The molecular weight and molecular weight distribution (MWD) of linear polymers can be derived by using rheological methods. The mechanical excitation of polymers leads to a characteristic response of the material depending on its macromolecular structure. Using the HAAKE RheoWin software with optional tools like TTS (Time Temperature Superposition), Spectra and MWD (Molecular Weight Distribution) master curves, relaxation time spectra and molecular weight distributions can be easily generated out of dynamic tests (Oscillation frequency sweeps). Practical results are presented and discussed in this application report.
A well-established method to measure the molecular weight distribution is the gel permeation chromatography. This conventional method however has some disadvantages, which are e.g. solubility of the polymer, expensive instruments, time-consuming procedure and less sensitivity for high molecular components. Accordingly rheological methods are an interesting alternative. The theoretical relationships between the molecular weight distribution and material functions that can be determined through rheology are well investigated. Powerful numerical methods have been developed, which together with PC technology provide a means to determine
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