figure 6.3 TOF-SIMS spectrum of PS standard in the range miz 3000-7200, showing the distribution of PS oligomers cationised with Ag. The number average molecular weight determined by TOF-SIMS, = 4550, is within 8% of...

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