a high MW dispersity are more suitable for extrusion. Polymers with a MW dispersity of 1.0 can be produced only by biological systems. Many physical properties can be affected by the MW dispersity.
The physical and chemical properties of the polymers in general are directly related to the MW, MWD, MW dispersity, and long-chain branching [18, 19]. Table 17.2 shows the relationship between the average MWs and some physical properties of polymers. There is also a relationship between the MW and the viscoelastic properties of polymers [20, 21] and thus it is possible to predict some properties of the polymer with a simple determination of the MW by GPC. Polymers with high MWs have higher viscosity, they also present low melt flow index, and are more difficult to dissolve, since they present higher chemical resistance; polymers with very high MW are more difficult to process and require higher temperatures.