Abstract
AbstractIn practical polymerization processes the goal is to control reaction conditions so as to produce polymers with optimum balances of properties for different applications. A key to success in this task is an understanding of the effects of the polymerization process on the molecular weight distribution (mwd) of the product as well as the response of polymer properties to changes in mwd. The effects of molecular weight and mwd on properties of commercial polymers made by free radical processes is dimly understood. Mechanical properties of polymer solids are theoretically related to mwd whereas the weight of the scanty evidence that is available suggests correlations with single average values, such as M̄n̄. By contrast, melt rheological properties are often referred to M̄w̄, while the evidence points to overriding effects of mwd.Analyses of mwd's by gel permeation chromatography have made great advances recently, but the value of the results is limited by the relative insensitivity of the technique in the high and low molecular weight regions of the distribution. The differences between various grades of the same commodity polymer are apparently due to nuances in mwd in these regions.Practical free radical polymerizations are very complex reactions. The reaction models must be correspondingly complex. Some illustrations of the value of experimental mwd data to guide predictions of kinetic schemes are given.
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