Strength of Polymers Is Related to Molecular Weight, with Higher Values Usually Conferring

PolyethyleneCompounderPolydispersity

Strength of polymers is related to molecular weight, with higher values usually conferring more strength and toughness (this is largely why milk cartons are stronger than candles—chemically, they are almost the same formula). A polyethylene vendor receives a call from a processor who wants to test a new formulation that he hopes will allow him to process at lower temperatures, thereby saving energy and money. He wants a mixed resin containing high and low molecular weight components. After talking to the vendor about the different grades available, the customer decides to try a 50% weight mixture of Grade A and Grade X. Grade A is nearly monodisperse, with a molecular weight of 25,000 by GPC (be patient--we WILL tell you how GPC measures molecular weight). Grade X is nearly monodisperse, with a molecular weight of 75,000. The total sample required is 200 lbs, so the vendor blends 100 pounds of each grade to produce the desired blend. It’s a huge success, and the processor decides to purchase 50 tons per month. For certification in Japan, the processor must specify the various molecular weight averages used to make his product. Compute Mn, Mw, Mz and Mz+1 for this blend.