Gel permeation chromatography of polyethylene. II. Rapid evaluation of long-chain branching and molecular weight distribution

Abstract

A comparison is made of two methods by which one may derive molecular weight distribution and degree of long-chain branching using only the measured solution viscosity of a branched polyethylene whole polymer and its GPC trace. These are (a) Drott and Mendelson method and (b) Ram and Miltz procedure. In each case, the purpose of the method is to devise a means by which one may establish a relationship between solution viscosity and molecular weight for use in conjunction with the GPC universal calibration relationship of Benoit et al. The effectiveness of these theoretical approaches is evaluated by comparison with the true D and degree of long-chain branching data obtained using our complete iterative analysis method. Such a detailed comparison using low, moderate, and highly branched resins leads to a conclusion that both the techniques provide very good MWD and branching data and, further, that they may be considered interchangeable for most resins. For highly branched resins, the Ram and Miltz method, which is slightly more sensitive to the presence of a high degree of long-chain branching, is preferred. In practice, the Drott and Mendelson method has the advantage of using less computer time and providing a direct measure of degree of long-chain branching, and thus is likely to be used most frequently.