3. a) A sample of polypropylene was synthesized with a new catalyst, then analyzed by H NMR. Based on the shifts present

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3 A A Sample Of Polypropylene Was Synthesized With A New Catalyst Then Analyzed By H Nmr Based On The Shifts Present 1 (128.45 KiB) Viewed 46 times

3. a) A sample of polypropylene was synthesized with a new catalyst, then analyzed by H NMR. Based on the shifts present in the spectrum, it was determined that the mechanism of chain transfer (ter- mination) was beta-methyl elimination. The aliphatic peaks were integrated versus the olefinic peaks and a ratio of 191 was calculated. What is the Mn of this polymer sample? b) A GPC is calibrated with monodisperse polystyrene samples, giving a log(MW) vs. VR plot that is perfectly linear, with the equation: log(MW) = -0.07*VR + 6.0. The polypropylene sample from part (a) was then run on the GPC (chromatograph shown below). Calculate Mw and Mn for the polymer. = 1 0.9 0.8 0.7 0.6 0.5 Detector Response (mass of polymer in arb, units) 0.4 - 0.3 0.2 0.1 0 0 5 10 15 20 25 30 35 40 45 50 55 60 VR c) Why do the Mns determined from NMR and GPC differ? For this example, which is the more accurate number? Why?